EXHAUST GAS EMISSIONS OF SMALL CAPACITY TWO STROKE AND FOUR STROKE ENGINES

Transcription

1 INSTITUTE FOR INTERNAL COMBUSTION ENGINES AND THERMODYNAMICS GRAZ UNIVERSITY OF TECHNOLOGY EXHAUST GAS EMISSIONS OF SMALL CAPACITY TWO STROKE AND FOUR STROKE ENGINES Dr. Mario Hirz Dr. Roland Kirchberger Dipl.-Ing. Matjaz Korman PRESENTED AT THE TRAINING TVS OF TÜV RHEINLAND GROUP IN KÖLN DECEMBER

2 1. OVERVIEW OF TWO STROKE AND FOUR STROKE ENGINE TECHNOLOGIES IN SMALL CAPACITY APPLICATIONS Small capacity spark ignition internal combustion engines come to use in wide spread product applications. The big number of functional ranges requires different demands on the power units, leading to various realized engine designs. The world beside passenger car and heavy truck engines presents itself as a cheerful market with extraordinary solutions for specific requirements. The cylinder capacities of these engines are spreading between 20cc in small hand held tools and 800cc in offroad motorcycles, the power output varies between 0.5kW in small portable utilities and about 140kW in snowmobile engines. Depending on the operational demands, naturally aspirated or supercharged, two stroke or four stroke, heavy or light weight concepts come to use. In Table 1.1 an overview of small capacity engine application classes is listed; in addition the development trends are described by short remarks. Application: Motorcycles Scooters Marine Agricultural and garden equipment Hand held tools Snow mobiles Snow removal equipment Remarks: With exception of the 50cc class the trend definitely goes to four stroke technologies with fuel injection (FI) systems in combination with exhaust gas after treatment strategies. Same prediction as above, whereas the average displacement value in scooter applications is smaller than in motorcycle appliances. Two stroke engines in the lower end of the power output range, otherwise an introduction of four stroke engine technologies in most of the new products. Four stroke engine technologies are widespread, two stroke engines come to use in specified fields. Domain of two stroke engines because of the 360 position usage in combination with a high power density. Introduction of four stroke technologies in the last years. Because of the extreme demands on maximum power output and engine weight a bastion of two stroke technologies, but some manufac-turer also offer four stroke engines for a short time. Both, two stroke engine and four stroke engine applications with a trend to the four stroke direction. Recreational vehicles Four stroke technologies entered this typical two stroke application fields in the last years too. Portable power generators Most of the sold generators are driven by small four stroke engines. Table 1.1: Applications of small capacity internal combustion engines More severe exhaust emission regulations and a higher customer sensibility regarding the environmental friendliness of internal combustion engines lead to an implementation of four stroke technologies into most of the applications, whereas - 2 -

3 both, two stroke and four stroke concepts, are often combined with exhaust gas after treatment systems, like secondary air induction or / and catalytic conversion TODAY`S AND FUTURE TECHNOLOGIES OF SPARK IGNITION INTERNAL COMBUSTION ENGINES IN SMALL CAPACITY ENGINE TWO WHEELER APPLICATIONS The increase of the individual traffic in the last decades, especially in congested areas, and the predicted rates of growth will put forth more severe exhaust emission regulations for two wheeler vehicles driven by small capacity engines, which will lead to the implementation of advanced engine control units, comparable to systems used in automotive applications, into low cost vehicles. Whereas in cars and premium class motorcycles complex engine management systems and exhaust gas after treatment procedures are standard, the engines of low cost vehicle classes mainly use simple systems. Nowadays, most of the disposed 50cc two wheeler vehicles in Europe are driven by two stroke engines with carburetor technology in combination with an oxidation catalyst. Four stroke engines are niche products in Europe, but widespread in some Asian markets. In the autumn of 2003 a Japanese manufacturer entered the market with a scooter driven by a 50cc four stroke engine with an electronic fuel injection system. European manufacturer introduced air assisted direct injection systems for two stroke engines in the course of the last years. Figure 1.1 illustrates a selection of exhaust gas emission legislations and future prospects in target markets. The displayed limiting values are not directly comparable, because the measurement procedures as well as the test cycles differ in several markets. In this way, the proposal serves as an overview of expected scenarios. Fig. 1.1: Emission legislations in selected markets. Source: Orbital Engine Company [1] - 3 -

4 In the field of small internal combustion engines for the application in two wheeler vehicles the cost pressure is very high. In contrast to high performance motorcycles, where the customers ask for the latest technologies, the drive units of small displacement scooter classes (125cc or less) must be both, robust and easy to handle, and that in combination with low production costs. In comparison with conventional two stroke engines the four stroke working principle produces less hydrocarbon and particulate exhaust emissions, mainly based on significantly minor scavenge losses. To exemplify the differences of the emission characteristics, Figure 1.2 shows a comparison of hydrocarbon and nitrogen oxide exhaust emissions detected in an European driving cycle for mopeds with 50cc displacement. The Euro II emission targets can be reached with a low cost four stroke technology (carburetor) without exhaust gas after treatment. In order to fulfill the exhaust legislation two stroke engines in the treated class have to be equipped with an exhaust gas after treatment and / or an upgraded gasoline direct injection system. A detailed study of different two stroke and four stroke technologies regarding their qualification for future exhaust gas emission regulations is treated in Chapter 2 and 3. 3,5 [g/km] 3 2,5 2 1,5 1 0,5 0 Watercooled 4Stroke, Carburetor Fan cooled 4Stroke, Carburetor Watercooled 2Stroke, DGI Air cooled 2Stroke, Carburetor Euro II Limit HC NOx HC+NOx Fig. 1.2: Typical untreated HC and NOx exhaust emissions of 50cc mopeds in the European ECE R47 driving cycle - 4 -

5 Based on the working principle the torque output of two stroke engines is higher than those of four stroke engines with the same displacement. VD BMEP T2 Stroke 100 [Nm] 2 Equation 1.1: Torque output of two stroke engines [7] VD BMEP T4 Stroke 100 [Nm] 4 Equation 1.2: Torque output of four stroke engines [2] VD.... displacement [dm 3 ] BMEP. brake mean effective pressure [bar] In Table 1.2 a comparison of the maximum BMEP output of selected naturally aspirated two stroke and four stroke engine applications is pictured. BMEP [bar] Two stroke Four stroke Moped Hand held tools Motorcycle Racing motorcycle Passenger car Racing car Table 1.2: Max. BMEP comparison of naturally aspirated spark ignition engines [3] Beside the higher torque output, based on the working principle, the production costs of two stroke engines are advantageously lower than of four stroke engines. This fact is based on the lower number of moveable parts and the simpler engine structure. But the use of high-tech injection systems, exhaust gas after treatment configurations and acoustic protection proceedings, which have to be installed to fulfill the sophisticated demands of the latest and future regulations, rise the production costs of two stroke engines in the area of four stroke engine manufacturing expenditures

6 Development strategies: Two stroke- or four stroke technologies to drive two wheeler vehicles? An assessment of development tendencies for small capacity engines has to distinguish between engine classes with a displacement of up to 50cc and the classes with a displacement of more than 50cc. In the last years four stroke technologies entered the market in all engine categories above 50cc displacement. The big advantages of two stroke concepts, the high performance output and the relative low production costs, which have convinced over decades, loose more and more their weight because of stricter exhaust gas emission regulations and changed customer demands. The high engine speed levels, achieved by state of the art four stroke engines, compensate their lower torque output, based on the working principle, and lead to respectable power characteristics. Even the motorcycle racing circus changes the rules in several competition classes in favor of race bikes driven by four stroke engines. The top of the range GP1 motorcycle grand prix class introduced a new regulation four years ago, which allows the competition of race bikes driven by 500cc two stroke engines and 990cc four stroke engines. Of course, since the first year, the racers who bed on the four stroke technology, had the better cards. Today, four years later, no race bike driven by a two stroke engine can be found in the front placements of the GP1 competition. In other motor sport classes, does not matter if they are on-road or offroad competitions, the tendency follows the preference of the four stroke technology. Hopefully, new ideas and new technologies will lead to a new and environmentally friendly two stroke engine generation, which enables a return of two stroke technologies into the big capacity motorcycle classes. Away from the motor sport world, new four stroke engine generations started their triumphant advance from Japan in the seventies. Amazing motorbikes, driven by inline four stroke engines from Honda (CB-series) or Kawasaki (Z-series), entered the markets around the world and pushed out the old fashioned two stroke engine driven vehicles. Modern four stroke engines reach extremely high engine speed levels. The 600cc super sport category should serve as an example: The inline four cylinder mass production engines achieve incredible rpm and a specific power output of 165kW/l in the racing setup (Yamaha R6 race bike). Mass production super bike motorcycles with 1000cc displacement, as bought from the dealer for a price of a small car, produce a maximum power output of more than 125kW at rpm, and that by fulfilling all the homologation conditions (Kawasaki ZX-10). In the engine classes with a maximum displacement of 50cc the requirements differ basically. The limited engine capacity has a favorable effect on the two stroke engine concepts, because of their high torque output. Two stroke racing engines in the 50cc class reach a maximum power output of respectable 12kW at rpm (France 50cc Road Racing Series), whereas modern 50cc four stroke racing engines are able to achieve about 8kW at rpm (Japanese 50cc four stroke competition). In homologated vehicles the situation is comparable. Scooters driven by two stroke engines show a favorable drivability and acceleration behavior because of the advantageous torque characteristics. Even in the homologated European version with 45km/h top speed a modern scooter driven by a two stroke engine equipped with direct fuel injection, reaches a maximum power output of 3.5kW at 8.000rpm (Gilera Runner, Euro II homologation)

7 This performance characteristic guarantees an excellent acceleration behavior in comparison with a vehicle driven by a four stroke engine (Piaggio Zip4, Euro II homologation, maximum power output: 2.6kW at 8.000rpm). On European markets the most of the sold mopeds are driven by two stroke engines by far. The trend goes to upgraded power units equipped with direct fuel injection systems in combination with catalytic exhaust gas after treatment strategies. Four stroke engines are offered in a minor number of vehicles nowadays in Europe. No question, the driving performance competition goes to the two stroke technologies, but the emission behavior, respectively the potential to fulfill the requirements of future emission regulations, is another story. Future exhaust emission regulations will include cold start test cycles and a strict reduction of harmful exhaust emission components in combination with on board diagnostic- and durability instructions. These demands lead to the introduction of electronic engine management systems in combination with efficient exhaust gas after treatment concepts into the 50cc engine classes, as well in two stroke engine applications as in four stroke engine applications. Two stroke engines will change from low tech- low cost concepts to upgraded high tech power units equipped with cost intensive fuel injection systems, which rises the production costs up to levels as only known from four stroke engines. The high requests on the emission behavior will reduce the maximum power output level of two stroke engines because the consideration of the cold start emissions will lead to a further prevention of fuel losses during the scavenge process. In any case, the differences in the production costs and the drivability performance between two stroke- and four stroke engine concepts will become smaller in the near future. Technology: System: Advantages: Disadvantages: Future potential: Two valve air cooled with exhaust gas after treatment Four valve water cooled with exhaust gas after treatment Two valve / four valve air or water cooled with electronic fuel injection and oxidation catalyst Supercharged two valve / four valve water cooled with electronic fuel injection and oxidation catalyst Two valve / four valve air or water cooled with electronic fuel injection, closed loop engine management system and 3 way catalyst Supercharged two valve / four valve water cooled with electronic fuel injection, closed loop engine management system and 3 way catalyst Carburetor, catalytic converter and / or secondary air Carburetor, catalytic converter and / or secondary air Electronic fuel injection system, catalytic converter and / or secondary air Electronic fuel injection system, catalytic converter and / or secondary air Electronic fuel injection system, sensor, catalytic converter and / or secondary air Electronic fuel injection system, sensor, catalytic converter and / or secondary air Well developed technology, low fuel consumption, customer friendly maintenance Good performance, well developed technology, low fuel consumption, customer friendly maintenance Low exhaust gas emission level High power output, favorable torque characteristics, low exhaust gas emissions Very low exhaust gas emissions High power output, favorable torque characteristics, very low exhaust gas emissions Low performance Lower performance than two stroke engine technology Lower performance than two stroke engine technology, higher production costs Production costs in comparison with conventional (not supercharged) concepts Lower performance than two stroke engine technology, higher production costs Production costs in comparison with conventional concepts Table 1.3: 50cc four stroke technologies in comparison Potential for future regulations regarding HC and particulate exhaust gas emissions Potential for future regulations regarding HC and particulate exhaust gas emissions Good potential for future emission regulations Good potential for future emission regulations High potential for future emission regulations High potential for future emission regulations - 7 -

8 The potential of different technologies regarding future exhaust emission regulations can be discussed on the basis of the specific characteristics and their effects on the emission output. A new generation of emission regulations (for two wheeler vehicles) considering cold start and life time behavior started with the begin of 2004 on the Taiwanese market. In Europe a new legislation is planned for 2007, and other key markets will follow soon. Cold start test cycles challenge two stroke technologies because they consider the emission output during the light-off phase of the catalytic after treatment system. Due to this fact, the untreated scavenge losses of two stroke engines influence the measurement results in homologation cycles significantly, meaning that they have to be minimized. This situation leads to complex demands on conventional two stroke concepts, because the typical scavenge losses have to be reduced with the help of adjusted port timing, improved scavenge processes and / or direct fuel injection including optimized mixture preparation strategies. Two stroke engines with carburetor technology as used today will have problems to meet future regulations, which include cold start, if the limiting values and the test cycle are similar to the existing ECE R47 homologation cycle. Due to the fact, that scavenge losses are not preventable during the cold start phase, this technology would need far reaching modifications regarding the scavenge control and the scavenge process. Four stroke engines with carburetor technology are able to meet future regulations due to the fine cold start behavior, but only if the CO values are moderately limited and the lean engine setting enables a satisfying drivability of the vehicles. Four stroke engines with fuel injection technology will have no problems to fulfill future emission regulations including cold start. Electronic fuel injection is standard in automotive applications, whereas the resulting technological and economical synergetic effects support an implementation into small capacity engine classes. Catalytic converters in two stroke engines have to be placed carefully in the exhaust system to keep their influence on the gas dynamic effects to a minimum. As known from car engines, the catalyst can be placed near to the cylinder head to shorten the light-off time and thus to improve the cold start behavior in four stroke engine applications additionally. Considering that further steps of exhaust emission regulations within the next years will lead to a further lowering of the permitted emission levels, four stroke engines with closed loop controlled fuel injection systems in combination with three way catalytic systems seem to be a future proof technology for a wide field of applications. Two stroke engines with direct injection systems are able to fulfill the requirements of future emission regulations based on cold start, because of the possibility to prevent fuel scavenge losses

9 Technology: System: Advantages: Disadvantages: Future potential: Standard two stroke engines with exhaust gas after treatment Indirect fuel injection system FAST direct injection system (FAST = Fully Atomized Stratified Turbulence [4]) ASDI Synerject direct injection system (ASDI = Air assisted Synerject Direct Injection [5]) High pressure direct fuel injection systems Carburetor and catalytic converter Fuel injection into the intake manifold, the crankcase or the scavenge ports, catalyst Air compressor FAST, carburetor, catalytic converter Air compressor, direct injection managed by ECU, electronic engine and fuel management system, catalytic converter High pressure fuel injection valve, managed by ECU, electronic engine and fuel management system, catalytic converter Well proved technology, easy to maintenance Relative simple and well proved technology, small modifications on existing engine concepts Good performance, good mechanical durability, low fuel consumption Good performance, very low exhaust gas emissions and very low fuel consumption Good performance, very low exhaust gas emissions and low fuel consumption Poor performance in a throttled version, high fuel consumption Poor performance in a throttled version, problems in a cold start driving cycle Limited Possible application in different classes Drivability, cold start problems, expensive Possible application in maintenance, doubtful different classes potential for future exhaust emission regulations High production costs, expensive maintenance Still in developmental phase, high production costs, expensive maintenance Table 1.4: 50cc two stroke technologies in comparison High potential for future emission regulations High potential for future emission regulations Fuel direct injection systems for two stroke- and four stroke engines In the engine classes up to 50cc displacement two stroke engines with fuel direct injection systems have good chances on the market because of the favorable power - weight ratio in comparison with conventional four stroke engines under the conditions of a medium term emission legislation. A disadvantage of this high technological two stroke engines are the production costs, which lie significantly above the production costs of low tech engines (Table 1.5). The increase of manufacturing costs with the implementation of new technologies (FAST, ASDI, etc.) and the more intensive development expenditure will lead to a higher price level on the market. A trend in the opposite direction comes from Asian manufacturers, where the production costs are on a lower level than in Europe. Asian products combined with modern technologies are able to hold or to lower the prices on the market even under the boundaries of future exhaust gas regulations. In any case, it will take a strict optimizing philosophy and the use of cooperation strategies across the product range to keep the cost structure in the production of small two stroke engines competitive in comparison with the costs of small four stroke engine production. Fuel direct injection systems for four stroke engines will not enter the field of the 50cc class in the next time, but it is imaginable that these systems could be implemented in high performance motorcycle engines in the upper capacity classes

10 The development of direct injection systems for four stroke engines include high pressure fuel pumps, common rail, injection nozzles, pressure control units, etc. The know how from the supplier of the car industry can help to accelerate the development of this application for the use in motorcycles. The indirect fuel injection into the intake manifold was and will be the competitor of direct injection concepts. An expected increase of 5-10% power output and the decrease of about 3-5% fuel consumption will not be honored by the scooter- and motorcycle customers as in automotive applications. An exception could represent the racetrack derived sport motorcycle classes, in which the improved engine performance is a buyer s argument. Four stroke engine concepts with indirect fuel injection systems are realizable in short development times because the application of these systems in different capacity classes is well approved and supported by a big number of suppliers Comparison of the production costs of different 50cc engine technologies The table below lists a production costs comparison of different technologies in the 50cc engine class. The calculation is based on an output target of units per year and considers the costs for the complete power unit, as used in scooter applications including the swing arm, the transmission unit and the exhaust system made of stainless steel including a catalyst. The production cost calculation bases on data from an Asian engine manufacturer, whereas the injection system expenditure is calculated by an European supplier. 50cc engine technology Cost difference [%] Standard two stroke engine with carburetor Two stroke engine with fuel injection system D.I. two stroke engine with carburetor (FAST - System) D.I. two stroke engine with fuel injection system (Synerject) High pressure D.I. two stroke engine Four stroke engine with carburetor Four stroke engine with fuel injection system 0% 40% 48% 64% 79% 70% 102% Table 1.5: Comparison of the production costs of different engine concepts Standard two stroke engine with carburetor: Air cooled two stroke engine with carburetor and catalytic converter; emission target potential: Euro II

11 Two stroke engine with fuel injection system: Water cooled two stroke engine with indirect low pressure fuel injection system; emission target potential: Euro III D.I. two stroke engine with carburetor based inner mixture preparation (FAST System): Water cooled two stroke engine with the air assisted direct injection system from Piaggio (FAST); emission target: Euro II D.I. two stroke engine with fuel injection system (Synerject): Water cooled two stroke engine with the air assisted direct injection system from Synerject (inner mixture preparation supported by F.I.), emission target potential: Euro III and further High pressure D.I. two stroke engine: Water cooled two stroke engine with high pressure direct injection system; emission target potential: Euro III and further Four stroke engine with carburetor: Water cooled four stroke engine with carburetor; emission target potential: Euro III Four stroke engine with fuel injection system: Water cooled four stroke engine with fuel injection system (intake manifold); emission target potential: Euro III and further All the described engine technologies are able to fulfill the Euro II emission targets. With the introduction of more severe exhaust emission limits in the next years in combination with advanced test procedures (cold start, durability, etc.) two stroke engines, equipped with conventional carburetor technologies, will have problems to meet the requirements, but two stroke engine concepts in combination with direct injection systems are able to stay competitive. In the future, an approach of the two wheeler exhaust emission regulations into the region of automotive legislations is thinkable. On the basis of these regulations the implementation of automotive technologies can take place in two wheeler applications, which will favor the four stroke technology above the two stroke technology, because of the possibility to use a sensor based engine control in combination with a three way catalyst. The implementation of a closed loop engine control system including a sensor and a 3 way catalytic converter (instead of an oxidation catalyst) rises the production cost listed in Table 1.5 about 10% Development steps in the two wheeler industry in the next years Two stroke engine technologies: Reduction of the two stroke scavenge losses with the help of optimized scavenge processes, injection systems and variable exhaust timing adjustment

12 Lean burn concepts: Engine operation with > 1 Adjustable internal exhaust gas recirculation by variable scavenge geometries Optimized lubrication of the crank train to reduce the oil consumption and the particulate emissions Variable port timing Variable scavenge flow characteristics Cold start strategies, improved exhaust gas after treatment systems Extended durability of the exhaust gas after treatment systems Combined exhaust gas after treatment systems Four stroke engine technologies: Variable valve timing Defined charge flow variation Supercharging concepts Fuel injection intake manifold Optimization of engine friction Cold start strategies, improved exhaust gas after treatment in combination with closed loop engine management systems Extended durability of the exhaust gas after treatment systems Combined exhaust gas after treatment systems Alternative driving concepts (under discussion): Electric vehicles Alternative fuels Hybrid concepts Compressed air driven power units Drive train: Efficiency improvement of CVT systems Semi-automatical transmissions New transmission concepts in combination with new engine concepts (hybrid concepts) Hybrid engine concepts, electric two wheeler vehicles Hybrid engine technologies (internal combustion engines combined with electric generator / engine units) have been developed to reduce exhaust gas emissions, to save fuel and to satisfy green leaned impulses of some governments. Different concepts, which have been introduced for automotive applications, are not directly transferable into two wheeler applications (with small displacement engines), because the fundamental requirements on driving units for two wheeler urban

13 vehicles are not the same as on car- or truck applications. Beside a high performance density and a lightweight structure, low production costs and a customer friendly handling, the power units have to find place in the restricted space of scooter bodies. Whereas the performance characteristics of electric motors seem to be appropriate for the use in small motorcycles, the heavy and space consuming batteries challenge the development of new technologies. [6] Today s hybrid- or electric engine concepts are not able to compete with conventional internal combustion engines, but in the future very strict emission regulations in congested areas can lead to market niches, in which these concepts are able to proof a low noise and environmentally friendly alternative to the well known combustion engine technologies. In large Asian cities, especially in its centers, electric driven scooters are well accepted as personal movement possibility beyond the daily rush hour scenarios

14 2. ENGINE TECHNOLOGIES IN THE 50cc CATEGORY Four different engine concepts give an overview of the applied engine technologies in the treated capacity category. Three vehicles driven by four stroke engines and one vehicle driven by a high technology two stroke engine will be introduced in the following chapter. PIAGGIO ZIP4 Fig. 2.1: Scooter Piaggio Zip4 The Zip4 produced by the big Italian manufacturer Piaggio is a middle class scooter for European markets. To consider more strict exhaust emission legislations and the demands of ecology minded customers Piaggio equips this scooter with a four stroke engine. The Piaggio Zip4 is placed on the market as environment friendly alternative to the well known Zip2 models which are driven by fan cooled 50cc two stroke engines with carburetor technology and oxidation type catalytic converter. Both, the Zip4 and the Zip2, have the same chassis and only distinguish between the engine concepts. The Zip4 is driven by a 50cc four stroke engine with carburetor technology. The two valve engine with a bore of 39mm has a chain driven single overhead camshaft and rocker arms. The crankshaft is a build type and runs on roller bearings. The lower end of the con rod runs on needle bearings whereas the upper end holds the piston pin directly. A conventional four stroke piston made of aluminum with two compression rings and one oil scraper ring is guided by a NiCaSil plated aluminum cylinder. The engine lubrication is forced by a tooth wheel oil pump placed in the oil pan. The air cooling system is forced by a fan on the crankshaft. The build up of the drive train is similar to them of drive trains with two stroke engines including a conventional CVT and a two step secondary transmission. The engine is equipped with an electric starter and a kick start mechanism (helps if the battery is empty). The complete engine design is influenced by a low cost strategy to keep the cost difference between the Zip2 scooter (two stroke engine) and the Zip4 scooter (four stroke engine) in acceptable ranges. Figure 2.3 illustrates the engine design with the help of three sectional drawings and Table 2.1 includes the technical data of the drive unit

15 The performance characteristic of the Piaggio Zip4 engine is shown in Figure 2.2. The low cost four stroke engine concept is not able to compete with conventional two stroke engines (carburetor technology) regarding torque behavior and maximum power output. As result the acceleration of the Zip4 is poor in comparison with the Zip2 or other scooter driven by conventional air cooled two stroke engines. Anyway, this engine represents a user friendly drive unit (no refilling of two stroke oil necessary) for customers with green leanings and no high demands on the power output. Engine: 1 cylinder, four stroke Bore x stroke [mm]: 39 x 41.8 Displacement [cc]: 49.9 Compression ratio [-]: 11.5 : 1 Max. power output [kw]: 2.64 At engine speed [rpm]: 8000 Max. torque output [Nm]: 3.15 At engine speed [rpm]: 7000 Valve train: Cooling system: Carburetion system: Lubrication system: Two valve, SOHC, chain drive Forced air Multi jet carburetor Trochoidal pump Transmission: CVT, centrifugal clutch, secondary transmission: 2 step gear Table 2.1: Technical data of the Piaggio Zip4 engine power [kw] engine power engine torque torque [Nm] engine speed [rpm] 0.0 Fig. 2.2: Power- and torque characteristics of the Piaggio Zip4 engine

16 Fig. 2.3: Drawings of the Piaggio Zip4 engine

17 HONDA CB50V Fig. 2.4: Motorbike Honda CB50V Dream The CB50V Dream is an anniversary model from Honda and has been presented 1997, whereas a small number has been sold in Europe for about Euro 4000,- per unit. The design of the limited edition bases on the famous Honda CR110 (built from 1963 to the late sixties), which is one of the most successful race motorbikes ever. The CR 110 was Hondas first general purchasable Production Racer. The high reliability and the revolutionary design made the one cylinder 50cc four stroke engine with DOHC and four valve cylinder head hard to beat. In the Grand Prix setup a power output of up to 8.5kW at rpm pushed the racer to a high speed of more than 133km/h (Isle of Man, 1964). A big number of famous racing driver triumphed with the CR 110, alone George Ashton won 485(!) documented first places with this motorbike during his carrier. The engine is build in the Honda Dream 50R too, a popular retro styled motorbike available on the Japanese market. Special brand race series with the CB50R lead to a small but intensive engine tuning scene in Japan, whereas the expected maximum power output of modified engines should reach more than 6kW at rpm. Anyway, the original (homologated) Honda CB50V Dream reaches 3.25kW at rpm engine speed, which seems to be a good value for a 50cc four stroke engine. According to the Japanese legislation the maximum speed of the vehicle is restricted to 60km/h (electronic restriction in the 6 th gear). The relative wind cooled motorcycle engine is combined with a foot shifted 6 speed transmission. As secondary drive works a roller chain. The engine body made of aluminum is fixed in the vehicle frame with three bolted connections. The four valve cylinderhead contains two overhead camshafts and tappets. The camshafts run on plain bearings and are driven by a low noise inverted tooth type chain in combination with a central gear. The crankshaft is a build type with roller bearings, and the con rod lower end runs on a needle bearing. This bearing concept guarantees low friction and is easy to lubricate. The oil pump driven by a gearwheel from the crankshaft is placed in the oil pan and supplies the crank train and the valve train. As usual in motorbike engines the splash lubricated transmission is connected to the engine block directly

18 The relative wind cooling concept leads to characteristic fins on the cylinder head and the cylinder, which let the engine appear bigger than the 50cc displacement expect. With the help of two section cuts Figure 2.5 makes the technology of the CB50V engine visible. In Table 2.2 the technical data are listed. Engine: 1 cylinder, four stroke Bore x stroke [mm]: 40 x 39.2 Displacement [cc]: Compression ratio [-]: 10.9 : 1 Max. power output [kw]: 3.25 At engine speed [rpm]: Max. torque output [Nm]: 3.17 At engine speed [rpm]: 9000 Valve train: Cooling system: Carburetion system: Lubrication system: Transmission: Four valve, DOHC, chain drive Relative wind Kehin CV, 22mm Venturi diameter Trochoidal pump 6 speed gear, secondary drive: chain Table 2.2: Technical data of the Honda CB 50V engine Fig. 2.5: Drawings of the Honda CB 50V engine

19 The performance characteristics of the Honda CB50V engine is shown in Figure 2.6. The complete engine layout is oriented to reach high engine speeds, and so even the homologated engine runs about rpm. The torque curve shows a flat progression between 6000rpm and rpm, but the level is not high (3.17Nm at 9000rpm), what is typical for a racing engine. The remarkable maximum power output at rpm and the speed reserve of about 2000rpm to the speed limiter points to the high potential of the engine. power [kw] torque [Nm] engine power engine torque engine speed [rpm] Fig. 2.6: Power- and torque characteristics of the Honda CB 50V engine HONDA CREA SCOOPY Fig. 2.7: Scooter Honda Crea Scoopy Honda offers a big family of scooters driven by 50cc four stroke engines on the Japanese market. The Crea Scoopy is a popular urban vehicle driven by the latest engine generation, which is available with carburetor technology or an electronic fuel injection system

20 The engine design is influenced by the long standing experience of Honda in small four stroke engine development: A very smart and low cost engine build up in combination with the latest technology leads to the probably best engine in this class. The low friction bearing strategy of crank- and valve train in combination with the pump forced oil cycle guarantees a long durability and a customer friendly operation. The two valve cylinder head with a chain driven over head camshaft and rocker arms also includes the pump for the liquid cooling cycle. The radiator is placed on the side of the crankcase, whereas a flywheel driven fan forces a cooling airflow. The build type crankshaft drives the oil pump in the oil pan with the help of a gearwheel made of plastic. As usual in this engine category the con rod lower end runs on needle bearings whereas the upper end holds the piston pin directly. The aluminum piston equipped with two compression rings and one oil scraper ring is guided by a gray cast iron insert in the aluminum cylinder. Engine: 1 cylinder, four stroke Bore x stroke [mm]: 38 x 44 Displacement [cc]: 49.9 Compression ratio [-]: 12 : 1 Max. power output [kw]: 2.96 At engine speed [rpm]: 8030 Max. torque output [Nm]: 3.87 At engine speed [rpm]: 6780 Valve train: Cooling system: Carburetion system: Lubrication system: Two valve, SOHC, chain drive Liquid Kehin constant pressure carburetor, 18mm Venturi diameter Trochoidal pump CVT, centrifugal clutch, secondary Transmission: transmission: 2 step gear Table 2.3: Technical data of the Honda Crea Scoopy engine As special detail the cylinder and the crankcase upper part are designed as mono block (one part). The build up of the drive train is similar to them of drive trains driven by two stroke engines including a conventional CVT and a two step secondary transmission. The engine is equipped with an electric starter and a kick start mechanism. Figure 2.8 illustrates the engine design and Table 2.3 includes the technical data of the drive train. Figure 2.9 shows the performance characteristics of the Crea Scoopy engine. A flat torque curve progression with its peak (3.87Nm) at 6780rpm leads to a driver friendly engine behavior. A maximum power output of about 3kW shows the thermodynamic potential of the engine. The maximum speed of the vehicle is limited to 60km/h according to the Japanese legislation. The two valve concept in combination with the relative small bore (38mm) and a limited engine speed of 8750rpm states a position with good prospects

21 Fig. 2.8: Drawings of the Honda Crea Scoopy engine

22 power [kw] torque [Nm] engine power engine torque engine speed [rpm] Fig. 2.9: Power- and torque characteristics of the Honda Crea Scoopy engine APRILIA SR50LC DITECH Fig. 2.10: Scooter Aprilia SR 50LC DiTech The Italian manufacturer Aprilia offered its top of the range model in the 50cc scooter class with a water cooled two stroke engine in combination with an electronic air assisted direct fuel injection system since Apart from a few more or less successfully experiments with direct fuel injection systems in this small capacity engine category (for example the short available Piaggio FAST in the late nineties) the air assisted injection system from Synerject can be seen as the only satisfying concept for 50cc scooter engines (at 2004). Since 2003 some other manufacturers (Piaggio, Derby, Peugeot) equip their top models with a similar system

23 With the help of this injection system two stroke engines are able to reach strict exhaust emission regulations and to provide a remarkable performance characteristic at the same time. Beside this technology, some new ideas are in developing status this time. Dr. Kirchberger s presentation treats different technologies in two stroke applications in detail. So this publication will not go into detail, the impact on the emission characteristics will be discussed in the following chapters. Engine: 1 cylinder, two stroke Bore x stroke [mm]: 41 x 37,4 Displacement [cc]: Compression ratio [-]: 12.5 : 1 Max. power output [kw]: 4.78 At engine speed [rpm]: 8000 Max. torque output [Nm]: 5.80 At engine speed [rpm]: 7500 Cooling system: Carburetion system: Lubrication system: Liquid Synerject air assisted direct injection system, 18mm throttle body Electronic two stroke oil pump Transmission: CVT, centrifugal clutch, secondary transmission: 2 step gear Table 2.4: Technical data of the Aprilia SR 50 DiTech engine The principle of the fuel injection process bases on compressed air, which is used to assist the atomization of fuel injected directly into the combustion chamber, facilitating very fine control of the air fuel gradient around the spark plug. Direct injection into the chamber (typically after transfer and exhaust ports have closed) also more effectively eliminates short circuiting of fuel than is possible with manifold and port fuel injection concepts. In comparison with single fluid systems the air assisted injection concept has advantages because of the lower system pressures, the smaller fuel particle size and the better distribution. Figure 2.11 illustrates the power and torque characteristics of the Aprilia SR50LC DiTech engine. In comparison with conventional four stroke engine concepts the curve progression shows the remarkable high performance output based on the two stroke principle

24 power [kw] torque [Nm] 2.0 engine power engine torque engine speed [rpm] Fig. 2.11: Power- and torque characteristics of the Aprilia SR 50 DiTech engine Fig. 2.12: System schematic of the air assisted direct fuel injection system from Synerject

25 Fig. 2.13: Drawings of the Aprilia SR 50 DiTech engine

26 3. POTENTIAL OF THE 50CC TWO WHEELER MOTOR VEHICLE CLASS IN RESPECT OF FUTURE EXHAUST EMISSION TARGETS Future emission regulations for two wheeler vehicles driven by small capacity engines will include the cold start characteristics and the durability behavior. [1] Based on the European homologation cycle ECE R47 and an additional cold start test cycle, a number of scooters driven by 50cc engine concepts in combination with different exhaust gas after treatment strategies have been analyzed and evaluated. The test series have been performed with the help of a CVS measurement system according the European homologation instruction and in addition with the help of an online emission recorder measurement. 3.1 MEASUREMENT PROCEDURE The exhaust emissions of selected vehicles have been measured on a chassis dyno with a constant volume sampling (CVS) for diluted exhaust emission measurement according to the European ECE R47 homologation demands. In addition, the time dependent characteristics of the exhaust emission components have been online recorded during the complete test cycle. The online measurement allows to research the progression of the hydrocarbon- (HC) the nitrogen- (NOx) and the carbon monoxide (CO) exhaust emissions during acceleration and deceleration phases of the vehicles in the measurement cycles and gives detailed information about the exhaust emission characteristics of the different concepts. To analyze the power unit concepts in reference to future exhaust emission regulation which include the warm up phase the vehicle testing has been carried out with the help of two test cycles: 1. European homologation cycle ECE R47, a valid test cycle with limiting values of 1 g/km for CO and 1.2 g/km for HC+NOx emissions (Figure 3.1) [7] 2. Cold start cycle as test cycle which includes the warm up characteristics According to the European Standard the vehicle mass has to be considered on the chassis dyno, whereas the reference weight is calculated as summation of the vehicle weight plus 75 kg 5kg tolerance. With the reference weight, the road resistance is defined by a rear wheel power output at a vehicle speed of 50 km/h to compare the miscellaneous vehicles on the chassis dyno

27 Figure 3.1: European homologation cycle ECE R47 according the EURO II exhaust emission measurement standards HOMOLOGATION CYCLE The European homologation cycle (Figure 3.1) for mopeds with a displacement of maximal 50cc and a maximum vehicle speed of 45km/h consists of eight identical cycles that are composed of a full load section and a part load section. At the beginning of each full load section the throttle position (100%) is held constant until the start of the deceleration phase. At this point the throttle must be closed (0%) and kept close during the deceleration phase down to 20 km/h vehicle speed; reducing the speed by braking is allowed, if the vehicle exceeds the deceleration line. After meeting the 20km/h point, the vehicle speed is held constant until the next deceleration phase. During the homologation test the first four cycles serve as warm up phase. The actual exhaust gas measurement procedure starts at the beginning of the fifth cycle, whereas the exhaust gas of the last four cycles is sampled and analyzed. COLD START CYCLE To study the cold start characteristics a modified test cycle based on the ECE R47 homologation cycle has been created (Figure 3.1), in which the cold start enrichment of the carburetion systems and the light off timing of the exhaust gas after treatment systems are considered. After starting the engine the measuring procedure begins immediately within 8 seconds but always before the first acceleration phase of the homologation cycle. To get comparable results, the measuring time is the same as in the homologation cycle. This means that the exhaust gas of the first four cycles is sampled and analyzed. The evaluation of the warm start and the cold start

28 measurement series of each inspected test vehicle points to exhaust emission characteristic based on the specific concepts. The time dependent detection of the HC, CO and NOx emission progression with the help of a recorder system allows a detailed discussion of the untreated and treated emission behavior of the different engine types and their cold start strategies. In addition, the progression of the emission components as function of time gives information about response and the efficiency of the exhaust gas after treatment systems. 3.2 RESEARCHED ENGINE- AND EXHAUST GAS AFTER TREATMENT CONCEPTS The measurement schedule contains vehicles with two stroke and four stroke engine concepts, both equipped with carburetor and electronic fuel injection systems combined with different exhaust gas after treatment applications. To compare similar drive train concepts all the treated vehicles are scooters equipped with a constant velocity transmission (CVT) in combination with a secondary gear. RESEARCHED ENGINE- AND EXHAUST GAS AFTER TREATMENT CONCEPTS Test vehicle 1: Test vehicle 2: Test vehicle 3: Test vehicle 4: Test vehicle 5: Test vehicle 6: Test vehicle 7: Two stroke engine with carburetor Two stroke engine with carburetor and oxidation catalyst Two stroke engine with carburetor, secondary air system, coated exhaust muffler and oxidation cat. Two stroke engine with air assisted direct injection system and oxidation catalyst Four stroke engine with carburetor and secondary air system Four stroke engine with carburetor, secondary air system and oxidation catalyst Prototype four stroke engine with fuel injection Test vehicle 8: Prototype four stroke engine with FI, secondary air system and oxidation catalyst Table 3.1: Survey of the measured vehicle configurations Four different scooters with two stroke engines have been analyzed: One representative vehicle with carburetor and oxidation catalyst, one with carburetor plus secondary air system in combination with a coated muffler plus an oxidation catalyst and one vehicle with the latest air assisted direct injection system in combination with an oxidation catalyst. In addition the first vehicle has been measured without a catalyst to compare the behavior of the untreated and the treated exhaust gas progression

29 All these scooters with two stroke engines, except for the vehicle without a catalyst, are new mass production vehicles (year of production: 2003), homologated according to the European EURO II legislation and measured in the original state as bought from the dealer. The studies of scooters with four stroke engines are based on two different vehicles: The first is a state of the art scooter from the Japanese market (year of production: 2003), which is measured first in its original configuration and then with a modified exhaust gas after treatment. The Japanese and the European exhaust gas emission regulations are different in the driving cycle and in the limited values and consequently not direct comparable. It has to be stated, that the carburetor setting of the test vehicle has not been optimized for the European driving cycle. This is the reason why the measurement results are not directly comparable with the results of the two stroke engine driven vehicles. The measurement series are carried out to show the potential of four stroke engines in this small capacity class and to point out the influences of different exhaust gas after treatment concepts. The second basic vehicle with a four stroke engine is driven by a supercharged prototype engine with a fuel injection system. TEST VEHICLE 1 AND 2: A vehicle driven by an air cooled two stroke engine with carburetor in combination with an oxidation catalyst has been chosen as representative for the low cost scooter category. The technical data and the measurement results of the test vehicle 1 (modified vehicle 2) are listed in Table 3.2. Test vehicle 1: Prototype two stroke engine with carburetor Engine type Carburetion system Cooling system Two stroke Slide carburetor with 16mm diameter Forced air Exhaust gas after treatment - Cold start system Transmission Vehicle reference mass Mean fuel consumption in the homologation cycle Thermo switch choke CVT, secondary gear 150 [kg] 32.7 [km/l] Homologation - Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle CO: HC+NOx: CO: HC+NOx: 3.06 [g/km] 4.80 [g/km] 2.79 [g/km] 5.69 [g/km] Table 3.2: Technical data and measurement results of test vehicle 1 To study the influence of the oxidation catalyst on the exhaust emission characteristics in general and the cold start behavior in detail, a second measurement series without the catalyst has been performed. For that purpose the original catalytic converter has been exchanged by a non coated metallic catalyst

30 carrier to measure the untreated exhaust gas emissions. This procedure has been carried out to keep the counter pressure situation in the exhaust system similar as possible to the original configuration. The changed gas dynamic effects, due to the lower temperature levels in the exhaust system have not been considered. All the other parts of the engine, the exhaust system and the transmission have not been modified. The technical data of the mass production test vehicle 2 and the measurement results are listed in Table 3.3. Test vehicle 2: Two stroke engine with carburetor and oxidation catalyst Engine type Carburetion system Cooling system Exhaust gas after treatment Cold start system Transmission Vehicle reference mass Mean fuel consumption in the homologation cycle Homologation Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle Two stroke Slide Carburetor with 16mm diameter CO: HC+NOx: CO: HC+NOx: Forced air Oxidation catalyst Thermo switch choke CVT, secondary gear 150 [kg] 36.6 [km/l] Euro II 1.04 [g/km] 0.67 [g/km] 2.48 [g/km] 3.03 [g/km] Table 3.3: Technical data and measurement results of test vehicle 2 TEST VEHICLE 3: Test vehicle 3: Two stroke engine with carburetor, secondary air system and oxidation catalyst Engine type Carburetion system Cooling system Exhaust gas after treatment: Cold start system Transmission Vehicle reference mass Homologation cycle fuel consumption Homologation Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle Two stroke Slide carburetor with 17.5 mm diameter Liquid Secondary air, pre catalyst and oxidation catalyst CO: HC+NOx: CO: HC+NOx: Thermo switch choke CVT, secondary gear 170 [kg] 25.5 [km/l] Euro II 1.55 [g/km] 3.25 [g/km] 4.25 [g/km] 8.30 [g/km] Table 3.4: Technical data and measurement results of test vehicle

31 The test vehicle 3 (Table 3.4) is driven by a liquid cooled two stroke engine with carburetor. In comparison to the test vehicle 2, the exhaust gas after treatment is performed by a secondary air induction and a dual catalyst system, which consists of a catalytic coated exhaust manifold combined with an oxidation catalyst. TEST VEHICLE 4: The forth test vehicle is driven by a two stroke engine with a more complex carburetion concept: An air assisted direct injection system pre-mixes fuel and compressed air in a chamber. The injection of this mixture into the combustion chamber is controlled by an electromagnetic valve. This procedure enables a favorable fuel mixture generation in combination with exactly controllable injection timing. Direct injection into the combustion chamber enables more effective elimination of fuel short circuiting than it is possible with conventional carburetion concepts. In addition to the advantages in the exhaust emission characteristics and in the fuel consumption, the test vehicle 4 shows a good performance behavior and drivability. Table 3.5 includes the technical data and the measurement results of test vehicle 4. Test vehicle 4: Two stroke engine with air assisted direct injection system and oxidation catalyst Engine type Carburetion system Cooling system Exhaust gas after treatment Cold start system Transmission Vehicle reference mass Homologation cycle fuel consumption Homologation Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle Two stroke Air assisted direct injection system CO: HC+NOx: CO: HC+NOx: Liquid Oxidation catalyst Thermo switch choke CVT, secondary gear 190 [kg] 40.8 [km/l] Euro II 0.62 [g/km] 1.16 [g/km] 2.71 [g/km] 1.62 [g/km] Table 3.5: Technical data and measurement results of test vehicle 4 Succeeding the study of different two stroke engine concepts combined with exhaust gas after treatment procedures, a number of measurement series with varying four stroke engine configurations have been carried out to assess the potential regarding low emission behavior at satisfying performance characteristics. Four stroke engines are not intensively represented in the 50cc moped category in Europe in this time due to preferable performance characteristics and the low production costs of conventional two stroke engines. The introduction of more severe exhaust emission regulations in this vehicles class may lead to the implementation of advanced motor

32 control units also in two stroke engines (see test vehicle 4) and therefore decreases the advantage in the production costs in comparison with four stroke engines. TEST VEHICLE 5 AND 6: A scooter from the Japanese market driven by a liquid cooled four stroke engine with two valves and an overhead camshaft concept serves as basis for the test vehicles 5 and 6. The setup of this mass production engine has been performed to fulfill the Japanese exhaust emission regulations, leading to a relatively high CO emission level in the European driving cycle. Under these circumstances the results of the measurement series pictured in this paper are able to point to the emission characteristics and emission potential of 50cc four stroke engines but they are not directly comparable with the measurement results of the two stroke engines. For the test series, the general engine setup has not been modified, but the maximum vehicle speed has been restricted to 45km/h (with the help of a stop position in the carburetor) according the ECE R47 regulation. Table 3.6 lists the technical data and the measurement results of test vehicle 5. Test vehicle 5: Four stroke engine with carburetor and secondary air system Engine type Carburetion system Cooling system Exhaust gas after treatment Cold start system Transmission Vehicle reference mass Homologation cycle fuel consumption Homologation Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle Four stroke Constant pressure carburetor, 18 mm diameter CO: HC+NOx: CO: HC+NOx: Liquid Secondary air Thermo switch choke CVT, secondary gear 150 [kg] 49.1 [km/l] Japan 7.92 [g/km] 0.97 [g/km] 7.74 [g/km] 2.13 [g/km] Table 3.6: Technical data and measurement results of test vehicle 5 The test vehicle 5 is equipped with a secondary air system, which induces fresh air into the exhaust port. For a further optimization and to study the emission potential of 50cc four stroke engines combined with carburetor, an oxidation catalyst has been adapted to the exhaust system of test vehicle 5. Table 3.7 lists the technical data and the measurement results of test vehicle 6. With the exception of the catalytic converter, the mass production engine has not been modified, neither the carburetor setup nor the secondary air system. In this way the influence of the oxidation catalyst on the collected emissions and the time dependent emission progression can be studied by comparing the measurement results of test vehicle 5 and test vehicle

33 Test vehicle 6: Four stroke engine with carburetor, secondary air system and oxidation catalyst Engine type Carburetion system Cooling system: Exhaust gas after treatment Cold start system Transmission Vehicle reference mass Homologation cycle fuel consumption Four stroke Constant pressure carburetor, 18 mm diameter Liquid Secondary air + oxidation catalyst Thermo switch choke CVT, secondary gear 150 [kg] 47.4 [km/l] Homologation - Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle CO: HC+NOx: CO: HC+NOx: 2,85 [g/km] 0,24 [g/km] 6.67 [g/km] 0.84 [g/km] Table 3.7: Technical data and measurement results of test vehicle 6 TEST VEHICLE 7 AND 8: Test vehicle 7: Prototype four stroke engine with fuel injection and secondary air system Engine type Carburetion system Cooling system Four stroke Fuel injection system Liquid Exhaust gas after treatment - Cold start system Transmission Vehicle reference mass Homologation cycle fuel consumption ECU Application CVT, secondary gear 150 [kg] 40.1 [km/l] Homologation - Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle CO: HC+NOx: CO: HC+NOx: 1.18 [g/km] 1.99 [g/km] 1.24 [g/km] 2.05 [g/km] Table 3.8: Technical data and measurement results of test vehicle 7 A prototype scooter with a new developed crankcase supercharged 50cc four stroke engine serves as basis for the test vehicles 7 and 8. [8] The carburetion is performed with the help of a conventional open loop low pressure fuel injection system into the intake manifold. Table 3.8 lists the technical data and the measurement results of test vehicle 7. The engine and the transmission of test vehicle 8 are the same as in test vehicle 7, but the exhaust gas after treatment is extended with an oxidation catalyst. There have been no modifications of the injection system application performed. The significant differences in the measurement results are only forced by the effect of the

34 exhaust gas after treatment. Table 3.9 lists the technical data and the measurement results of test vehicle 8. Test vehicle 8: Prototype four stroke engine with FI, secondary air system and oxidation catalyst Engine type Carburetion system Cooling system Exhaust gas after treatment Cold start system Transmission Vehicle reference mass Homologation cycle fuel consumption Homologation Measurement results, ECE R47 homologation cycle Measurement results, ECE R47 based cold start cycle Four stroke Fuel injection system Liquid Secondary air + oxidation catalyst CO: HC+NOx: CO: HC+NOx: ECU Application CVT, secondary gear 150 [kg] 38.7 [km/l] Potential Euro III (cold start) 0,20 [g/km] 0.42 [g/km] 0.40 [g/km] 0.89 [g/km] Table 3.9: Technical data and measurement results of test vehicle 8 The supercharged prototype engine shows a remarkable performance characteristic with a flat torque progression on a high level that leads to a comfortable drivability of the prototype vehicle. The maximum power output is comparable with the power output of modern two stroke engines. [9] 3.3 MEASUREMENT RESULTS RESULTS OF THE CVS MEASUREMENT SERIES The CVS measurement series have been carried out according the European ECE R47 homologation cycle and in addition in the cold start test cycle. Figure 3.2 shows a summary and compares the measured CO- and HC+NOx emissions of all tested vehicles in both cycles. Comparison of two- and four stroke engines with carburetor (test vehicles 1, 2, 3, 5 and 6): The average of the vehicles driven by four stroke engines indicates a less HC+NOx emission output than the average of the two stroke engine driven vehicles with carburetor technology. A comparison of the two stroke- and the four stroke driven test vehicles with carburetor technology but without catalyst (test vehicle 1 and 5) shows the different emission characteristics of these engine concepts: The two

35 stroke engine produces a higher HC+NOx emission level, although the carburetor setting is more lean than them of the four stroke engine (lower CO level of the two stroke engine). The measurement results of test vehicles 2 (compared to test vehicle 1) and test vehicle 6 (compared to test vehicle 5) point to the significant influence of the catalytic exhaust gas after treatment: The output of the HC+NOx emissions decreases about 85% at the two stroke engine- and about 75% at the four stroke engine application whereas the CO emissions decrease about 65% at both engine concepts only by the catalytic effect. In the case of the four stroke engine used in test vehicle 6, which engine setting is not optimized for a catalyst application, a further lowering of the emission level, especially of the CO output is possible. The engine technology of test vehicle 2 is a quite simple and low cost version of a two stroke engine application in a scooter: Carburetor technology in combination with an efficient catalytic conversion in the exhaust system is able to meet the Euro II regulation, provided that the thermodynamic layout and the engine setup are performed carefully. Test vehicle 3 does not reach the Euro II homologation limits. The measurement results show a violation of 270% of the HC+NOx limit and about 155% of the CO limit. A significant increased emission behavior at reduced catalytic conversion in the cold start cycle points to a rich engine setting. Comparison of two- and four stroke engines with fuel injection systems (test vehicles 4, 7 and 8): The measurement results of the sophisticated two stroke engine concept build in test vehicle 4 show respectable emission characteristics in the homologation cycle and under cold start conditions, which base on an effective prevention of the scavenge losses with the help of the injection system combined with an efficient catalytic conversion of the exhaust gases. A comparison of test vehicle 4 and 8 shows that the differences in the emission output between the homologation cycle and the cold start cycle are more significant in case of the two stroke engine. This points to a closer dependency of the two stroke engine concept on the efficiency of the exhaust gas after treatment. Especially the higher CO value (about 440%) in the cold start cycle points to a intensively starting enrichment. The remarkable increase of the CO emissions in the cold start will be discussed in the next chapter based on the results of the recorder measurement. The emission behavior of test vehicle 7, which is driven by a supercharged four stroke engine with a fuel injection system, shows an eye catching characteristic: Whereas the level of the HC+NOx emission is 100% higher than at the test vehicle 5 (four stroke with carburetor technology) the CO emissions are significant reduced for homologation cycle. The small detected difference between the homologation cycle and the cold start cycle is based on a short enrichment strategy of the injection system. Test vehicle 8 represents the obvious upgrade of test vehicle 7. The supercharged four stroke engine with fuel injection system in combination with a secondary air induction and an oxidation catalyst produces the lowest exhaust emission output of

36 all compared engine concepts. The emission levels in the homologation cycle undercut the Euro II limits about 80% (CO emission) and 65% (HC+NOx emissions). In case of the cold start cycle this engine concept is also able to meet the Euro II regulation values with a comfortable distance to the limits

37 Figure 3.2: Summary of the CVS measurement series HC+NOx emission behavior in the homologation cycle and in the cold start test cycle The tested engine concepts in combination with different exhaust gas after treatment strategies show various characteristics regarding their cold start behavior. Exemplary a comparison of the measured HC+NOx emissions in the homologation cycle and in the cold start cycle is illustrated in Figure 3.3. In the cold start cycle the effect of the catalytic exhaust gas after treatment on the HC+NOx emission output is reduced because of the delayed start up of the oxidation catalyst (light off time). In addition the starting enrichment of the carburetion systems leads to an increase of the HC emission in the start phase. Anyway, all tested vehicles show a higher HC+NOx emission output in the cold start cycle than in the homologation cycle. In Figure 3.4 the divergence of the measured HC+NOx emissions between the homologation cycle and the cold start cycle is pictured: With the exception of test vehicle 4 all the measured scooters equipped with an oxidation catalyst (test vehicle 2, 3, 6 and 8) show a high difference in the HC+NOx emission output. Test vehicle 1, 5 and 7 have no catalytic conversion in the exhaust system, so the small differences between the homologation cycle and the cold start cycle are mainly based on the starting enrichment of the carburetion system

38 Figure 3.3: Comparison of the measured HC+NOx emissions in the homologation cycle and in the cold start test cycle [%] 0 Test vehicle 1 Test vehicle 2 Test vehicle 3 Test vehicle 4 Test vehicle 5 Test vehicle 6 Test vehicle 7 Test vehicle 8 Figure 3.4: Difference of the HC+NOx emissions between the homologation cycle and in the cold start cycle Fuel consumption The fuel consumption (Figure 3.5), measured in the homologation cycle pictures an averaged behavior of each tested vehicle, whereas the consumption during the

39 different conditions (acceleration phase, maximum speed phase, 20 km/h constant speed- and deceleration phases) have not been researched individually. The best fuel consumption of the compared vehicles reaches the vehicle driven by a four stroke engine and carburetor technology (test vehicle 5 and 6). The differences in the fuel consumption of the same vehicles with various exhaust gas after treatment strategies (test vehicle 5 and 6 respectively test vehicle 7 and 8) are less than 5% and can be explained by the tolerance of the measurement procedure. The higher fuel consumption of the supercharged four stroke prototype engine in comparison with the naturally aspirated four stroke engine is based on the significant higher power output during the acceleration phase of test vehicle 7 and [km/l] 10 0 Test vehicle 1 Test vehicle 2 Test vehicle 3 Test vehicle 4 Test vehicle 5 Test vehicle 6 Test vehicle 7 Test vehicle 8 Figure 3.5: Comparison of the average fuel consumption in the homologation cycle With the exception of test vehicle 4 the two stroke engine driven vehicles show higher fuel consumptions than the test vehicles with four stroke engines. The measurement results straggle within 100%: Test vehicle 5 is able to drive about 50 km with one liter fuel in the tank, whereas test vehicle 3 would stop with an empty tank after a 25 km travel according the homologation cycle scheme. Considering, that the emission output of the greenhouse gas CO 2 increases with rising fuel consumption, the four stroke engines and the two stroke concept with direct fuel injection provide a more environment friendly technology

40 RESULTS OF THE RECORDER MEASUREMENT SERIES The time dependent detection of single exhaust gas components enables a detailed study of the drive units regarding their emission behavior. The following diagrams picture the results of the recorder measurements during the complete ECE R47 homologation cycle, whereas the first four cycles belong to the cold start test cycle. The recorder results are approximately for 10 seconds delayed due to the setup of the measuring devices. Beside the treated emission concentrations (C1Hm, CO and NOx), the specified vehicle speed of the homologation cycle and the actual speed of the tested vehicles are shown in the diagrams to point out the influence of the engine load. Exhaust gas after treatment by catalytic conversion in two stroke engine applications: Comparison of test vehicle 1 and 2 To point out the influence of an oxidation catalyst on the emission output of two stroke engines with carburetor visible, Figure 3.6 and Figure 3.7 show a comparison of test vehicle 1 and Test vehicle 2: Two stroke engine with carburetor and oxidations catalyst. Test vehicle 1: Two stroke engine with carburetor 60 v_cycle v_vehicle HC C1Hm [ppm] v_vehicle [km/h] v_cycle [km/h] Time [s] Figure 3.6: Comparison of test vehicle 1 and 2, C1Hm emission concentration 0 0 The concentration of the untreated C1Hm emission is directly influenced by the engine load. The peak values in the acceleration phases are about 250% higher than the mean values of the measured cycles. At idle speed the concentration decreases down to about 30% of the mean value

41 The C1Hm concentration in the exhaust gas of the test vehicle without catalyst (test vehicle 1) decreases about 30% after the cold start enrichment phase during the first cycle within about 100 seconds. After that, the curve progressions in the last six cycles are similar to maximum values of about 2300ppm. The tested vehicle with an oxidation catalyst (test vehicle 2) shows a significantly different characteristic: After the first cycle, where the concentration is nearly the same as at test vehicle 1, the catalytic conversion leads to a large reduction of the HC emissions. The mean value of the measured C1Hm concentration drops down to about 150ppm, pointing to a catalytic oxidation efficiency of more than 80%. The progression of the CO concentration is not as much dependent on the engine load as the progression of the HC. Peak values are visible at full load (acceleration phase) in the same way as during the 20 km/h constant velocity phase. At idle speed the concentration drops down to minor values. In the cold start phase during acceleration extraordinary high peaks of the untreated exhaust gas (more than 3000 ppm) point to the enrichment strategy of the carburetor. After the light off time the catalytic conversion reduces the mean value of the CO concentration down to about 60%. Test vehicle 2: Two stroke engine with carburetor and oxidations catalyst Test vehicle 1: Two stroke engine with carburetor v_cycle v_vehicle CO CO [ppm] v_vehicle [km/h] v_cycle [km/h] Time [s] Figure 3.7: Comparison of test vehicle 1 and 2, CO emission concentration

42 Test vehicle 6: Four stroke engine with carburetor, secondary air system and oxidation catalyst. Test vehicle 5: Four stroke engine with carburetor and secondary air system v_cycle v_vehicle HC C1Hm [1130] C1Hm [ppm] v_vehicle [km/h] v_cycle [km/h] Time [s] Figure 3.8: Comparison of test vehicle 5 and 6, C1Hm emission concentration Exhaust gas after treatment by catalytic conversion in four stroke engine applications: Comparison of test vehicle 5 and 6 A comparison of the time dependent C1Hm concentration in the exhaust gas of test vehicle 5 and 6 in Figure 3.8 explains the influence of a catalytic conversion on the HC emission output. The divergency of the C1Hm concentration in the exhaust gases are based on the different after treatment procedures: Whereas test vehicle 5 is equipped with a secondary air induction, the exhaust system of test vehicle 6 includes an additional oxidation catalyst. After the cold start phase the catalytic converter works with a high efficiency and reduces the HC emissions down to a low mean level of about 60 ppm mean value. The concentration of the C1Hm emissions of the four stroke engine driven scooters is legibly smaller than those from the two stroke engine driven vehicles equipped with carburetor, where especially during the cold start phase the output of HC emissions is significantly higher. This is valid for engines without catalyst (compare test vehicles 1 and 5) in the same way as for engines with catalytic exhaust gas after treatment (compare test vehicles 2 and 6). As well during the warm cycles the two stroke engine without catalyst (test vehicle 1) shows mean value differences of more than 600% compared with the four stroke engine without catalyst (test vehicle 5). This points to the concept based disadvantages of the used two stroke engine. A comparison of the HC emission

43 output of the vehicles with catalytic exhaust gas after treatment (test vehicle 2 and 6) pictures the high conversation efficiency of the oxidation catalyst in case of an optimized two stroke engine application: The HC- mean value difference between the four stroke engine and the two stroke engine, both equipped with an oxidation catalyst, decreases down to about 33%. Figure 3.9 shows the curve progressions of the NOx output of test vehicle 5 and 6. The reduced output of the test vehicle with oxidation catalyst is based on the reduction of NOx under partly rich conditions in the exhaust system. Test vehicle 6: Four stroke engine with carburetor, secondary air system and oxidation catalyst Test vehicle 5: Four stroke engine with carburetor and secondary air system v_cycle v_vehicle NOx NOX [ppm] v_vehicle [km/h] v_cycle [km/h] Time [s] Figure 3.9: Comparison of test vehicle 5 and 6, NOx emission concentration Comparison of the scooter driven by a two stroke engine with air assisted fuel injection system plus oxidation catalyst and the scooter driven by a four stroke engine with fuel injection system plus oxidation catalyst (test vehicles 4 and 8) With the help of electronic fuel injection systems both, test vehicle 4, driven by a two stroke engine, and test vehicle 8, driven by a supercharged four stroke engine, are able to reach low exhaust emission levels and provide powerful performance characteristics at the same time. Test vehicle 4 meets the Euro II homologation target with the help of an oxidation catalyst and shows moderate higher HC emissions and significant higher CO emissions in the cold start cycle, whereas test vehicle 8 reaches very low emission levels in the homologation cycle and also in the cold start cycle. The advantages of the four stroke engine regarding the C1Hm concentration in the exhaust gas are shown in Figure

44 2000 Test vehicle 8: Four stroke engine with FI, secondary air system and oxidation catalyst Test vehicle 4: Two stroke engine with air assisted direct injection and oxidation catalyst. 60 v_cycle v_vehicle HC C1Hm [ppm] v_vehicle [km/h] v_cycle [km/h] Time [s] Figure 3.10: Comparison of test vehicle 4 and 8, C1Hm emission concentration 0 0 The more intensive cold start enrichment of test vehicle 4 on the one side, and the slowed down light-off time of the oxidation catalyst on the other side, lead to a significant increase of the HC output during the first three cycles. [10] The four stroke engine completes its cold start phase very quick after about 70% of the first cycle. This strategy leads to a low C1Hm concentration in the cold start cycle. During the last five ( warm ) cycles the C1Hm concentration mean value of the four stroke engine is about 60% below the mean value of the two stroke engine, explaining the clear difference of the cycle measurement results. The same explanations regarding the cold start strategy of test vehicle 4 stated above are also guilty for the discussion of the CO concentrations pictured in Figure An intense enrichment during the warm up phase in combination with a delayed starting of the catalytic conversion leads to high CO peak levels during the first three cycles. These peaks are responsible for the increased CO value of the cold start test cycle detected in the CVS measurement series. During the last five cycles the air assisted direct injection system is able to play its advantages, lying in the decrease in the CO output, thus enables satisfying results in the homologation cycle. The supercharged four stroke engine shows a remarkable low CO concentration during the whole test cycle. After a short warm up phase of about 100 seconds the CO level drops down to a mean value of about 30 ppm. This low output of CO emissions enables an excellent emission characteristic in the homologation cycle and in the cold start cycle

45 Test vehicle 8: Four stroke engine with FI, secondary air system and oxidation catalyst Test vehicle 4: Two stroke engine with air assisted direct injection and oxidation catalyst v_cycle v_vehicle CO CO [ppm] v_vehicle [km/h] v_cycle [km/h] Time [s] Figure 3.11: Comparison of test vehicle 4 and 8, CO emission concentration CONCLUSION OF THE TRANSIENT TEST CYCLE BASED STUDIES The results of the emission measurement series show the different requirements of the ECE R47 homologation cycle, which does not consider the cold start behavior, and a second test cycle, which also detects the emission output during the cold start. The cold start test cycle, designed to serve as basis for the research work published in this paper, allows a study of the engine behavior during the warm up phase. The emission characteristics during the warm up phase are essential to reach low emission levels in the cold start test cycle. This can be improved with the help of a short starting enrichment phase in combination with a short light off time of the catalyst. Eventually, only engine concepts equipped with catalytic conversion systems will be able to fulfill more severe future exhaust gas emission regulations. For this reason, a short summary evaluates the results of the tested vehicles with catalyst: The test vehicles driven by two stroke engines with carburetor technology in combination with oxidation catalysts show different results. The low cost scooter (test vehicle 2) meets the Euro II homologation target and reaches the third-best HC+NOx emission values of all tested vehicles. The scooter with secondary air induction in combination with a two catalyst system produce increased exhaust emission. But for all that, both tested vehicles show a clear increase of the emissions in the cold start cycle, challenging therefore the qualification for future emission regulations

46 Test vehicle 4, driven by a two stroke engine with air assisted direct fuel injection system and a catalytic conversion in the exhaust system, shows the best power output characteristics of all test series. The emission behavior is characterized by lower levels in the homologation cycle but legible higher values in the cold start cycle. An optimization of the enrichment strategy during the warm up phase of the engine on the one side, and the catalyst light-off time on the other side, is able to qualify this engine concept for future emission regulations. The scooter driven by a four stroke engine with carburetor technology in combination with a secondary air induction and an oxidation catalyst (test vehicle 6) shows high CO emission values, whereas the HC+NOx emission level is quite low. An optimization of this engine concept can lead to a significant lowering of the CO output, whereas the engine responsibility in transient conditions has to be considered to guarantee a satisfying drivability. For future emission regulations, also including cold start cycles, the qualification of this engine concept depends on the limiting CO values. The tested vehicle driven by a supercharged four stroke engine with fuel injection system and exhaust gas after treatment by secondary air induction in combination with an oxidation catalyst (test vehicle 8) shows a remarkable emission characteristic together with a powerful performance output. In both test procedures, cold start as well as homologation cycle, this engine concept reaches the best values of all competitors. Due to the future proof and well tested injection and exhaust gas after treatment technology, this engine concept provides a large potential for future emission regulations. The choice of appropriate technologies able to fulfill future exhaust emission regulations, can only be made when knowing the future test cycles and limiting values. Based on the results published in this paper, giving an overview of the state of the art technologies in the 50cc two wheeler motor vehicle class and not claiming completeness, the following assessment can be stated: Two stroke engines with carburetor technology as used today will have problems to meet the future regulations which include cold start, if the limiting values and the test cycle are similar to the existing ECE R47 homologation cycle. Two stroke engines with direct injection systems are able to fulfill the requirements of future emission regulations based on cold start, because of the possibility to prevent fuel scavenge losses. Four stroke engines with carburetor technology are able to meet future regulations due to the fine cold start behavior, but only if the CO values are moderately limited and the lean engine setting enables a satisfying drivability of the vehicles. Four stroke engines with fuel injection technology will have no problems to fulfill future emission regulations including cold start. Electronic fuel injection is standard in automotive applications, whereas the resulting technologic and economic synergetic effects support an implementation into small capacity engine classes. Catalytic converters in two stroke engines have to be placed carefully in the exhaust system to keep the influence on the gas dynamic effects to a minimum. As known from car engines the catalyst can be placed near to the

47 cylinder head to shorten the light-off time and thus to additionally improve the cold start behavior in four stroke engine applications. Considering that further steps of exhaust emission regulations within the next years will lead to a further lowering of the permitted emission levels, four stroke engines with closed loop controlled fuel injection systems in combination with three way catalytic systems seem to be a future proof technology for a wide field of application

48 4. EXHAUST EMISSION REDUCTION IN SMALL CAPACITY TWO- AND FOUR-STROKE ENGINE TECHNOLOGIES FOR STATIONARY EMISSION REGULATIONS 4.1 RESEARCHED ENGINE TECHNOLOGIES This chapter contains the analysis and the evaluation of comparable two- and fourstroke engine concepts with a displacement of 50 cm 3, including a selection of mixture preparation systems, like carburetor, indirect and direct fuel injection systems. In addition, the suitability of different exhaust gas after treatment concepts, namely secondary air induction, newly developed oxidation catalysts and three way catalytic converters is evaluated and assessed for each engine technology. The exhaust emission characteristics of the applied technologies are discussed in terms of the present emission regulations in the focused engine classes. 4 STROKE ENGINES Two different technologies will be introduced as representatives of the 4 stroke engine category. The first engine, engine A-4S (Table 4.), is a mass production liquid cooled 4 stroke engine. It represents a low cost engine concept in the 4 stroke engine class. The liquid cooling system guarantees a high power output under different ambient conditions and enables an easy handling in a large number of applications. Beside the liquid cooled 50 cm 3 4 stroke engine concepts, a number of air cooled engines are on the market. The air cooling technology lowers the production costs, but shows some disadvantages regarding the performance and the emission behavior. Mixture preparation of the first representative engine is performed by an 18 mm diameter constant pressure carburetor. Maximum engine power of 3.1 kw is reached at rated speed of 9000 rpm and lambda 1.0. This engine is designed as a long stroke engine with 2 valves and OHC with a compression ratio of 12:1. To enable a satisfying cold start characteristic, a thermo switch choke comes to use. Engine A-4S: Liquid cooled 4 stroke carburetor engine Carburetion system Constant pressure carburetor, 18 mm diameter Power [kw] 3.1 BMEP [bar] 8.3 Rated speed [rpm] 9000 Displacement [cm 3 ] 49.9 Bore x Stroke [mm x mm] 38 x 44 Valve train 2 valves, OHC, chain Compression ratio 12 : 1 Cold start system Thermo switch choke Cooling system Liquid Table 4.1: Engine A-4S - liquid cooled 4 stroke carburetor engine

49 As a possible high performance 4 stroke engine technology with a modern mixture preparation system, a supercharged engine with intake manifold fuel injection is presented. The engine B-4S (Table 4.1) is a pre-serial prototype engine, which uses the bottom side of the piston for supercharging the intake air. This engine concept reaches a maximum power output of 4.1 kw under rich combustion at 9000 rpm. The compression ratio in the combustion chamber is 10:1; the pre-compression ratio of the supercharging system is about 1.5:1. The valve train drives 2 valves with OHC. The cooling pump is driven by the crankshaft. Cold start is controlled by the ECU application. Engine B-4S: Liquid cooled 4 stroke supercharged fuel injected engine Carburetion system Intake manifold fuel injection Power [kw] 3.7 at lambda at lambda 0.9 BMEP [bar] 9.9 at lambda at lambda 0.9 Rated speed [rpm] 9000 Displacement [cm 3 ] 49.2 Bore x Stroke [mm x mm] 40 x 39.2 Valve train 2 valves, OHC, chain Compression ratio 10 : 1 Cold start system ECU application Cooling system Liquid Table 4.1: Engine B-4S - liquid cooled 4 stroke supercharged fuel injected engine 2 STROKE ENGINES The benefits of 2 stroke engines, like low production costs, light weight and high performance density make this engine technology attractive for a big number of applications. Two 2 stroke engine concepts will be discussed in this paper. The first 2 stroke concept, engine C-2S (Table 4.2), represents an air cooled lean burn carburetor mass production engine. The maximum power output of 1.9 kw at 4500 rpm is reached at a slightly lean operation point. The crank train is designed as a long stroke crank train. The engine is cooled with driven air. A hand choke supports the cold start behavior. Engine C-2S: Air cooled 2 stroke carburetor engine Carburetion system Slide carburetor with 14 mm diameter Power [kw] 1.9 BMEP [bar] 5.7 Rated speed [rpm] 4500 Displacement [cm 3 ] 49.9 Bore x Stroke [mm x mm] 38 x 44 Compression ratio 7 : 1 Cold start system Hand choke Cooling system Air cooling Table 4.2: Engine C-2S - air cooled 2 stroke carburetor engine

50 The highly sophisticated 2 stroke engine category is represented by the forth engine concept (engine D-2S, Table 4.3). It is a pre-series prototype engine with a low cost direct fuel injection system. With stoichiometric mixture conditions, a maximum power output of 3.1 kw at 6500 rpm can be reached. This engine is liquid cooled and the cold start characteristic is controlled by the ECU application. Engine D-2S: Liquid cooled 2 stroke direct fuel injected engine Carburetion system direct fuel injection Power [kw] 3.1 BMEP [bar] 5.8 Rated speed [rpm] 6500 Displacement [cm 3 ] 49.3 Bore x Stroke [mm x mm] 40 x 39.2 Compression ratio 11.7 : 1 Cold start system ECU application Cooling system Liquid cooled Table 4.3: Engine D-2S - liquid cooled 2 stroke direct fuel injected engine Production costs and weight A cost and weight comparison of the different engine concepts is included in Figure 4.1. For comparison, the air cooled two stroke engine with carburetor (C-2S) has been used as the baseline. The production effort of the high technology two stroke engine with liquid cooling and fuel injection system (D-2S) rises the costs about 40% above the standard engine, whereas the weight surplus amounts just about 15%. Both four stroke engine concepts show clearly higher production costs and moderately increased engine weight. The more complex build up of four stroke engines (primarily the valve train and the lubrication system) leads to a significant increase of the production costs at slightly increased engine masses. 200 Production costs Engine weight Relative value [%] A-4S B-4S C-2S D-2S Figure 4.1: Comparison of production costs and engine weight

51 4.2 EXHAUST EMISSIONS The discussion of untreated exhaust emissions is based on the measured hydrocarbons, oxides of nitrogen and the carbon monoxide exhaust emissions output. The four engines could be compared under several test cycles like for mopeds, handheld or non-handheld test cycles. To give the best possible overview of the specific exhaust emissions and applied exhaust emission technologies of handheld engine technologies the test cycle ISO G3 (Table 4) was chosen. Mode number 1 2 Engine Speed Rated speed Idle speed Load [%] Weighting factor Table 4: ISO G3 This test cycle consists of one power mode at rated speed and one idle mode. The weighting factors are 85 percent for the wide open throttle mode and 15 percent for the idle mode. The results are presented in g/kwh. MEASUREMENT RESULTS OF UNTREATED EXHAUST EMISSIONS All treated engines were analyzed on the engine test bench regarding their power output and the specific exhaust emission characteristics. Especially fundamental studies of untreated exhaust emissions, as there are the influence of a rich or a lean combustion on the exhaust emissions and performance of Engine B-4S, could be researched. Results of the CO, HC and NOx behavior [g/kwh] in the test cycle G3 are shown in Figure 4.2. At rich combustion, high CO values, higher HC and lower NOx values occur. The slightly increased NOx output at lean combustion can be explained with a higher combustion temperature. The sum of HC+NOx is comparable. Rich and Lean Combustion - Emissions 4 stroke supercharged fuel injected engine G3 Cycle Exhaust Emissions [g/kwh] CO HC NOx HC+NOx Figure 4.2: Engine B-4S emissions of rich and lean combustion Lambda 0.9 Lambda

52 In comparison with a rich mixture setting, a stoichiometric mixture preparation leads to a loss of power output of approximately 10 % (Figure 4.3), but to a reduction of the untreated CO emission output of more than 95 % in the test cycle G3. Rich and Lean Combustion - Power 4 stroke supercharged fuel injected engine Power [kw] Engine speed [rpm] Lambda 0.9 Lambda 1.0 erfser Engine speed at Lambda 0.9 Engine speed at Lambda 1.0 Figure 4.3: Engine B-4S power of rich and lean combustion Evaluation of the emission characteristics with the ISO G3 cycle The tested engine concepts are compared based on the measurements in the G3 test cycle. The evaluation allows a comparison of the different engine concepts, whereas similar lambda values have been adjusted. Lambda 1.0 was adjusted at WOT operation, therefore all engines shows similar CO values for raw exhaust emission output, except for the engine C-2S where lean combustion with a lambda value about 1.2 was realized. At part load different air fuel mixture settings were realized, so different CO values for all engines can be observed (Figure 4.4). In addition, the influence of lambda 1.0 combustion on engine B-4S was tested. The performance improvement and therefore higher CO emissions can be seen in Figure 4.4. Both 4 stroke engines show extraordinary low HC output in the untreated exhaust emissions, which is based on smaller scavenge losses during the load exchange section. It is remarkable, that the supercharged engine with the largest power output of all presented engines shows very low HC+NOx emission values. The benefits of the engine with the highest hydrocarbon output (the 2 stroke carburetor engine) go along with a good compactness at the lowest production costs of all compared engines

53 CO [g/kwh] Engine technologies evaluated under ISO G3 cycle 20; 332 A-4S B-4S B-4S lambda 1.0 C-2S D-2S 84; ; 27 20; ; HC + NOx [g/kwh] Figure 4.4: Evaluation of presented engine technologies with ISO G3 test cycle 4.3 EMISSION REGULATION Present and future emission regulations are the driving force for R&D all over the world. Presented engines could be used for several applications, as there are driving units for mopeds or lawn mowers, stationary engines, etc. The engine and drive train design needs an adaptation of each application, but the fundamental technologies are based on the same structure. The OFF-ROAD exhaust emission regulations in the USA, the special regulations in California and the European legislation serve as a basis for the emission related assessment of the treated engine categories. All three legislations rest on the same test cycle (Table 4) and on similar engine classifications. A difference is drawn in the emission component limits for handheld and non-handheld application. The USA regulation and the California regulation define the same test cycle (ISO G3) for handheld and non-handheld engines for the treated engine classes (handheld 20-50cm 3, non-handheld <66 cm 3 ). In Europe a test cycle (ISO G2) with several weighting factors at rated speed is used for non-handheld application. For a better comparison of the emission values, the same test cycle (ISO G3) was applied in the present publication. European Union Classification of engines and emission limits are divided into two main categories, depending on the kind of equipment to be used, either handheld or non-handheld application. This split complies with the natural spreading between the segment

54 totally dominated by 4 stroke engines and the one in which 2 stroke engines are frequent. For valid limits Stage 1 from August 2004 is used. The limits for this stage are listed in Table 4.5. Class Stage 1 August 2004 CO HC NOx HC + NOx g / kwh PM Displacement cm 3 g / g / g / kwh kwh kwh Handheld Nonhandheld < g / kwh Stage 2 August Handheld Nonhandheld with deterioration factor < Table 4.5: Engine classification and emission limits in Europe For future EU regulation Stage 2 will be used from August 2007 onward. The HC and NOx emissions are combined for handheld engines. The limits for HC+NOx are also lowered. For the non-handheld application a deterioration factor is implemented. An additional limitation for the NOx emission of 10 g/kwh for all engine classes is presented. PM emissions are not restricted. USA - EPA In the United States regulations have the same limits as in Europe, as presented in Stage 2 ( Table 4.6 and Figure 4.5). No additional NOx limits are specified. PM emission components are not limited. Class Stage 1 August 2005 cm 3 CO HC NOx g / kwh g / kwh g / kwh HC + NOx g / kwh PM g / kwh Displacement Handheld Class IV Nonhandheld Class 1-A < Table 4.6: Engine classification and emission limits in USA EPA California - CARB

55 CARB regulates all engines below 19 kw maximum power output, not depending on the kind of application. In comparison with the USA EPA and the European regulation, the CO values are reduced, whereas the HC+NOx limits remain on the same level. Extra limitation of particulate emissions for two stroke engines is considered. A voluntary engine class is presented as a Blue Sky Engine Class with 50% lowered HC+NOx emissions. A limitation of PM is given. Class Stage 1 August 2005 Displacement CO HC NOx HC + NOx g / kwh PM (1) cm 3 g / g / g / g / kwh kwh kwh kwh - < Blue Sky Series - voluntary exhaust emissions < (1) Applicable to all two-stroke engines Table 4.7: Engine classification and emission limits in California The valid emission limit for non-handheld equipment (Figure 4.5) presented in Europe is slightly lower than the CARB limit. CARB presents the lowest CO limit of all presented regulations. The same HC+NOx emission maximum value for all presented regulations can be observed. Voluntary limits, which include a 50% reduction of the HC+NOx output at the same CO value, are specified in the CARB regulation. Future CO limits for EU (August 2007) are increased to the same HC+NOx maximum value, due to the implemented deterioration factor. Off-road Emission Limits EU, EPA, CARB Handheld < 50cc CO [g/kwh] EU August 2007= EPA August 2005 EU August 2004 CARB August 2005 CARB Blue Sky August HC+NOx [g/kwh] Figure 4.5: Exhaust emission limits for European, American and Californian legislation for non-handheld engines

56 EU regulation for handheld engines (Figure 4.6) presents relatively high HC and NOx limits. In this regulation the HC and NOx limits are presented separately. The future legislation joins these two emission factors to one limited value. More severe values, similar to EPA and CARB regulations, will be presented in August EPA and EU show the same CO maximum values with the most challenging CO limit in CARB. Similar to the non-handheld regulations, a voluntary blue sky regulation is defined in California. Off-road Emission Limits EU, EPA, CARB Non-handheld < 66cc CO [g/kwh] EU August 2007 with DF = EPA August 2005 CARB August 2005 EU August 2004 CARB Blue Sky August HC+NOx [g/kwh] Figure 4.6: Exhaust emission limits for European, American and Californian legislation for handheld engines The discussed regulations, applied on treated engines, are explained in Figure 4.7. It can be stated, that all engines without exhaust gas after treatment fulfill the valid EU regulation limits. The most challenging limits, presented in the CARB emission regulation, are shown as dotted line. Two stroke engines with oxidation catalyst can reach these limits easily. It is noticeable, that the 4 stroke engines, even engine B-4S with rich combustion, can reach the most demanding regulation without exhaust gas after treatment. All engine technologies with the use of exhaust gas after treatment are presenting lower emission values as voluntarily defined limits

57 CO [g/kwh] Engine technologies evaluated under ISO G3 cycle HC + NOx [g/kwh] A-4S A-4S KAT B-4S lambda 0.9 B-4S lambda 0.9 KAT B-4S lambda 1.0 B-4S lambda 1.0 KAT C-2S C-2S KAT D-2S D-2S KAT Figure 4.7: Application of regulations for evaluated engine technologies CARB 4.4 EXHAUST EMISSIONS AFTERTREATMENT TECHNOLOGIES Due to the high production cost pressure, small engine technologies are limited to low cost exhaust gas after treatment technologies with high efficiency and high reliability. Available technologies are catalytic oxidation and secondary air induction for 4 and 2 stroke engine applications. The three way catalyst technology can only be used at 4 stroke engines due to the problematic application of a lambda sensor in 2 stroke engines. Catalysts The first initial development on catalytic converters started in the early 1960 s. In the last years efforts were made to use metal as a substrate for the catalysts in small capacity engine applications. The benefits of using metal instead of ceramic substrates are not only the increased catalytic efficiency due to higher substrate surface at the same dimensions, but also increased transfer of the gas phase to the channel walls. For a further increase of the catalytic conversion, specific structures can be introduced in the metal substrate in the channel walls. In this way a laminar flow after intrusion in the catalytic converter can be observed. After a short time a laminar flow of the standard catalyst can be changed into a turbulent flow behavior. Longer residence time and more unconverted gases from the core of the channel come closer to the catalyst surfaces and more reaction takes place. More efficient and cost effective converters, such as turbulent TS and LS structure catalytic converters [11] can be presented in this way

58 In Transversal Foil Structure (TS) the corrugated foils are embossed with secondary micro- corrugations (Figure 4.8), which are provided transverse to the direction of flow i.e. 90 degree to the flow direction. Figure 4.8: TS structure design with flow details In Longitudinal Structure (LS) catalyst the corrugated foil is characterized by additional cuts and depressions to provide shovel like shapes (Figure 4.9). Figure 4.9: LS structure design with flow details These counter corrugations, oriented into the basic channels, create the effect of additional channels within the same given volume, which results in a turbulent mass transfer to the channel walls and in an increased catalytic reaction. Stationary and dynamic tests (presented as an example for one tested operation point in Figure 4.10) on the test bench show that a 15 % smaller catalyst with turbulent structure offers the same or even better conversion efficiency compared to the reference catalyst with 100 % volume. Detailed results of test bench tests can be seen in [11]