Measurement of Heat and Mechanical Losses in Internal Combustion engines

Transcription

1 Sudan University of science and technology COLLEGE OF ENGINEERING School of mechanical engineering DEPARTMENT OF POWER A Project Submitted In Partial Fulfillment for the Requirement of the Degree of B.Sc. (Honor) In Mechanical Engineering Measurement of Heat and Mechanical Losses in Internal Combustion engines Prepared by: 1. Fayad Idris Ahmed Mohammed. 2. Mohammed Taj Elser Ali Abdallah. 3. M men Hassan Abdelrahman Taha. Supervised by: Eltayeb Hassan Elshaikh (September 2015)

2 قال تعالى : -I-

3 DEDICATION We dedicate this research to all our friends and families, our great teachers, and brothers in 27 mech. -II-

4 انح د هلل أوال و أخ سا صاحب انشكس و انعسفا انعز ز ان ا وانصالة وانسالو عهى يعهى انبشس ت و صاحب انخهق انسف ع عه ه و عهى آل ب ته و أصحابه أتى انصالة و انتسه ى انشكس يىصىل نألستاذ \ انط ب حس انش خ انري كا نه د انفضم بعد اهلل عز وجم بتىج هه وزعا ته نهرا انبحث وانشكس يىصىل أ ضا ن دزست انه دست ان كا ك ت ي ثهت ف أساترتها انكساو و ألساترة وزشت انس ازاث بقسى انقدزة وكم ي ساهى ف إخساج هرا انبحث -III-

5 ABSTRACT This thesis focuses on measurement of the heat and mechanical losses in I.C.engines based on a gasoline engine data operated on different engine speeds. The objective is to determine the classic and modern methods of measurement the heat and mechanical losses. The transfer of energy is measured for losses to the engine coolant and exhaust, usable power output, as well as friction losses. A major part of the energy is lost with the exhaust gases. In addition, another major part of energy input is rejected in the form of heat via the cooling system. Energy loss increases with increasing engines speed and load and thus the mechanical efficiency decreases. Future improvements to obtain distinguishable results are outlined. -IV-

6 انتجس دة تزكش ذ األطز حت عهى قباص انفق داث انحزار ت ان كا ك ت ف يحزكاث اإلحتزاق انداخه. ان دف ي ذ األطز حت دراست األسان ب انطزق انقد ت انحد ثت نق اص انفق داث انحزار ت ان كا ك ت ف يحزكاث اإلحتزاق انداخه. ن حزك د شل تى ق اص انفق داث بسبب انتبز د غاساث انعادو انقدرة انفزيه ت ان ستفادة انقدرة اإلحتكاك ت. جشء كب ز ي انطاقت تى فقدا ف غاساث انعادو باإلضافت إنى جشء كب ز أ ضا ب اسطت ي اة انتبز د. انفق داث انحزار ت ان كا ك ت تش د بش ادة انسزعت اند را ت نه حزك ي ا ؤدي إنى قصا انكفاءة ان كا ك ت. ال بد ي تحس اث ف ان ستقبم نهحص ل عه تائج أفضم. -V-

7 LIST OF CONTENTS Content Page اال ت I DEDICATION II شكز عزفا III ABSTRACT IV انتجز دة V LIST OF CONTENTS VI LIST OF FIGURES VIII LIST OF TABLES IX CHAPTER ONE INTRODUCTION 1.1 Research Importance Research Problem Research Objective Research Methodology 3 CHAPTER TWO LITERATURE REVIEW 2.1 Introduction Internal combustion engines Engine performance Calorific value of fuels Performance Parameters 9 Previous studies 15 CHAPTER THREE METHODS OF MEASUREMENT OF HEAT AND MECHANICAL LOSSES 3.1 Measurement of Heat Losses Heat Balance Sheet Measurement of mechanical losses Measurement of brake power 27 -VI-

8 3.2.2 Important types of dynamometers 28 Content Page Methods of measurement of mechanical losses The Willan s line method The Morse test Motoring test Difference between I.P. and B.P Engine Test cells Overall size of individual test cells General purpose automotive engine test cells Research and development engine and 48 Power-train test cells Automotive engine production test cells 50 (hot test) Cold testing in production Engine handling systems 52 CHAPTER FOUR PRACTICAL TRAILS 4.1 Morse test Engine heat balance sheet 61 CHAPTER FIVE CONCLUSION AND RECOMMENDATION 5.1 Conclusion Recommendations 67 References 68 -VII-

9 LIST OF FIGURES Figure Title page 2.1 Internal Combustion Engine Indicator diagram Heat balance diagram Prony brake dynamometer Rope brake dynamometer Hydraulic dynamometer Eddy current dynamometer Transmission dynamometer Willan s line for a diesel engine Test cell General Purpose test cell Engine test cells with shared control rooms Engine speed related with friction power 60 -VIII-

10 LIST OF TABLES Table Title Page 2.1 Heat balance sheet Approximate percentage values of losses Some actual cell dimensions found in UK industry Morse test data recorded Heat balance data recorded Heat balance sheet 64 -IX-

11 CHAPTER ONE

12 INTRODUCTION When it comes to Internal Combustion Engines and all types of engines we as engineers our target is to reach for the maximum efficiency of the engine, to achieve that we need to reduce losses in the engine, but we need firstly to recognize and determine these losses, then define the methods and devices which used to measure these losses in order to reduce them eventually. These losses reduce the engine power by a large rate and waste a lot of energy which can be used, so by reducing these losses we will increase the efficiency of the engine. In this research we will study the losses in internal combustion engines and the methods to measure them. In order to do that firstly we will collect data from some references, search for previous researches, and finally we will do some specific practical trails and tests to calculate the amount of the losses. 1.1 Research Importance: Measuring heat and mechanical losses in internal combustion engine to be able to be reduced in order to contribute to the development of engine performance and access the highest possible efficiency. -2-

13 1.2 Research Problems: The main problem of this research is the thermal and mechanical losses in the I.C. engine which reduce the engine efficiency. 1.3 Research Objectives: The main objective of this research is to measure the heat and mechanical losses in the I.C engine by determining: 1- Mechanical Losses (friction power). 2- Engine Heat Balance Sheet. 1.4 Research Methodology: Data Collection: in our research we used scientific data that we had collected from different references such as (internal combustion engines by R.K Rajput, internal combustion engines by V Ganesan, engine testing by A.J Martyr, M.A Plint) Practical trails: in our research we will do some specific practical trails and tests to calculate the amount of the losses (indicated power by Morse method, Heat balance sheet) -3-

14 CHAPTER TWO

15 LITERATURE REVIEW 2.1 Introduction: Generally we define heat engines as any type of engine or machine which derives heat energy from the combustion of fuel or any other source and convert this energy into mechanical work. Heat engines may be classified into two main classes as follow: I. External combustion engines. II. Internal combustion engines. 2.2 Internal combustion engines: In this case, combustion of fuel with oxygen of air occurs within the cylinder of the engine. The internal combustion engines group includes engines employing mixtures of combustible gases and air, known as gas engines, those using lighter liquid fuel or spirit known as petrol engines and those using heavier liquid fuels known as oil compression ignition or diesel engines. -5-

16 Fig (2-1): Internal combustion engine -6-

17 2.3 Engine performance: One ultimate measure of the performance of an internal combustion engine is the proportion of the heat of combustion of the fuel that is turned into useful work at the engine coupling. The thermal efficiency at full load of internal combustion engines ranges from about 20 per cent for small gasoline engines up to more than 50 per cent for large slow-running diesel engines, which are the most efficient means currently available of turning the heat of combustion of fuel into mechanical power. It is useful to have some idea of the theoretical maximum thermal efficiency that is possible, as this sets a target for the engine developer. Theoretical thermodynamics allows us, within certain limitations, to predict this maximum value. The proportion of the heat of combustion that is not converted into useful work appears elsewhere: in the exhaust gases, in the cooling medium and as convection and radiation from the hot surfaces of the engine. In addition, there may be appreciable losses in the form of unburned or late burning fuel. It is important to be able to evaluate these various losses. Of particular interest are losses from the hot gas in the cylinder to the containing surfaces, since these directly affect the indicated power of the engine. The so-called adiabatic engine seeks to minimize these particular losses. -7-

18 2.4 Calorific value of fuels: The calorific value of a fuel is defined in terms of the amount of heat liberated when a fuel is burned completely in a calorimeter. Since all hydrocarbon fuels produce water as a product of combustion, part of these products (the exhaust gas in the case of an I.C.Engine) consists of steam. If, as is the case in a calorimeter, the products of combustion are cooled to ambient temperature, this steam condenses, and in doing so gives up its latent heat. The corresponding measure of heat liberated is known as the higher or gross calorific value (also known as gross specific energy). If no account is taken of this latent heat we have the lower or net calorific value (also known as net specific energy). Since there is no possibility of an internal combustion engine making use of the latent heat, it is the invariable practice to define performance in terms of the lower calorific value. -8-

19 2.5 Performance Parameters: The basic performance parameters of internal combustion engine (I.C.E) may be summarized as follows: Indicated power (I.P.): It is the actual rate of work done by the working fluid on the piston. As its name implies, the I.P. can be determined from an "indicator diagram" as show in figure (1), by subtracting the pumping loop area (- ve) from the positive area of the main diagram. I.P. power could be estimated by performing a Morse test on the engine. The physical equation for the I.P. is: I.P = PmLAN Where N is the number of machine cycles per unit times, which is 1/2 the rotational speed for a four- stroke engine, and the rotational speed for a two- stroke engine. -9-

20 Fig (2-2): Indicator diagram, four-stroke engine Brake power (B.P.): This is the measured output of the engine. It is usually obtained by a power absorption device such as a brake or dynamometer which can be loaded in such a way that the torque exerted by the engine can be measured. The break power is given by: B.P = 2πNT Where T is the torque. -10-

21 2.5.3 Friction power (F.P.) and Mechanical efficiency (η m ): The difference between the I.P. and the B.P. is the friction power (F.P) and is that power required to overcome the frictional resistance of the engine parts, F.P. = I.P. B.P. The mechanical efficiency of the engine is defined as: η m = η m is usually between 80% and 90% Indicated mean effective pressure (IMEP): It is a hypothetical pressure which if acting on the engine piston during the working stroke would results in the indicated work of the engine. This means it is the height of a rectangle having the same length and area as the cycle plotted on a p- v diagram. IMEP (P i ) = Indicator scale Consider one engine cylinder: Work done per cycle = Pi AL Where: A = area of piston; L = length of stroke -11-

22 Work done per min. = work done per cycle active cycles per min. I.P. = Pi AL active cycles/ min To obtain the total power of the engine this should be multiplied by the number of cylinder n, i.e.: And Total I.P. = PiALNn/2 ) four- stroke engine ( = PiALNn ) Two- stroke engine ( Brake mean effective pressure (BMEP) and brake thermal efficiency: The BMEP (B.P) may be thought of as that mean effective pressure acting on the pistons which would give the measured B.P., i.e. B.P. = Pb AL active cycles/ min The overall efficiency of the engine is given by the brake thermal efficiency: η BT = Where m f is the mass of fuel consumed per unit time, and Qnet is the lower calorific value of the fuel. -12-

23 2.5.6 Specific fuel consumption (S.F.C): It is the mass of fuel consumed per unit power output per hour, and is a criterion of economic power production. Low values of S.F.C. are obviously desired. Typical best values of B.S.F.C. for SI engines are about 270g/kw.h, and for C.I. engines are about 200g/kw.h Indicated thermal efficiency (η IT ): It is defined in a similar way to η BT Dividing ηbt by ηit gives -13-

24 2.5.8 Volumetric efficiency (η v ): Volumetric efficiency is only used with four- stroke cycle engines. It is defined as the ratio of the volume if air induced, measured at the free air conditions, to the swept volume of the cylinder: The air volume may be refereed to N.T.P. to give a standard comparison. The volumetric efficiency of an engine is affected by many variables such as compression ratio, valve timing, induction and port design, mixture strength, latent heat of evaporation of the fuel, heating of the induced charge, cylinder pressure, and the atmospheric conditions. -14-

25 2.6 Previous Studies: Here are some examples of previous studies in Measurement of Heat and Mechanical Losses in I.C.Engines: First Study: Title: MEASUREMENT OF MECHANICAL LOSSES IN THE COMBUSTION ENGINES By: Andre Drab, Stanislav Beroun, Robert Vozenilek (Technical University of Liberec, Department of Vehicles and Engines /2011) As the basis of the testing station for measuring mechanical losses in piston combustion engine by induced revolution there serves a regulating induction motor of the firm SIEI, type MA 133 K-62, with the output 28 kw/6000 1/min. The torque during induced revolution is measured by a shaft pick-up HBM of the type T20WN (100 Nm, 0.2%, /min), or by a pick-up HBM T5 (50 Nm, 0.1%, /min) both pick-ups can be overloaded statically to 200% of nominal value of Mt. Because of the required range of r. p.m., the basic configuration of the testing rig is equipped with the pick-up T20WN. -15-

26 Measurement system: The testing rig for induced revolution of the engine is coupled with a data logger MGC plus (Hottinger), allowing to record samples of data per second in the 8-channel version of the amplifier. Each sample comprehends the data from the pick-up of the torque (Mt and revolutions) and from 13 temperature pick-ups (Pt 100 and thermocouples). The number of sensed temperatures can be increased according to measuring needs. From the effective values of the measured torque and r. p.m., the power loss is calculated. The operational environment for measuring passive resistances is generated by means of the SW CAM-tan Easy. During measuring, on the PC monitor there are displayed graphical values of measured temperatures and the time courses of Mt and n. The values of all measured quantities (Mt, n and temperatures) for each measured regime are established by statistic data processing (as mean values of the data file in chosen time interval). Results of measurement: For the comparison of courses of the torque loss, two temperature regimes have been chosen as the first temperature regime, 35 C have been chosen for both media (lubrication oil and coolant/water) for cold engine, and as the second one, 90 C for both media (lubrication oil and coolant/water) for warm engine. The combustion engine has been resolved in the range of r. p.m. The step of a change of r. p.m. has been chosen to amount to 250 r. p.m. The value at the highest measured velocity r. p.m. is considered in the diagrams as 100 %, and other values of -16-

27 measured torque loss have been related to this value. The diagrams allow noticing the tendency of the measured torque loss to increase with increasing r. p.m. of the revolved combustion engine. With a cold combustion engine, the measured torque loss for the highest measured r. p.m. (5.500 r. p.m.) is 1.82 time higher than at the lowest measured velocity (1.500 r. p.m.). With a warmed-up combustion engine (warm engine 90o C), the difference of the measured torque loss between r. p.m. and r. p.m. increases to as much as 2.13 multiple. Conclusion: The verifying measuring of mechanical losses of a piston combustion engine by means of induced revolution on the testing rig have proved full functionality of the testing rig, both concerning the requirement to measure the torque loss with high precision and repeatability, and maintaining stable temperature conditions during measuring by means of regulation of temperatures of coolant and lubrication oil. The results of measuring carried out until now show that by means of the testing station for measuring mechanical losses in piston combustion engines by induced revolution it is also possible to study such characteristics of the engine that other (calculation or experimental) procedures do not show. -17-

28 2.6.2 Second Study: Title: ENERGY LOSSES IN A VEHICLE Only about 15 percent of the energy from the fuel you put in your tank gets used to move your car down the road or run useful accessories, such as air conditioning. The rest of the energy is lost to engine and driveline inefficiencies and idling. Therefore, the potential to improve fuel efficiency with advanced technologies is enormous. Engine Losses percent In gasoline-powered vehicles, over 62 percent of the fuel's energy is lost in the internal combustion engine (ICE). ICE engines are very inefficient at converting the fuel's chemical energy to mechanical energy, losing energy to engine friction, pumping air into and out of the engine, and wasted heat. Advanced engine technologies such as variable valve timing and lift, turbo charging, direct fuel injection, and cylinder deactivation can be used to reduce these losses. In addition, diesels are about percent more efficient than gasoline engines, and new advances in diesel technologies and fuels are making these vehicles more attractive. Idling Losses percent In urban driving, significant energy is lost to idling at stop lights or in traffic. Technologies such as integrated starter/generator systems help reduce these -18-

29 losses by automatically turning the engine off when the vehicle comes to a stop and restarting it instantaneously when the accelerator is pressed. Accessories percent Air conditioning, power steering, windshield wipers, and other accessories use energy generated from the engine. Fuel economy improvements of up to 1 percent may be achievable with more efficient alternator systems and power steering pumps. Driveline Losses percent Energy is lost in the transmission and other parts of the driveline. Technologies, such as automated manual transmission and continuously variable transmission, are being developed to reduce these losses. Aerodynamic Drag percent A vehicle must expend energy to move air out of the way as it goes down the road less energy at lower speeds and progressively more as speed increases. Drag is directly related to the vehicle's shape. Smoother vehicle shapes have already reduced drag significantly, but further reductions of percent are possible. Rolling Resistance percent Rolling resistance is a measure of the force necessary to move the tire forward and is directly proportional to the weight of the load supported by the tire. A variety of new technologies can be used to reduce rolling resistance, -19-

30 including improved tire tread and shoulder designs and materials used in the tire belt and traction surfaces. For passenger cars, a 5-7 percent reduction in rolling resistance increases fuel efficiency by 1 percent. However, these improvements must be balanced against traction, durability, and noise. Overcoming Inertia; Braking Losses percent To move forward, a vehicle's drive train must provide enough energy to overcome the vehicle's inertia, which is directly related to its weight. The less a vehicle weights, the less energy it takes to move it. Weight can be reduced by using lightweight materials and lighter-weight technologies (e.g., automated manual transmissions weigh less than conventional automatics). In addition, any time you use your brakes, energy initially used to overcome inertia is lost. Source: Comment: This study about ENERGY LOSSES in vehicles as general, because it deals with all energy losses in vehicle at all, but our research is about heat and mechanical losses in internal combustion engine only which mean energy losses inside the engine. -20-

31 2.6.3 Third Study: Title: Mechanical Losses in an Engine Science Daily (Jan. 12, 2012) No less than one third of a car's fuel consumption is spent in overcoming friction. This friction loss has a direct impact on both fuel consumption and emissions. New technology can reduce friction by anything from 10% to 80% in various components of a car, according to a joint study by VTT Technical Research Centre of Finland and Argonne National Laboratory (ANL) in USA. It should thus be possible to reduce car's fuel consumption and emissions by 18% within the next 5 to 10 years and up to 61% within 15 to 25 years. Source: (University of IITDELHI) P M V Subarea Professor Mechanical Engineering Department -21-

32 CHAPTER THREE

33 METHODS OF MEASUREMENT OF HEAT AND MECHANICAL LOSSES 3.1 Measurement of Heat Losses: The thermal performance of an engine is usually studied by heat balance-sheet Heat Balance Sheet: The main components of the heat balance are: Heat equivalent to the effective (brake) work of the engine, Heat rejected to the cooling medium, Heat carried away from the engine with the exhaust gases, and Unaccounted losses. The unaccounted losses include the radiation losses from the various parts of the engine and heat lost due to incomplete combustion. The friction loss is not shown as a separate item to the heat balance-sheet as the friction loss ultimately reappears as heat in cooling water, exhaust and radiation. To draw heat balance sheet for I.C.E, it is run at constant load. Indicator diagram is obtained with the help of indicator. The quantity of fuel used in a given time and its calorific value, the amount, inlet and outlet temperature of cooling water and the weight of exhaust gases are recorded. After calculating I.P. and B.P. the heat in different items is found as follows: -23-

34 (i) Heat supplied by fuel: Heat supplied = m f C.V. Where: m f mass of fuel used per minute (kg) C.V. lower calorific value of fuel (kj) (ii) Heat absorbed in I.P: Heat equivalent of I.P. (per minute) = I.P. 60 kj (iii) Heat taken away by cooling water: Heat taken away by cooling water = m w c w (t 2 t 1 ) Where: m w = Mass of cooling water used per minute. c w = Specific heat of water. t 1 = Initial temperature of cooling water t 2 = Final temperature of cooling water. (iv) Heat taken away by exhaust gases: Heat taken away by exhaust gases = m e c pg (te -t r ) Where: m e = Mass of exhaust gases per minute (kg/min) Cpg = Specific heat of exhaust gases -24-

35 t e = Exhaust gases temperature t r = Room temperature * Mass of exhaust gases can be obtained by adding the mass of fuel supplied with the mass of air supplied. Item kj/min Per cent Heat supplied by fuel (i) (ii) (iii) (iv) Heat absorbed in I.P Heat taken away by cooling... water Heat taken away by exhaust... gases Unaccounted losses Total Table (2-1) Heat balance sheet table -25-

36 Fig (3-1): Heat balance diagram The following table gives the approximate percentage values of various losses in SI and CI engines: Engine % B.P. % Heat cooling water % Heat to exhaust gases % unaccounted losses S.I C.I Table (2-2): approximate percentage values of losses -26-

37 3.2 Measurement of mechanical losses: It is a curious fact that, in the long run, all the power developed by all the road vehicle engines in the world is dissipated as friction: either mechanical friction in the engine and transmission, rolling resistance between vehicle and road or wind resistance. Mechanical efficiency, a measure of friction losses in the engine, is thus an important topic in engine development and therefore engine testing. It may exceed 80 per cent at high power outputs, but is generally lower and is of course zero when the engine is idling. To measure friction loss we have to measure both of indicated and brake power Measurement of brake power: Brake power is the power output of the engine or the power developed in crankshaft. To measure brake power we need to measure the torque and angular speed of the engine. The device which we use to measure the torque is called Dynamometer, the Dynamometer is always be loaded then we can measure the generated torque -27-

38 3.2.2 Important types of dynamometers: A- Absorption Dynamometers : These dynamometers measure and absorb the power output of the engine to which they are coupled. The power absorbed is usually dissipated as heat by some means. Example of such dynamometers is Prony brake rope brake, hydraulic dynamometer, etc. 1- Prony brake: This type is consist of frame with brake shoes, often made of two blocks of wood, each of which embraces slightly less than one-half of the rotating drum rim. The drum is attached to the output shaft of the engine. The two blocks can be drawn together by means of nuts and bolts, cushioned by springs, so as to increase the pressure on the drum. A load bar extends from the top of the brake and a weight is hanged to the end of the load bar. -28-

39 Fig (3-2): Prony brake dynamometer W = weight Torque = w r Brake power = This type of dynamometer must be cooled since the power absorbed is converted into heat. This way is not suitable for absorption of large amount of power as wear of blocks and reduction in the coefficient of friction between drum and the friction material with the rise in temperature require continues tightening of the bolts -29-

40 2- Rope Brake : This type is directly coupled to the engine output shaft. In this brake two or more ropes rest on the rim of pulley. The ropes are spaced evenly across the width of the rim by means of wooden blocks positioned at different points around the rim. The total pull on the slack end of the ropes is registered on a spring balance, while the pull on the tight end is provided by dead weights. The power absorbed is due to friction between rope and the drum.friction torque on the pulley maybe increased by increasing the dead load by addition of weights. Brake Power = W = dead weight S = spring balance N = engine speed r.p.m R = effective radius of pulley -30-

41 Fig (3-3): Rope brake dynamometer This dynamometer is easy to fabricate but is not very accurate because of changes in friction coefficient of the rope with temperature. -31-

42 3- Hydraulic Dynamometer: This type of dynamometer works on the principle of dissipating the power in fluid friction rather than in dry friction. In principle its construction is similar to that of a fluid flywheel. It consists of an inner rotating member or impeller coupled to the output shaft of the engine. This impeller rotates in a casing filled with fluid. This outer casing, due to the centrifugal force developed, tends to revolve with the impeller, but is resisted by a torque arm supporting the balance weight. The frictional forces between the impeller and the fluid are measured By the spring-balance fitted on the casing. The heat developed due to dissipation of power is carried away by a continuous supply of the working fluid, usually water. The output can be controlled by regulating the sluice gates which can Be moved in and out to partially or wholly obstruct the flow of water between impeller, and the casing. -32-

43 Fig (3-4): Hydraulic Dynamometer 4- Eddy Current Dynamometer: It consists of a stator on which are fitted a number of electromagnets and a rotor disc made of copper or steel and coupled to the output shaft of the engine. When the rotor rotates eddy currents are produced in the stator due to magnetic flux set up by the passage of field current in the electromagnets. These eddy currents are dissipated in producing heat so that this type of dynamometer also requires some cooling arrangement. The torque is measured exactly as in other types -33-

44 of absorption dynamometers, i.e. with the help of a moment arm. The load is controlled by regulating the current in the electromagnets. Fig (3-5): Eddy Current Dynamometer B- Transmission Dynamometers: Transmission dynamometers, also called torque meters, mostly consist of a set of strain-gauges fixed on the rotating shaft and the torque is measured by the angular deformation of the shaft which is indicated as strain of the strain gauge. Usually, a four arm bridge is used to reduce the effect of temperature to minimum and the gauges are -34-

45 arranged in pairs such that the effect of axial or transverse load on the strain gauges is avoided. Transmission dynamometers are very accurate and are used where continuous transmission of load is necessary. These are used mainly in automatic units. Fig (3-6): Transmission dynamometer -35-

46 3.2.3 Methods of Measurement of Mechanical Losses: The friction force power of an engine is determined by the following methods: (a)willan s line method. (b) Morse test. (c) Motoring test. (d) Difference between Indicated power and Brake power The Willan s line method: This is applicable only to un-throttled compression ignition engines. It is a matter of observation that a curve of fuel consumption rate against torque or B.M.E.P. at constant speed plots quite accurately as a straight line up to about 75 per cent of full power, This suggests that for the straight line part of the characteristic, equal increments of fuel produce equal increments of power combustion efficiency is constant. At zero power output from the engine, all the fuel burned is expended in over-coming the mechanical losses in the engine, and it is a reasonable inference that an extrapolation of the Willan s line to zero fuel consumption gives a measure of the friction losses in the engine. Strictly speaking, the method only allows an estimate to be made of mechanical losses under noload conditions. When developing power the losses in the engine will undoubtedly be greater. -36-

47 Fig (3-7): Willan s line for a diesel engine -37-

48 The Morse test In this test, the engine is run under steady conditions and ignition or injection is cut off in each cylinder in turn: it is of course only applicable to multi-cylinder engines. On cutting out a cylinder, the dynamometer is rapidly adjusted to restore the engine speed and the reduction in power measured. This is assumed to be equal to the indicated power contributed by the non-firing cylinder. The process is repeated for all cylinders and the sum of the reductions in power is taken to be a measure of the indicated power of the engine. A modification of the Morse test makes use of electronically controlled unit injectors, allowing the cylinders to be disabled in different ways and at different frequencies, thus keeping temperatures and operating conditions as near normal as possible Motoring Test: In the motoring test, the engine is first run up to the desired speed by its own power and allowed to remain at the given speed and load conditions for some time so that oil, water, and engine component temperatures reach stable conditions. The power of the engine during this period is absorbed by a swinging field type electric dynamometer, which is most suitable for this test. -38-

49 The fuel supply is then cut-off and by suitable electric-switching devices the dynamometer is converted to run as a motor to drive for motor the engine at the same speed at which it was previously running. The power supply to the motor is measured which is a measure of the F.H.P of the engine. During the motoring test the water supply is also cut-off so that the actual operating temperatures are maintained. This method, though determines the F.P. at temperature conditions very near to the actual operating temperatures at the test speed and load, does, not give the true losses occurring under firing conditions due to the following reasons. (a) The temperatures in the motored engine are different from those in a firing engine because even if water circulation is stopped the incoming air cools the cylinder. This reduces the lubricating oil temperature and increases friction increasing the oil viscosity. This problem is much more severing in air-cooled engines. (b) The pressure on the bearings and piston rings is lower than the firing pressure. Load on main and connecting road bearings are lower. (c) The clearance between piston and cylinder wall is more (due to cooling). This reduces the piston friction. (d) The air is drawn at a temperature less than when the engine is firing because it does not get heat from the cylinder (rather loses heat to the cylinder). This makes the expansion line to be lower than the compression line on the P-v diagram. This loss is however counted in the indicator diagram. -39-

50 (e) During exhaust the back pressure is more because under motoring conditions sufficient pressure difference is not available to impart gases the kinetic energy is necessary to expel them from exhaust. Motoring method, however, gives reasonably good results and is very suitable for finding the losses due to various engine components. This insight into the losses caused by various components and other parameters is obtained by progressive stripping-off of the under progressive dismantling conditions keeping water and oil circulation intact. Then the cylinder head can be removed to evaluate, by difference, the compression loss. In this manner piston ring, piston etc. can be removed and evaluated for their effect on overall friction Difference between I.P and B.P.: (a) The method of finding the F.P by computing the difference between I.P, as obtained from an indicator diagram, and B.P., as obtained by a dynamometer, is the ideal method. However, due to difficulties. (b) In obtaining accurate indicator diagrams, especially at high engine speeds, this method is usually only used in research laboratories. Its use at commercial level is very limited. -40-

51 Comments on Methods of Measuring F.P.: The Willan s line method and Morse tests are very cheap and easy to conduct. However, both these tests give only an overall idea of the losses whereas motoring test gives a very good insight into the various causes of losses and is a much more powerful tool. As far as accuracy is concerned the I.P B.P method is the most accurate if carefully done. Motoring method usually gives a higher value for F.H.P as compared to that given by the Willian s line method. The four standard methods of estimating mechanical losses in an engine and its auxiliaries have been briefly described. No great accuracy can be claimed for any of these methods and it is instructive to apply as many of them as possible and compare the results. Measurement of mechanical losses in an engine is still something of an art. -41-

52 3.3 Engine Test Cells: An engine test cell is a facility used to develop, characterize and test engines. The facility, often offered as a product to automotive, allows engine operation in different operating regimes and offers measurement of several physical variables associated with the engine operation. Engine test cell houses has several sensors (or transducers), data acquisition features and actuators to control the engine state. The sensors would measure several physical variables of interest which typically include: *Crank shaft torque and angular velocity *Intake air and fuel consumption rates, often detected using volumetric and/or gravimetric measurement methods *air-fuel ratio for the intake mixture, often detected using an exhaust gas oxygen sensor *environment pollutant concentrations in the exhaust gas such as carbon monoxide, different configurations of hydrocarbons and nitrogen oxides, sulfur dioxide, and particulate matter *temperatures and gas pressures at several locations on the engine body such as engine oil temperature, spark plug temperature, exhaust gas temperature, intake manifold pressure *atmospheric conditions such as temperature, pressure, and humidity Information gathered through the sensors is often processed and logged through data acquisition systems. Actuators allow for attaining a desired engine state (often characterized as a unique combination of engine torque and -42-

53 speed). For gasoline engines, the actuators may include an intake throttle actuator, a loading device for the engine such as an induction motor. The engine test cells are often custom-packaged considering requirements of the OEM customer. They often include microcontroller-based feedback control systems with following features: *closed-loop desired speed operation (useful towards characterization of steady-state or transient engine performance) *closed-loop desired torque operation (useful towards emulation of in-vehicle, on-road scenarios, thereby enabling an alternate way of characterization of steady-state or transient engine performance) Fig (3-8): Test cell -43-

54 3.3.1 Overall size of individual test cells: One of the early considerations in planning a new test facility will be the space required. The areas to be separately considered are The engine or power train test cell; The control room; The space required for services and support equipment; The support workshop or engine rig and derig area; The storage area required for engine rig items and consumables. A cramped cell, in which there is not room to move around in comfort, is a permanent source of danger and inconvenience. The smaller the volume of the cell the more difficult it is to control the ventilation system under conditions of varying load.as a rule of thumb, there should be an unobstructed walkway 1 meter wide all round the test engine. Cell height is determined by a number of factors including the provision or not of a crane beam in the structure. In practice, most modern automotive cells are between 4 and 4.5 meters internal height. -44-

55 Table (3-1): Some actual cell dimensions found in UK industry: QA test cell for small automotive diesels fitted with eddy-current dynamometer ECU development cell rated for 250kW engines, containing work bench and some emission equipment Gasoline engine development cell with A.C. dynamometer, special coolant and Inter-cooling conditioning Engine and gearbox development bed with two dynamometers in Tee configuration. Control room runs along 9.0 meter wall 6.5m long 4m wide 4m high 7.8m long 6m wide 4.5m high 6.7m long 6.4m wide 4.7m High 9.0m wide 6m 4.2m high (to suspended ceiling) It is often necessary, when testing vehicle engines, to accommodate the exhaust system as used on the vehicle, and this may call for space and extra length in the cell. It must be remembered that much of the plant in the cell requires calibration from time to time and there must be adequate access for the calibration engineer, his instruments and in some cases ladder. The major layout problem may be caused by the calibration of the dynamometer, involving accommodation of a torque arm and dead weights. -45-

56 3.3.2 General purpose automotive engine test cells: follow: This figure represents general purpose automotive engine test cells as Fig (3-9): General Purpose test cell arranged against an outside wall with control desk side on to engine -46-

57 Fig (3-10): Engine test cells with shared control rooms running down the length of the cell Such cells are often built in multiples, side-by-side and in a line with a common control room that is shared by two cells on either side. Engines enter the cell by way of a large door in the rear wall while the operator may enter by way of a door in the front wall to one side of the control desk. Typically there is a double-skinned toughened glass window in front of the control desk. Most wall-mounted instrumentation, smoke meters, fuel consumption meters, etc., is carried on the side wall remote from the cell access door. In cells rated at above about 150kW where engine changes and rigging were carried out in the cell it was usual to provide a crane rail located above -47-

58 the test bed axis with a hoist of sufficient capacity to handle engines and dynamometer. The penalty of such a lifting beam is that the structure has to be built to take the full rated crane load plus its plant support load. In modern cells where the engine is rigged outside the cell and trolley or pallet mounted, in-cell cranes are not usually included as the cost benefit of a crane structure may be judged as marginal Research and development engine and power-train test cells: The term power-train testing is used to cover engine plus direct mounted transmission, but does not cover vehicle transmissions complete with vehicle shafting; these are considered as transmission test rigs. Power-train rigs are often designed to be able to take up different configurations, on a large bedplate, as required by the unit under test (UUT). The typical configurations catered for are: Transverse engine plus gearbox driving two dynamometers; In-line engine and gearbox driving one dynamometer; In-line engine plus gearbox driving two dynamometers ( Tee set-up). To allow fast transition times, the various UUT have to be pallet mounted in a system that presents a common height and alignment to the cell interface points. Automotive engine test and development facilities built since the mid- 1990s will have the following features, additional to those found in general purpose cells: -48-

59 1. Exhaust gas analysis equipment. 2. Dedicated combustion air treatment plant. 3. Ability to run in vehicle exhausts systems. 4. High dynamic four-quadrant dynamometers. Such requirements increase both the volume of the cell and of the space required to house plant such as combustion air treatment equipment and the electrical drive cabinets associated with the A.C. dynamometers. The positioning and condition in which such service plant operates is as important and as demanding as those of the contents of the test cell. While plant such as the A.C. drive cabinets are usually positioned outside the cell, for reasons of ambient temperature and noise, they need to be as close to the dynamometer as practical to avoid higher than necessary costs for the connecting power cable. Modern dynamometer drive cabinets tend to be large, heavy and difficult to maneuver within restricted building spaces. Therefore, expert planning is required, as is anti-condensation heating if there is a long period between installation and commissioning. Combustion air units also need to be close to the engine to prevent heat loss or gain through the delivery trucking. They are often positioned in the service room immediately above the engine, with the delivery duct running via a fire damper through the cell ceiling to a flexible duct attached to the engine as part of the rigging process. If the humidity of the combustion air is being controlled, the unit will require condensation and steam drains out of the building or into foul water drains. -49-

60 Typical applications are: Development departments of vehicle and engine manufacturers and major oil companies; Motor-sport developers; Specialist consultancy companies; Government testing and monitoring laboratories Automotive engine production test cells (hot test): These cells are highly specialized installations forming part of an automation system lying outside the scope of this research. The objective is to check, in the minimum possible process time, that the engine is complete and runs. Typical floor-to-floor times for small automotive engines range between 5 and 8 minutes. The whole procedure engine handling, rigging, clamping, filling, starting, draining and the actual test sequence is highly automated, with interventions, if any, by the operator limited to dealing with fault identification. Leak detection may be difficult in the confines of a hot test stand therefore it is often carried out at a special (black-light) station following test. The test cell is designed to read from identity codes on the engine and recognize variants to adjust the pass or fail criteria accordingly. Typical measurements made during a production test include: Time taken for engine to start. -50-

61 Cranking torque. Time taken for oil pressure to reach normal level. Exhaust gas composition. Most gasoline engines are no longer loaded by any form of dynamometer during a hot test, but in the case with diesel engines load is applied with power output measured and recorded Cold testing in production: In addition to rotational testing in processes of subassemblies, cold testing is sometimes applied to (near) completely built engines. This is a highly automated process. Cold test rigs are invariably situated within the assembly process line fed by a power and free or similar conveyor system. The mechanical layout, based on docking on to a drive motor and transducer pick-up system, is physically simpler than a hot test cell since it does not require fuel supplies or hot gas and fluid evacuation. Cold test areas also have the cost advantage of being without any significant enclosure other than safety guarding Engine handling systems: A considerable number of connections must be made to any engine before testing can proceed. These include the coupling shaft, fuel, cooling water, exhaust and a wide range of transducers and instrumentation. It is -51-

62 obviously cost-effective when dealing with high throughput of small automotive units to carry out such work in a properly equipped workshop rather than use expensive test cell space. Once rigged the engines have to be transported to the cell. The degree of complexity of the system adopted for transporting, installing and removing the engine within the cell naturally depends on the frequency with which the engine is changed. In some research or lubricant test cells the engine is more or less a permanent fixture, but at the other extreme the test duration for each engine in a production cell will be measured in minutes, and the time taken to change engines must be cut to an absolute minimum. There is a corresponding variation in the handling systems: Simple arrangements when engine changes are comparatively infrequent. The engine is either craned into the cell and rigged in situ or mounted on a suitable stand such as that shown in Fig. 4.4 which is then lifted, by crane or forklift, into the cell. All connections are made subsequently by skilled staff with workshop back-up. The pre-rigged engine is mounted on a wheeled trolley or truck maneuvered pallet carrying various transducers and service connections which are coupled to the engine before it is moved into the cell. An engine rigging workshop needs to be fitted with a dummy test cell station that presents datum connection points identical in position and detail to those in the cells, particularly the dynamometer shaft in order for the engine to be pre-aligned. Clearly to gain maximum benefit, each cell in the facility needs to be built with critical fixed interface items in identical positions from a common -52-

63 datum. These positions should be repeated by dummy interface points in any pre-rigging stand, in the workshop. For production test beds it is usual to make all engines to pallet connections prior to the combined assembly entering the cell. An automatic docking system permits all connections (including in some cases the driving shaft) to be made in seconds and the engine to be filled with liquids. Workshop support in the provision of suitable fittings and adaptors should always be made available. All pipe connections should be flexible and exhaust connections can be particularly troublesome and short-lived at high temperatures; they should be treated as consumable items. Rigging of exhaust systems often requires a welding bay; this must obey regulations concerning shielding. Electrical arc welding must not be allowed within the test cell because of the danger of damage to instrumentation by stray currents. The workshop area used for derigging should be designed to deal with the inevitable spilled fluids and engine wash activities. Floor drains should run into an oil intercept unit. -53-

64 CHAPTER FOUR

65 PRACTICAL TRAILS In this chapter we will discuss the practical trails that we have done and show the results of these tests. 4.1 Morse test: Tools: 1-Diesel Engine: (4stroke engine, 4cylender) 2-Dynamometer: (Hydraulic Dynamometer/ H-P-A TEST) 3-Water Pump: (0.5HP) 4-Water Tank Theory: Brake Power = I 1 = B.P B 1 Where: B 1 = B.P. when cylinder 1 is cut off. -55-

66 I 1 = I.P. of cylinder 1 I 2 = B.P. B 2 I 3 = B.P. B 3 I 4 = B.P. B 4 I T = I 1 + I 2 + I 3 + I 4 F.P = I.P B.P Ƞ mech = Methodology: We ran the engine at stable speed 1000 r.p.m., then we applied load and the result torque was recorded, then we cut off the first cylinder, the torque was measured by keeping the speed constant, then the same for the other cylinders, and for different speeds. Table(4-1): Data Recorded: N (r.p.m.) T BP T 1 T 2 T 3 T 4 (N.m)

67 Calculations: 1- At 1000 r.p.m: B.P. = = = 7.86 kw B 1 = = = 5.57 kw B 2 = = = 5.61 kw B 3 = = = 5.59 kw B 4 = = = 5.58 kw I 1 = B.P. B 1 = 2.29 kw I 2 = B.P. B 2 = 2.25 kw I 3 = B.P. B 3 = 2.27 kw I 4 = B.P. B 4 = 2.28 kw I T = I 1 + I 2 + I 3 + I 4 = 9.09 kw F.P. = I.P. B.P. = = 1.23 kw -57-

68 Ƞ mech = = = % 2- at 2000 r.p.m: B.P. = = = kw B 1 = = = 13.3 kw B 2 = = = kw B 3 = = = kw B 4 = = = kw I 1 = B.P. B 1 = 5.72 kw I 2 = B.P. B 2 = 5.68 kw I 3 = B.P. B 3 = 5.76 kw -58-

69 I 4 = B.P. B 4 = 5.68 kw I T = I 1 + I 2 + I 3 + I 4 = kw F.P. = I.P. B.P. = = 3.82 kw Ƞ mech = = = % 3- at 3000 rpm: B.P. = = = kw B 1 = = = kw B 2 = = = kw B 3 = = = kw B 4 = = = kw I 1 = B.P. B 1 = 9.11 kw I 2 = B.P. B 2 = 9.89 kw -59-