HEAVY DUTY SI NG ENGINES

Transcription

1 HEAVY DUTY SI NG ENGINES Assessing the Future Market and Choosing The Right Technology Johannes Andersen AVL MTC AB

2 HEAVY DUTY SI NG ENGINES CONTENTS 1. Introduction 2. Market trends 3. A few words on Infrastructure 4. Drivers 5. NG Engine Technologies 6. Combined analysis 7. Conclusions Johannes Andersen AVL MTC 19 november

3 INTRODUCTION Factors that affect how to approach the design of NG engines! What technology is inherited?! Volumes! Applications (current and future)! Infrastructure (hen and the egg)! Fuel quality Johannes Andersen AVL MTC 19 november

4 INTRODUCTION Factors that affect how to approach the design of NG engines! What technology is inherited?! Volumes! Applications (current and future)! Infrastructure (hen and the egg)! Fuel quality Johannes Andersen AVL MTC 19 november

5 MARKET ANALYSIS - SETTING THE SCENE Johannes Andersen AVL MTC 19 november

6 MARKET TRENDS, FORECAST EU 7,5k 45k vehicles HD/Light trucks Russia 4,1k 75k vehicles Light/HD trucks and Heavy buses China 90k 350k vehicles HD/Light trucks and buses US 27k 150k vehicles HD/MD/Light trucks Japan 2,5k 3,5k vehicles Light trucks, Heavy bus and MD Trucks South America 5,1k 25k vehicles Light/HD trucks and Heavy buses India 16,5k 35k vehicles Heavy bus, Light trucks and Genset Asia/Pacific 54k 175k vehicles Light trucks totally dominating Light truck: 3,5-6 t MD truck: 6-16 t HD truck: 16 t+ Heavy bus: 8 t+ Johannes Andersen AVL MTC 19 november

7 MARKET TRENDS, FORECAST Summary:! Current vehicle fleet is approximately HD NGVs*! Expected to increase to approximately HD NG vehicles by 2028! About 2/3 of all HD NG vehicles will be found in Asia and China! The rest basically in US and EU! 8-10 liter engines will dominate in Asia and China! liter (and bigger) engines will dominate in EU and US! Asia and EU markets will be policy driven! US market will be cost driven *) OEM figures, excluding retrofit and similar conversions Johannes Andersen AVL MTC 19 november

8 A FEW WORDS ON INFRASTRUCTURE! EU: TEN-T Network, 9 transport corridors! Blue Corridor project, 7 LNG corridors! LNG4HUAL, Pre-study in the Netherlands! Greening road transport, Case study! US: Natural gas highway, 5 main corridors, Clean Energy and Shell tank stations, Chesapeake a large supplier! China: LNG corridors, although still to some extent local, beginning to take form Johannes Andersen AVL MTC 19 november

9 MORE ON THE BASIC DRIVERS [$/gal DGE] Source: U.S. EIA / Annual Energy Outlook 2010 Source: Large NG importers: Asia and EU! Large NG exporters: Africa and Middle East! Neutral/self sufficient: US and South America Johannes Andersen AVL MTC 19 november

10 NG ENGINE TECHNOLOGIES - BASICS AND TEASERS Johannes Andersen AVL MTC 19 november

11 COMBUSTION SYSTEM, GENERAL DIESEL& GAS " Swirl based " Flat head " Less heat rejection into head & coolant OTTO & GAS " Tumble based " Roof type head " High heat rejection into head & coolant The basic system layout requirements:! Homogeneous mixture preparation! Enough turbulence at location of ignition for flame-kernel growth! High turbulence for fast flame front propagation! Short distances for the flame to reach high burn rate! No cavities where end-gas is stored that leads to knocking or HC emissions! Good cooling to reduce temperature (knocking) Johannes Andersen AVL MTC 19 november

12 COMBUSTION SYSTEM, DIRECT INJECTION! Increase volumetric efficiency by reducing charge displacement (injection after intake closing)! Enables scavenging strategies without methane slip! Promotes charge motion and turbulence depending on injection strategy! Supply pressure ~20bar require a additional pump for LNG operation! Nozzle tip temperature issues during engine braking have not been investigated for HD application Cylinder Spark plug location Hom. early Turbulence distribution Hom. late Stratified Early inj. λ=1 Late inj. λ=1 Late inj. stratified λ=2.6 Johannes Andersen AVL MTC 19 november

13 ENGINE BREATHING! Basically load from the SI engine is controlled by throttling, which in turn leads to pumping losses! This means that the camshaft has an even more critical role, that may be simplified by variability! Reduced pumping losses by early inlet valve closing and valve overlap! Knock suppression by Miller cam timing! Better low end torque by scavenging strategies! Conventional valve timing leads to the highest volumetric efficiencies and can realize the highest EGR rates under the assumed boundary conditions, but leads to pumping losses! Miller timing achieves advantages regarding fuel consumption and exhaust gas temperature despite its volumetric efficiency handicaps due to its low knock tendency, however will set very tough requirements for the transient behavior of the charging system Johannes Andersen AVL MTC 19 november

14 BASE ENGINE LAYOUT CONSIDERATIONS Not recommended! Tandem valve pattern has poor TMF behavior for a bank head design, because all valve bridges are in line and therefore handicapped at expansion! Slightly skewed and skewed valve pattern is common approach on diesel engines due to swirling combustion system! Very skewed valve pattern has no advantage but very complex valve train Recommended for SI! Parallel valve pattern has some specific advantages:! More suitable if tumble is desired! Typically better flow capacity! Shorter port lengths! Should however be realized only in combination with a DOHC concept Johannes Andersen AVL MTC 19 november

15 COOLING! Total cooling demand as approximately 10-15% higher on an EGR cooled CNG engine compared to a diesel equivalent! EGR cooler requirement is proportionally higher for the CNG engine, about 50% more cooling power required AVL TOP DOWN COOLING WITH SPARK PLUG SLEEVE Assembled injector sleeve: Coolant direction from the upper water jacket to the lower water jacket Johannes Andersen AVL MTC 19 november

16 ANALYSIS - SIMPLIFIED APPROACH Johannes Andersen AVL MTC 19 november

17 COMBINED ANALYSIS Enablers:! Infrastructure! Policy! $ Outsource/Retrofit! High carry-over! Lower quality Relative volume Asia Buses General trend based on market analysis Organic growth! Tech/volume proportional! High quality Trucks EU/US Diesel carry-over Technology Refined NG Technology South America Maintaining share! High carry-over! Lower quality Strategic effort! High refinement! Improved quality Construction Agricultural Future trends OEM Approach Applications Markets Johannes Andersen AVL MTC 19 november

18 DEEPER STUDY Relative volume Policy $ Buses Appropriate Tech:! CVVT! CNG DI! Advanced Charging Concepts Transient performance Infrastructure $ Long Haulage Trucks CO2 legislation Full load performance Appropriate Tech:! 2 step VVL / Miller timing! Combustion system refinement! Friction! LNG Refined NG Technology Johannes Andersen AVL MTC 19 november

19 CONCLUSIONS! We are going to see an increase of HD NG vehicles in the upcoming years! There are many fundamental differences between a SI engine and a CI engine! It is not a question of how to design the best NG SI engine that is the issue, but rather how to foresee the moving boundaries and to accurately balance them! There are several approaches viable for each OEM, and the technology route is depending on! What s the current engine portfolio! Expected volumes! Which applications are targeted, and on which markets! Infrastructure! Fuel quality - How to balance these factors is key when determining NG engine design strategy! Johannes Andersen AVL MTC 19 november

20 THANK YOU

21 BACKUP Johannes Andersen AVL MTC 19 november

22 MARKET DRIVERS AND TRENDS Drivers and Limiting Factors Drivers Limiting Factors Fuel Economy High Diesel price in Europe & US Cost of CNG/LNG filling station, refill time Infrastructure GHG / CO2 Forthcoming GHG legislation Europe, US, Japan Dual fuel systems not allowed under current emissions legislation test cycles Regulations Corporate Sustainability Corporate Green Image increasing focus on NG, alternative fuels and hybridization vs. Multiple SI system options; DF systems only retrofit; HPDI not implemented so far Technology Options Energy Security Substitution of imported oil with natural gas; utilization of locally produced shale gas, coal bed methane and bio-gas Significant first cost; inconsistent incentives Cost Urban Emissions Lower noise levels CNG/LNG tank requirement balance between packaging, payload and range Range Johannes Andersen AVL MTC 19 november

23 FUTURE DEDICATED HD NG ENGINE Base engine concept! 6 Cylinder Inline Block:! GCI250 Liner type:! wet liner! Top stop S/B:! 1.15 S/B Long stroke Valve Train! DOHC! Miller Cycle*! VVT or Cam Phaser* EGR System! HP + LP System Charging System! 1 St! twin scroll Control! no in cylinder feedback Fuel System:! Mid Pressure DI + MPFI EAS! CC Primary TWC! Secondary TWC Ignition System! Conventional Spark plug M14 WHR*! T-Compound! ORC-WHR Cylinder head! Flat top! Port Arrangement Port Arrangement! Slightly Skewed or. parallel *) just for premium product w/o for budget engine Johannes Andersen AVL MTC 19 november

24 COMBUSTION SYSTEM, GENERAL The basic system layout requirements:! Homogeneous mixture preparation! Low velocity, enough turbulence at location of ignition for flame-kernel growth! High turbulence for fast flame front propagation! Short distances for the flame to reach high burn rate! No cavities where end-gas is stored that leads to knocking or pre-ignition! Good cooling to reduce temperature (knocking) Conventional approach! Advanced combustion timing! Turbulence generation by squish flow and swirl! Reentrant type piston bowl! Lower level of exhaust gas temperature High efficiency approach! Retarded combustion timing! Turbulence generation by tumble motion! Open type bath tub combustion bowl! Allows for higher compression ratio! Higher exhaust gas temperatures! Lower PFP SI combustion system allows for higher engine speeds and higher specific power if frictional losses and transmission boundaries can be sacrificed Johannes Andersen AVL MTC 19 november

25 BASE ENGINE LAYOUT CONSIDERATIONS DIESEL& GAS " Swirl based " Flat head " Less heat rejection into head & coolant OTTO & GAS " Tumble based " Roof type head " High heat rejection into head & coolant Johannes Andersen AVL MTC 19 november

26 COMBUSTION SYSTEM, PISTON DESIGN Variant sphere state of art bowl Flame propagation State of art disc Johannes Andersen AVL MTC 19 november

27 MORE GENERAL TECHNICAL ITEMS! Lean burn engines typically achieve about 18bar BMEP! Stoichiomentric gas engines of up to 21bar BMEP are commercially available! Dual fuel can achieve higher specific loads than SI engines, however have a limited gas substitution rate! HPDI potentially allows for same BMEP as parent diesel engine! SI engine concepts in order of efficiency:! Lean burn with SCR! Stoich with EGR EURO VI viable! Lean burn with MOC only Johannes Andersen AVL MTC 19 november

28 COMBUSTION SYSTEM, TYPE OF TURBULENCE! High Tumble charge motion - High tumble is an efficient way to generate enough charge motion for mixture preparation and turbulence Johannes Andersen AVL MTC 19 november

29 GAS ENGINE TECHNOLOGIES MAIN TECHNOLOGY ROUTES AVAILABLE FOR HD GAS ENGINES SI Lean burn SI Stoichiometric Dual fuel High Pressure DI! Cost effective solution for NOx legislations >2g/kWh! Power density limited by knock / misfire and emissions! Similar thermal loads as Diesel! w/o aftertreatment for NOx above 2g/kWh! Need Oxi-Cat and SCR for EU6, US14,T4! High ignition system demands! Require high charging system capabilities! Main route for EU6, US EPA14, T4! Cost effective solution Three- Way Catalyst! Improved trans. torque vs. lean burn concept! High thermal loads! Cooled EGR optionally to reduce thermal load & knock sensitivity! Known OBD strategies! Improved trans. torque vs. lean burn concept! Efficiency and power density limited by knock! Knock sensitivity w. low methane no. fuels! Reliable technology with limited emission potential! Full load on Diesel possible! Premixed combustion - Diesel micro pilot or Diesel combustion with gas substitution! Similar thermal loads as Diesel! Limited substitution potential! Challenging in view of emission compliance (CH4)! Need highly efficient MOC +SCR +DPF +Thermal management for EU6, US14,T4! Complex technology with high efficiency potential! Limp home on Diesel possible! Diffusion combustion on gas - Diesel micro pilot! Efficiency and power density similar to Diesel! Similar thermal loads as Diesel! Need Oxi-cat and SCR +DPF +Thermal management for EU6,US14,T4! Maturity of technology for On-road HD Johannes Andersen AVL MTC 19 november

30 WHAT ARE THE DRIVERS FOR THE EFFICIENCY DIFFERENCE BETWEEN DIESEL AND GASOLINE? Diesel engines have: Lean combustion High compression ratio Stratification TC EGR The effects are: Dilution High expansion ratio Wall heat loss reduction?? Torque NOx reduction Gasoline engines today have: Lambda=1 combustion Moderate compression ratio Homogeneous mixture NA or TC Three way catalyst Effects needed: Combustion with dilution High expansion ratio Homogeneous mixture for RDE NA for response, TC for torque Conversion of all gaseous emissions Technology: Cooled EGR Miller or articulated crank Lambda=1 TC + E-SC for torque Three way catalyst Natural gas engines look to combine benefits of gasoline and diesel what is the optimum specification? Johannes Andersen AVL MTC 19 november

31 TECHNOLGY TRANSFER BETWEEN DIESEL AND GASOLINE ENGINES DIESEL ENGINE GASOLINE ENGINE Direct Injection Turbocharging Lean NO x Aftertreatment Auto Ignition Variable valve train Catalyst heating strategies External cooled EGR Stoichiometric operation Elect. heated cat Particulate Filter Int. exh. manifold Var. compr. ratio Johannes Andersen AVL MTC 19 november

32 TECHNOLGY TRANSFER BETWEEN DIESEL AND GASOLINE ENGINES DIESEL ENGINE GASOLINE ENGINE Direct Injection Turbocharging Lean NO x Aftertreatment Auto Ignition Variable valve train Catalyst heating strategies External cooled EGR Stoichiometric operation Elect. heated cat Particulate Filter Int. exh. manifold Var. compr. ratio Johannes Andersen AVL MTC 19 november

33 CURRENT BSFC SITUATION (EQUAL BMEP) Full load min. BSFC ~ 230 g/kwh BMEP - bar GASOLINE 240 Δ ~30 g/kwh (Δ 13%) min. BSFC ~ 200 g/kwh DIESEL Engine Speed - rpm Sweet Spot BSFC < 240 g/kwh BMEP - bar 240 Engine Speed - rpm Johannes Andersen AVL MTC 19 november

34 OPTIMUM BOWL-TYPE COMBUSTION CHAMBER DESIGN BY FLAME PROPAGATION BIONIC DESIGN 1. Optimization of the piston bowl shape for fast flame front combustion speed. Main target: modify the combustion bowl in a way that the flame front is not hindered by piston top land surfaces # The flame front should hit the piston crown surface very late and, ideally, simultaneously. # The piston bowl shape is defined by the flame front 1 Bowl contour step x+1 Bowl contour step x Optimization of the dead volume in the lateral gap 3. Optimization of the squish gap area around piston bowl The volume of the lateral gap should be small to have the maximum possible volume available for the combustionoptimized piston shape. Optimization Small gaps hinder the propagation of the flame front. This leads to a retarded combustion speed for late combustion phases. Similar to the lateral gap, the volume of the squish gap should be small. This leads to a strong squish effect of this area. Optimization Squish areas can hinder the flame front propagation if the timing of the reversesquish effect does not fit to the position of the flame front. Johannes Andersen AVL MTC 19 november

35 CRANK TRAIN FOR HD & INLINE ENGINES COMPARISON DIESEL VS. GAS 12L HD- GAS ENGINE < 190 bar PFP 11.5 Compression Ratio 64.8% Compression height 12L HD- DIESEL ENGINE 190 bar PFP 17 Compression Ratio 64.8% Compression height Johannes Andersen AVL MTC 19 november

36 Crank train Piston / Thermal AL 340 C to C STEEL Combustion bowl design important for system heat rejection (more heat rejection into head or piston) Alu piston could become borderline depending on combustion / bowl type Johannes Andersen AVL MTC 19 november

37 Crank train Piston / Combustion bowl AL Straight sided vs. Re-entrant STEEL STRAIGHT SIDED BOWL Lowest engine height Higher heat rejection to cylinder head Higher heat rejection into coolant RE-ENTRANT BOWL More space for oil cooling gallery at re-entrant bowl Higher heat rejection into piston Higher heat rejection into oil Johannes Andersen AVL MTC 19 november

38 CYLINDER HEAD STRUCTURE COMPARISON PARALLEL VALVE PATTERN VS. SKEWED VALVE PATTERN Comparison of Deformations " Advantages of Parallel Valve Pattern " Less deformation of cylinder head " Lower stress levels at the cylinder head at same load Comparison of Stresses " Shortest IN and EX ports # less heat transfer # best port quality " Advantages of Skewed Valve Pattern " Compact overhead design " Easy valve train " Mainly for Swirl system Johannes Andersen AVL MTC 19 november

39 CYLINDER HEAD STRUCTURE COOLING TOP DOWN COOLING Standard Flow Reverse Flow AVL patent Johannes Andersen AVL MTC 19 november

40 CYLINDER HEAD STRUCTURE COOLING Path for Temperature evaluation EX-EX j11 375kW_400l/min_2.5[bar]_90[C] j15 375kW_400l/min_2.5[bar]_90[C]Reverse Flow Temperature at measurement location (5[mm]): With the reverse flow concept the HTC are enlarged and therefore the temperature will drop at the location 5[mm] from the flame deck is 13[ C] Johannes Andersen AVL MTC 19 november

41 CYLINDER HEAD STRUCTURE VALVE SIZE & ANGLE Beta IN = 0,18 to 0,185 Beta EX = 0,152 to 0,165 Valveseat inner dia.[ mm] β = Enginebore mm [ ] 2 Number of valves " Intake valve could be bigger on gas engines due to lower PFP requirement. " Valve & Seat angles are reduced on NG engines compared to Diesel " Surface pressure target 80N/ mm² Johannes Andersen AVL MTC 19 november

42 ENGINE COOLING HEAT BALANCE Diesel, Full Load CNG Gas, Full Load Johannes Andersen AVL MTC 19 november

43 ENGINE COOLING WALL HEAT FLUX AND CUMULATIVE HEAT OF WALL AT LOW LOAD PART Piston Cylinder head Liner 43% 36% 21% Crank angle [ CA] Crank angle [ CA] " For pent-roof combustion chamber heat flux to cylinder head will dominate. Source: Daniel Ghebru, Thesis, KIT 2013 Johannes Andersen AVL MTC 19 november

44 BASE ENGINE LAYOUT CONSIDERATIONS! Bore/Stroke! Higher stroke/bore ratio gives! Shorter engine length! Less heat transfer to coolant! Lower stroke/bore ratio gives! Lower engine height! Lower friction (smaller bearing dia.)! Better volumetric efficiency! The stroke-to-bore ratio should be limited on the upper end, by a maximum mean piston speed velocity (9,0 m/s 10 m/s, max. 10,5 m/s) Johannes Andersen AVL MTC 19 november

45 ENGINE BREATHING SCE:! D x S = 170 mm x 210 mm! ε= 13! n = 1500 rpm Large bore engine experiments:! The earlier closing of the Miller valve timing results in longer ignition delays and a simultaneously lower increase in peak pressure! This extended ignition delay is caused by the lowered temperatures in the combustion chamber due to expansion! Shorter ignition delay for Atkinson due to higher turbulence and higher temperatures in the cylinder! Higher TKE level for Miller! Due to the high turbulent kinetic energy, the longer ignition delay of the lowered temperatures is slightly compensated! Therefore a higher knock resistance is seen for Miller concept Turbulent kinetic energy in the combustion chamber at the ignition timing Johannes Andersen AVL MTC 19 november