Towards High Efficiency Engine THE Engine

Size: px

Start display at page:

Download "Towards High Efficiency Engine THE Engine"

Buck White
5 years ago
Views:

1 Towards High Efficiency Engine THE Engine Bengt Johansson Div. of Combustion Engines Director of KCFP, Lund University, Sweden

2 What is a high efficiency? Any text book on ICE: Ideal cycle with heat addition at constant volume: With a compression ratio, R c, of 60:1 and γ=1.4 we get an efficiency of 80,6% Why then do engines of today have an efficiency of 20-40%??? 2

3 Outline What is high efficiency? Combustion, thermodynamic, gas exchange and mechanical efficiencies. All four must be high. Combustion to enable high efficiency HCCI Partially Premixed Combustion Can we do something about engine design? Conclusions

4 Energy flow in an IC engine Brake Combustion * Thermodynamic * GasExchange * Mechanical FuelMEP Combustion efficiency QemisMEP QhrMEP QhtMEP Thermodynamic efficiency QlossMEP Gross Indicated efficiency IMEPgross QexhMEP Gas exchange efficiency PMEP Net Indicated efficiency lmepnet Mechanical efficiency FMEP Brake efficiency BMEP

5 Outline What is high efficiency? Combustion, thermodynamic, gas exchange and mechanical efficiencies. All four must be high. Combustion to enable high efficiency HCCI Partially Premixed Combustion Can we do something about engine design? Conclusions

6 HCCI -Thermodynamic efficiency Saab SVC variable compression ratio, VCR, HCCI, Rc=10:1-30:1; General Motors L850 World engine, HCCI, Rc=18:1, SI, Rc=18:1, SI, Rc=9.5:1 Scania D12 Heavy duty diesel engine, HCCI, Rc=18:1; Fuel: US regular Gasoline 6 SAE

7 All four efficiencies 7 SAE keynote Kyoto 2007

8 Net indicated efficiency= η C η T η GE +100% SI std SI high HCCI VCR Scania

9 Brake efficiency SI std SI high HCCI VCR Scania

10 Net indicated efficiency= η C η T η GE 47% SI std SI high HCCI VCR Scania

11 Outline What is high efficiency? Combustion, thermodynamic, gas exchange and mechanical efficiencies. All four must be high. Combustion to enable high efficiency HCCI Partially Premixed Combustion Can we do something about engine design? Conclusions

12 PPC - Diesel engine running on gasoline HCCI: η i =47% => PPC: η i =57% 60 Group 3, 1300 [rpm] Gross Indicated Efficiency [%] FR47333CVX FR47334CVX FR47336CVX Gross IMEP [bar] 12

13 Partially Premixed Combustion, PPC Spridare 8x0.12x90 & 8x0.12x150, Iso-oktan, CR-tryck 750 bar, Duration 0,6 ms = 3.6 CAD HCCI CI 5000 PPC HC [ppm] NOx [ppm] SOI [ATDC] Def: region between truly homogeneous combustion, HCCI, and diffusion controlled combustion, diesel SAE

14 Experimental setup, Scania D12 Bosch Common Rail Prail max 1600 [bar] Orifices 8 [-] Orifice Diameter 0.18 [mm] Umbrella Angle 120 [deg] Engine / Dyno Spec BMEPmax 15 [bar] Vd 1951 [cm3] Swirl ratio 2.9 [-] Fuel: Gasoline or Ethanol 14 SAE

15 Efficiencies 17.1: [%] Combustion Efficiency Thermal Efficiency Gas Exchange Efficiency Mechanical Efficiency Gross IMEP [bar] 15 SAE

16 [%] Efficiencies 14.3: Combustion Efficiency Thermal Efficiency Gas Exchange Efficiency Mechanical Efficiency Gross IMEP [bar] 16 SAE

17 Emissions NOx [g/kwh] Gross Net Brake EU VI US 10 Smoke [FSN] Gross IMEP [bar] Gross IMEP [bar] HC [g/kwh] Gross Net Brake EU VI US 10 CO [g/kwh] Gross Net Brake EU VI US Gross IMEP [bar] Gross IMEP [bar] 17

18 Emissions different fuels NOx [g/kwh] Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX Soot [FSN] Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX Gross IMEP [bar] Gross IMEP [bar] CO [g/kwh] Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX HC [g/kwh] Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX SAE Gross IMEP [bar] Gross IMEP [bar] 18

19 Efficiency with Diesel or Gasoline Average improvement of 16.6% points at high load by replacing diesel fuel with gasoline! D13 Gasoline D13 Diesel Brake Efficiency [%] Gross IMEP [bar] D13 Diesel was calibrated by Scania to meet EU V legislation. 19

20 Gross Indicated Efficiency [%] High dilution is needed for high indicated efficiency FR47338CVX FR47335CVX FR47334CVX 10%! SAE paper Abs Inlet Pressure [bar]

21 Turbo System Efficiency Requirement W compressor W _ ideal compressor turbine mechanical turbine_ ideal 55 global Minimum Turbo Global Efficiency [%] Gross IMEP [bar] 21

22 Outline What is high efficiency? Combustion, thermodynamic, gas exchange and mechanical efficiencies. All four must be high. Combustion to enable high efficiency HCCI Partially Premixed Combustion Can we do something about engine design? Conclusions

23 ICE research in Lund vs. time CCV=Cycle to Cycle Variations in Spark Ignition Engines GDI= Gasoline Direct Injection 2-S= Two Stroke engine VVT=Variable Valve Timing HCCI=Homogeneo us Charge Compression Ignition SACI=Spark Assisted Compression Ignition PPC= Partially Premixed Combustion

24 High efficiency thermodynamics: Simulation results from GT-power Indicated efficiency 65,2% Brake efficiency 60.5%

25 Any text book on ICE: Is 65% possible? Ideal cycle with heat addition at constant volume: With a compression ratio of 60:1 and γ=1.4 we get an efficiency of 80,6% 25

26 There are a few drawbacks 1000 Peak cylinder pressure as function of compression ratio Peak cylinder pressure [bar] Lambda = 1.2 Lambda = 3.0 Engine structure must be very robust (if at all possible) Very high friction and hence lower mechanical efficiency Compression ratio 26

27 There are a few drawbacks Thermodynamic efficiency as function of compression ratio 90 No heat transfer losses 80 With heat transfer losses (Woschni) Thermodynamic efficiency [%] Compression ratio 27

28 How then make 60:1 usable? Swedish proverb: Den late förtar sig hellre än går två gånger Which according to google translate means: The lazy man rather breaks his back than walk twice 28

29 How about Take it in steps! 60 = If we divide the compression in two equal stages the total pressure (and temperature) ratio will be the product of the two 7.75:1 x 7.75:1=60:1 With a peak pressure of 300 bar the pressure expansion ratio is 300:1 and hence 300^(1/1.4)= in volume ratio (gamma=1.25 during expansion gives 96:1) 29

30 Split cycles from the past 30

31 From history: Compound Engine Divide the expansion in three cylinders with same force, F, on each piston. The smaller cylinder has higher pressure but also smaller area F=p*A 31

32 32

33 Split cycles from the present 33

(up to 30 bar) results with two-stage turbo Peak pressure 200 bar F. Steinparzer, W. Stütz, H.

34 Three step compression in production To run a smaller engine at higher load turbocharging is used. The engine is using two or three shafts of which only one can generate power High BMEP (up to 30 bar) results with two-stage turbo Peak pressure 200 bar F. Steinparzer, W. Stütz, H. Kratochwill, W. Mattes: Der neue BMW-Sechzylinder-Dieselmotor mit Stufenaufladung, MTZ, 5,

Design criteria of engines today Non-turbo SI engines Load range 0-12 bar BMEP Peak pressure during the cycle 65-70 bar Highly

35 Design criteria of engines today Non-turbo SI engines Load range 0-12 bar BMEP Peak pressure during the cycle bar Highly turbocharged engines Load range 0-30 bar BMEP Peak pressure during the cycle bar Friction FMEP bar Friction FMEP bar 35

36 Divide the process into two cylinders Low pressure cycle Use large naturally aspirated engine designed for 30 bar peak pressure High pressure cycle Use small engine with 300 bar peak pressure feed by the large engine Load range 0-5 bar BMEP Peak pressure during the cycle 30 bar Load range bar BMEP Peak pressure during the cycle bar Friction FMEP bar Friction FMEP bar 36

37 Principle layout 2 stroke- 4 stroke- 2 stroke 37

Pressure Operating cycle 2+4+2 stroke Combustion TDC Inlet 1 Compression Compression BDC Inlet TDC Expansion Compression BDC Exhaust Inlet

38 Pressure Operating cycle stroke Combustion TDC Inlet 1 Compression Compression BDC Inlet TDC Expansion Compression BDC Exhaust Inlet TDC 4 1 BDC TDC Expansion BDC TDC 4 Expansion 3 Exhaust Exhaust BDC TDC BDC TDC Expansion Exhaust Inlet Compression TDC BDC TDC BDC TDC 38

39 Principle layout 4 stroke + 4 stroke 39

Pressure Operating cycle 4 + 4 stroke Combustion TDC Inlet 1 Compression Compression BDC Expansion TDC Expansion BDC Exhaust 4 TDC 4 1

40 Pressure Operating cycle stroke Combustion TDC Inlet 1 Compression Compression BDC Expansion TDC Expansion BDC Exhaust 4 TDC 4 1 Exhaust Inlet BDC TDC BDC TDC Exhaust 2 Inlet Compression Expansion 2 BDC TDC BDC TDC 3 3 Expansion Exhaust Inlet Compression TDC BDC TDC BDC TDC 40

41 DOUBLE COMPRESSION EXPANSION ENGINE CONCEPTS: A PATH TO HIGH EFFICIENCY Nhut Lam, Martin Tunér, Per Tunestål, Bengt Johansson, Lund University Arne Andersson, Staffan Lundgren, Volvo Group SAE

42 Conceptual design 4-4 SAE

43 Simulation setup, DCEE concept - 2 models SAE Unit DCEE λ=1.2 DCEE λ=3.0 Bore, HP cylinder mm 95 Stroke, HP cylinder mm 100 HP-cylinder displacement dm CR, HP cylinder :1 Bore, LP cylinder mm Stroke, LP cylinder mm 100 LP-cylinder displacement dm CR, LP cylinder - 100:1 EGR % 0 CAC temperature K 350 No intercooling Simulation engine speed rpm

44 High Pressure cylinder SAE

45 Low Pressure cylinder SAE

46 Combined SAE

47 Heat Transfer To reduce heat transfer: Reduce heat transfer coeff., h Reduce surface area, A Reduce gas temperature Increase wall temperature 47

48 0.35 Wall surface area Wall surface area as function of cylinder volume Area [m 2 ] DCEE, lambda 1.2 DCEE, lambda 3.0 CI, lambda 1.2 CI, lambda SAE Cylinder volume [dm 3 ] 48

49 Area/volume-ratio Wall surface area per volume as function of cylinder volume DCEE, lambda 1.2 DCEE, lambda 3.0 CI, lambda 1.2 CI, lambda 3.0 Area/Volume [m 2 /m 3 ] SAE Cylinder volume [dm 3 ] 49

50 Heat transfer losses 50

51 Estimation of friction mean effective pressure, FMEP FMEP as function of PCP Friction is assumed to scale with Peak Cylinder Pressure, P max FMEP assumed to be 1.2 bar P max HP cylinder, DCEE-concept FMEP [bar] LP cylinder, DCEE-concept Traditional heavy duty turbocharged CI engine Naturally aspirated 2300 rpm Designed engine peak cylinder pressure PCP [bar] SAE

52 Mechanical losses Unit DCEE, λ=1.2 DCEE, λ=3.0 Conventional, λ=1.2 Conventional, λ=3.0 Peak cylinder pressure -LP cylinder bar HP cylinder bar 300 FMEP -LP cylinder bar HP cylinder bar 1.8 Total FMEP bar Net indicated work, IMEP n bar Mechanical efficiency % SAE

53 Resulting Efficiencies SAE

54 Summary HCCI has shown high efficiency Up to 100% improvement in indicated efficiency vs. standard SI combustion Modest combustion efficiency HCCI peaks at 47% indicated efficiency at around 6 bar BMEP PPC has shown higher fuel efficiency Indicated efficiency of 57% at 8 bar IMEP Indicated efficiency of 55% from 5-18 bar IMEP With 70 RON fuel we can operate all the way from idle to 26 bar IMEP With an effective compression/expansion ratio of 60:1 the split cycle concept shows 62% indicated/ 56% brake efficiency potential h T =1-1 R c g-1 54

55 High Efficiency Combustion Engines What is the limit? It all starts at 40 and ends at 60 (% engine efficiency that is, not life) Prof. Bengt Johansson Lund University

56 Thank you! 56

57 Towards High Efficiency Engine THE Engine Bengt Johansson Div. of Combustion Engines Director of KCFP, Lund University, Sweden

Future fuels. by Bengt Johansson. Clean combustion research center KAUST

Future fuels. by Bengt Johansson. Clean combustion research center KAUST Future fuels by Bengt Johansson Clean combustion research center KAUST Future fuels Energy Source Energy carrier Energy usage Well to Tank Tank to Wheel Well to Wheel 2 Conventional path Crude Oil η =