Towards High Efficiency Engine THE Engine

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

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

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

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

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 SAE2006-01-0205

All four efficiencies 7 SAE keynote Kyoto 2007

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

Brake efficiency SI std SI high HCCI VCR Scania

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

PPC - Diesel engine running on gasoline HCCI: η i =47% => PPC: η i =57% 60 Group 3, 1300 [rpm] Gross Indicated Efficiency [%] 55 50 45 40 35 30 25 FR47333CVX FR47334CVX FR47336CVX 20 0 2 4 6 8 10 12 14 Gross IMEP [bar] 12

Partially Premixed Combustion, PPC Spridare 8x0.12x90 & 8x0.12x150, Iso-oktan, CR-tryck 750 bar, Duration 0,6 ms = 3.6 CAD 6000 1200 HCCI CI 5000 PPC 1000 4000 800 HC [ppm] 3000 2000 600 400 NOx [ppm] 1000 200-180 -160-140 -120-100 -80-60 -40-20 SOI [ATDC] Def: region between truly homogeneous combustion, HCCI, and diffusion controlled combustion, diesel SAE 2004-01-2990 13

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 2009-01-2668

Efficiencies 17.1:1 100 95 90 85 [%] 80 75 70 65 60 55 Combustion Efficiency Thermal Efficiency Gas Exchange Efficiency Mechanical Efficiency 50 4 5 6 7 8 9 10 11 12 13 Gross IMEP [bar] 15 SAE 2009-01-2668

[%] Efficiencies 14.3:1 100 95 90 85 80 75 70 65 60 55 Combustion Efficiency Thermal Efficiency Gas Exchange Efficiency Mechanical Efficiency 50 4 6 8 10 12 14 16 18 Gross IMEP [bar] 16 SAE 2010-01-0871

Emissions NOx [g/kwh] 0.6 0.5 0.4 0.3 0.2 0.1 Gross Net Brake EU VI US 10 Smoke [FSN] 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 2 4 6 8 10 12 14 16 18 Gross IMEP [bar] 0 4 6 8 10 12 14 16 18 Gross IMEP [bar] 1.5 10 HC [g/kwh] 1.2 0.9 0.6 Gross Net Brake EU VI US 10 CO [g/kwh] 9 8 7 6 5 4 Gross Net Brake EU VI US 10 3 0.3 2 0 2 4 6 8 10 12 14 16 18 Gross IMEP [bar] 17 1 0 2 4 6 8 10 12 14 16 18 Gross IMEP [bar] 17

Emissions different fuels NOx [g/kwh] 0.5 0.45 0.4 0.35 0.3 0.25 0.2 Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX Soot [FSN] 2.5 2 1.5 1 Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX 0.15 0.1 0.5 0.05 0 2 4 6 8 10 12 14 16 18 20 Gross IMEP [bar] 0 2 4 6 8 10 12 14 16 18 20 Gross IMEP [bar] CO [g/kwh] 12 10 8 6 4 Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX HC [g/kwh] 10 9 8 7 6 5 4 3 Ethanol FR47330CVX FR47331CVX FR47333CVX FR47334CVX FR47335CVX FR47336CVX FR47338CVX SAE 2010-01-0871 2 0 2 4 6 8 10 12 14 16 18 20 Gross IMEP [bar] 2 1 0 2 4 6 8 10 12 14 16 18 20 Gross IMEP [bar] 18

Efficiency with Diesel or Gasoline Average improvement of 16.6% points at high load by replacing diesel fuel with gasoline! 52 50 48 D13 Gasoline D13 Diesel Brake Efficiency [%] 46 44 42 40 38 36 34 5 10 15 20 25 30 Gross IMEP [bar] D13 Diesel was calibrated by Scania to meet EU V legislation. 19

Gross Indicated Efficiency [%] 58 56 54 52 50 48 46 High dilution is needed for high indicated efficiency FR47338CVX FR47335CVX FR47334CVX 10%! SAE paper 2010-01-1471 44 1.5 2 2.5 3 3.5 Abs Inlet Pressure [bar]

Turbo System Efficiency Requirement W compressor W _ ideal compressor turbine mechanical turbine_ ideal 55 global Minimum Turbo Global Efficiency [%] 50 45 40 35 30 25 20 15 10 5 0 4 6 8 10 12 14 16 18 Gross IMEP [bar] 21

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 1990 1995 2000 2005 2010 2015 23

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

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

There are a few drawbacks 1000 Peak cylinder pressure as function of compression ratio Peak cylinder pressure [bar] 900 800 700 600 500 400 300 200 100 Lambda = 1.2 Lambda = 3.0 Engine structure must be very robust (if at all possible) Very high friction and hence lower mechanical efficiency 0 0 10 20 30 40 50 60 70 Compression ratio 26

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 [%] 70 60 50 40 30 20 0 10 20 30 40 50 60 70 Compression ratio 27

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

How about Take it in steps! 60 = 7. 75 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)=58.8.1 in volume ratio (gamma=1.25 during expansion gives 96:1) 29

Split cycles from the past 30

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

Split cycles from the present 33

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, 5,2005 34

Design criteria of engines today Non-turbo SI engines Load range 0-12 bar BMEP Peak pressure during the cycle 65-70 bar Highly turbocharged engines Load range 0-30 bar BMEP Peak pressure during the cycle 180-230 bar Friction FMEP 0.25-0.5 bar Friction FMEP 1.2-2 bar 35

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 35-80 bar BMEP Peak pressure during the cycle 250-300 bar Friction FMEP 0.05-0.1 bar Friction FMEP 1.2-2.2 bar 36

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 TDC 4 1 BDC TDC Expansion BDC TDC 4 Expansion 3 Exhaust Exhaust BDC TDC BDC TDC 2 2 3 Expansion Exhaust Inlet Compression TDC BDC TDC BDC TDC 38

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 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

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 2015-01-1260

Conceptual design 4-4 SAE 2015-01-1260 42

Simulation setup, DCEE concept - 2 models SAE 2015-01-1260 Unit DCEE λ=1.2 DCEE λ=3.0 Bore, HP cylinder mm 95 Stroke, HP cylinder mm 100 HP-cylinder displacement dm 3 0.71 CR, HP cylinder - 11.5:1 Bore, LP cylinder mm 317 249 Stroke, LP cylinder mm 100 LP-cylinder displacement dm 3 7.9 4.9 CR, LP cylinder - 100:1 EGR % 0 CAC temperature K 350 No intercooling Simulation engine speed rpm 1900 43

High Pressure cylinder SAE 2015-01-1260 44

Low Pressure cylinder SAE 2015-01-1260 45

Combined SAE 2015-01-1260 46

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

0.35 Wall surface area Wall surface area as function of cylinder volume 0.3 0.25 Area [m 2 ] 0.2 0.15 0.1 0.05 DCEE, lambda 1.2 DCEE, lambda 3.0 CI, lambda 1.2 CI, lambda 3.0 0 0 1 2 3 4 5 6 7 8 9 SAE 2015-01-1260 Cylinder volume [dm 3 ] 48

1200 1000 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 ] 800 600 400 200 0 0 1 2 3 4 5 6 7 8 9 SAE 2015-01-1260 Cylinder volume [dm 3 ] 49

Heat transfer losses 50

Estimation of friction mean effective pressure, FMEP 1.8 1.6 1.4 FMEP as function of PCP Friction is assumed to scale with Peak Cylinder Pressure, P max FMEP assumed to be 1.2 bar @200 bar P max HP cylinder, DCEE-concept FMEP [bar] 1.2 1 0.8 LP cylinder, DCEE-concept Traditional heavy duty turbocharged CI engine 0.6 0.4 0.2 Naturally aspirated SI-engine @ 2300 rpm 0 0 50 100 150 200 250 300 Designed engine peak cylinder pressure PCP [bar] SAE 2015-01-1260 51

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 36 16 -HP cylinder bar 300 FMEP -LP cylinder bar 0.21 0.09 -HP cylinder bar 1.8 Total FMEP bar 0.34 0.31 1.8 Net indicated work, IMEP n bar 8.8 4.3 12.9 6.3 Mechanical efficiency % 96.1 92.8 86.0 71.6 SAE 2015-01-1260 52

Resulting Efficiencies SAE 2015-01-1260 53

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

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

Thank you! 56

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