Internal Combustion Engine Group The effect of compression ratio on exhaust emissions from a PCCI Diesel engine ECOS July 2006 Laguitton, Crua, Cowell, Heikal, Gold

Introduction Experimental set-up Validation of single cylinder design Strategy for low NOx, soot and FC Conclusions Content

Highly pre-mixed and cool combustion IMPROVED AIR SYSTEM EFFICIENCY INCREASED IGNITION DELAY INCREASED EGR RATES AND TEMPERATURE MANAGEMENT ROBUSTNESS CONTROL IMPROVED AIR/FUEL MIXING REDUCED COMPRESSION RATIO COMBUSTION SYSTEM DESIGN ADVANCED AIR/EGR SYSTEMS ADVANCED COMBUSTION & AIR PATH CONTROL ADVANCED FIE TECHNOLOGY COLD START TECHNOLOGY REDUCE OXYGEN CONCENTRATION INCREASE EFFICIENCY +

Oxygen concentration Source: MTZ 11/2002: Toyota Temperature /(K) Local Equivalence Ratio Soot formation area NOx formation area Combustion trend to more pre-mixed and lower temperature Euro 4 – O 2 Concentration Map 100 % 85 % 70 % Level 3 – O 2 Concentration Map 100 % 85 % 70 % Approach is to reduce the oxygen concentration characteristics over the engine speed and load operating area: –Oxygen concentration in the flame is reduced –Less NOx are formed

SOC – Real SOI Injection period Low NOx strategy Improved air/fuel mixing to achieve low soot and good combustion efficiency Euro 4 Level 2 Level 3 Level of premixed fuel Increasing Load Trend is clear: -Injection durations reduced by increased injection pressure and nozzle flow -Ignition delay increased by changes to air/fuel, CR, intake temperature and EGR

Single cylinder engine facility Single cylinder – Ricardo HYDRA: –500cc swept volume (86mmx86mm) –2.0L high-flow head –Variable swirl ( Rs) –Compression Ratio 18.4:1 and 16.0:1 –Off-engine HP pump + common rail –Delphi injector –Delphi nozzle library –EmTronix FIE controller –Reference ultra low sulphur diesel fuel Test bed: –Horiba gas analyser MEXA 7100DEGR –AVL733 dynamic fuel meter –AVL415 variable sampling smoke meter –High speed data logger –Custom-built low speed data logger –TDM post processing Piston-bowl cross-sections

Validation of single cylinder design Full Load Results Part Load Results

Effect of compression ratio on NOx emissions 2000 rev/min 7.7 bar GIMEP LEVEL 2: CR 18.4 and CR 16.0: rev/min 10.8 bar GIMEP 2000 rev/min 7.7 bar GIMEP 1500 rev/min 3.0 bar GIMEP Reduced CR decreases NOx emissions especially at high loads. At low loads (1500 rev/min 3.0 bar GIMEP), slight improvements but combustion is already fully premixed, hence reduced benefits Fixed calibration

Effect of compression ratio on auto-ignition delay 2000 rev/min 10.8 bar GIMEP 2000 rev/min 7.7 bar GIMEP 1500 rev/min 3.0 bar GIMEP Reduced CR decreases in-cylinder pressures. Combustions occur later, increasing the level of premixed leading to higher maximum pressure variations but lower NOx

Late injection strategy for low NOx and soot Summary of single injection timing responses at 1500 rev/min 6.6 bar GIMEP (43% EGR rate, 1000 bar rail pressure) 19.0:1 AFR 17.0:1 AFR High FC penalty with very retarded single injections

DOE Model: Soot (g/h) Test data for FC (kg/h) DOE model: NOx (g/h)  NOx reduced by high EGR and low AFR  Low soot and good fuel consumption is achieved through improved air/fuel mixing -Low CR, swirl and rail pressure enhancement is critical  Good fuel consumption is achieved by optimising 50% burn after TDC. Late combustion is avoided by shortening combustion duration DOE modelling

Combustion phasing for optimum fuel consumption  Good combustion efficiency: -Rapid combustion -Centred between 0 and 10 °CA ATDC Test data for FC (kg/h)  This is a conflicting requirement with low NOx combustion strategies, which require slow and late combustion  A compromise to minimise impact on combustion efficiency is to operate: -Slow combustion -Well phased combustion

Conclusions  A good comparison with multi cylinder baseline results was achieved  Ultra low NOx has been achieved through highly pre-mixed and cool combustion  At 1500 rev/min, 3.0 bar GIMEP - a twin early injection strategy achieved improved HC and CO results compared to a pilot + “late” main strategy  At 1500 rev/min, 6.6 bar GIMEP - testing showed that a late injection strategy was essential for low NOx. A single late injection with high EGR achieved the best overall results  With 16:1 CR, an early injection strategy was only beneficial below 3.0 bar GIMEP. Late, high pressure injection combined with EGR is recommended  With the combustion bowl geometry tested, 10 and 12 hole nozzles did not offer an advantage at rated power. Reduced spray penetration, bowl interaction and air utilisation was detrimental at the higher loads and speed