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Internal Combustion Engine Group

Internal Combustion Engine Group. The effect of compression ratio on exhaust emissions from a PCCI Diesel engine. ECOS 2006 12-14 July 2006. Laguitton, Crua, Cowell, Heikal, Gold. Content. Introduction Experimental set-up Validation of single cylinder design

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Internal Combustion Engine Group

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  1. Internal Combustion Engine Group The effect of compression ratio on exhaust emissions from a PCCI Diesel engine ECOS 2006 12-14 July 2006 Laguitton, Crua, Cowell, Heikal, Gold

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

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

  4. 10 Soot formation area 9 8 7 6 5 Local Equivalence Ratio 4 3 2 1 1000 1400 1800 2200 2600 3000 Temperature /(K) Combustion trend to more pre-mixed and lower temperature NOx formation area Source: MTZ 11/2002: Toyota Oxygen concentration Euro 4 – O2 Concentration Map 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 70 % 85 % 100 % Level 3 – O2 Concentration Map 70 % 85 % 100 %

  5. Low NOx strategy Level of premixed fuel Improved air/fuel mixing to achieve low soot and good combustion efficiency Euro 4 Level 2 Level 3 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 SOC – Real SOI Injection period

  6. Single cylinder engine facility Single cylinder – Ricardo HYDRA: • 500cc swept volume (86mmx86mm) • 2.0L high-flow head • Variable swirl (1.0-3.5 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

  7. Validation of single cylinder design Full Load Results Part Load Results

  8. Effect of compression ratio on NOx emissions Fixed calibration 2000 rev/min 7.7 bar GIMEP LEVEL 2: CR 18.4 and CR 16.0:1 2000 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

  9. 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

  10. 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) High FC penalty with very retarded single injections 19.0:1 AFR 17.0:1 AFR

  11. DOE model: NOx (g/h) DOE Model: Soot (g/h) Test data for FC (kg/h) DOE modelling • 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

  12. Test data for FC (kg/h) Combustion phasing for optimum fuel consumption • Good combustion efficiency: • Rapid combustion • Centred between 0 and 10 °CA ATDC • 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

  13. 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

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