Study On Fuel Economy Of A High Compression Ratio Miller Engine With EGR

Combined with variable valve timing technology and late intake valve close offMiller cycle engine has the following advantages, such as the geometrical compressionratio is high, the expansion ratio is high, the fuel economy is good, effectivelysuppress knocking, dramatically reducing NOx emissions and other advantages.This study on a port injection1.6L inline four-cylinder gasoline engine, throughdress the intake camshaft and combine with variable valve timing mechanism toachieve late intake valve close Miller cycle, as well as the Miller cycle facelift highercompression ratio piston and the compression ratio is12.6and13.5. Comparativeanalysis of the external characteristics which Miller cycle engine with the originalengine with universal characteristic, as well as three operating cycle combustioncharacteristics in a typical operating point. The installation of an external EGR systemon this basis, research effect of the combustion characteristics, fuel economy andemission characteristics in Miller cycle engine with the external EGR.Comparison of external characteristics with Miller cycle engine (the compressionratio is12.6) and the original engine (the compression ratio is10.4) in the low speedrange torque output decreased slightly, but not more than5%decline; When the speedis in the high speed region, Miller cycle engine torque output is slightly more than theoriginal engine, and the compression ratio of13.5Miller cycle engine power decreasedsignificantly, After the engine through the air compressor to pressurize the intake ofthe engine power to restore a significant effect, After10kPa supercharged Miller cyclein13.5compression ratio has been close to the external characteristics of the externalcharacteristics of the original machine, After20kPa supercharged Miller cycle in13.5compression ratio has been in full over the external characteristics of the externalcharacteristics of the original machine.The fuel consumption of Miller cycle in the effective rate is lower than all theconditions of the original machine. But the effective rate of fuel consumption the improvement of in the low speed and the low load region is smaller than theimprovement of the high load region and the high rotational speed. Comparison of theeffective compression ratio with Miller cycle and original engine. We can be found theeffective compression ratio of Miller cycle in the low-speed, low-load range is lowerthan the original engine, but in the high speed and high load region is not.After the installation of the engine EGR, the first decline after rising fueleconomy. With the growth of EGR rate, the engine thermal efficiency has increasedafter the first decline. With the EGR rate, the ignition advance angle increases, theengine exhaust advance competing small gradient expansion ratio increases. Postponethe engine while the exhaust valve opens, the intake and exhaust valve overlapincreases door, Cylinder temperature is reduced, NOx emissions decrease, HCemission is increase, HC emission is reduce.The specific fuel consumption of Miller cycle that compression ratio is12.6withEGR is lower than the original engine with EGR. And the fuel consumption of Millercycle and the original engine are showing an upward trend after the drop,The fuelconsumption point corresponding to the optimum EGR rate of Miller cycle is less thanthe original engine. Miller cycle for EGR tolerated better than the original machine. Inall load conditions with increasing EGR rate, NOx emissions decreased sharply, emitless than the original engine. In various load conditions, HC emissions with increasingEGR rate and increased emissions higher than the original. Variation of CO emissionsunder different load conditions vary greatly, emissions higher than the original.The fuel consumption of Miller cycle engine that compression ratio is13.5. withEGR is lower than the original but the compression ratio is12.6Miller cycle engine.After the installation of EGR, the engine which compression ratio is13.5tolerancecompared to12.6fall. The Miller cycle engine with EGR and13.5compression ratiocan effectively reduce NOx emissions below the compression ratio12.6Miller cycle.However, CO and HC of the Miller cycle which compression ratio is13.5is higherthan the12.6Miller cycle engine.