The Effect Of Intake Conditions On Formation Of Mixture And Combustion Of Premixed Compression Ignition Engine

With rapid economic development in China, the ownership of automobilemarket increased gradually. Cars make people convenient and result inenvironmental pollution and energy consumption at the same time. To meetfuture emission regulations, energy conservation and emissions reductionare necessary. By controlling the intake boundary conditions and couplinginjection strategy to optimize the combustion in cylinder are importantmeasures on emission reduction. On the other hand, the effect of fuelproperties on formation of mixture and combustion are very influential.The text bench of a high pressure common-rail diesel engine wasstudied and the EGR ratio was controlled by electronic EGR valve. The stateIV diesel was used as basic fuel, by adding different proportions ofgasoline, the wide distillation range fuels with differentphysicochemical properties were produced. The effects of EGR rate andinjection parameters on premixed compression ignition engine wereanalyzed in text bench. The results turned out that the wide distillationrange fuel can obviously increase ignition delay period and proportionof premixed combustion and meanwhile reduce nitrogen oxide and sootemissions. However, over-high percentage of gasoline can result in moreincomplete oxidation products and lower indicated thermal efficiency. Byadjusting the injection timing and CA50was controlled at5°CA ATDC, theindicated thermal efficiency of wide distillation range fuel showsinsensitive to EGR. Therefore, high EGR rate can be introduced to decreaseNOx emissions and keep relative high thermal efficiency. Besides, the sootemissions have a slightly increase. Improving injection pressure canincrease cylinder pressure and rate of heat release. With the increase of gasoline in wide distillation range fuel, the proportion of premixedcombustion increases, promoting better air-fuel mixture formation, whichcan reduce soot emissions. But the increase of incomplete oxidationproducts can reduce indicated thermal efficiency. Therefore, appropriateproportions should be selected to achieve better trade-off on fuel economyand emissions for the wide distillation range fuels.The effects of intake temperature and pressure and EGR on cylindermixture formation and combustion process were studied by CFD simulationplatform. The results turned out that increasing intake temperature canimprove cylinder average temperature, advancing combustion and heatrelease, but resulting in the increase of NOx and soot emissions. Theincrease of intake pressure can increase oxygen concentration in cylinderand remit the effect of EGR on ignition delay. The NOx emissions decreasedwith EGR increasing under different intake pressure, but high intakepressure resulted in less NOx emission under little EGR but produced moreNOx under medium EGR rates when compared with other pressures. With EGRrate increasing, the soot emission increases at first and then decreasesunder different intake pressures. The higher of the intake pressure, thebigger EGR rate when soot emission decreases.