Experimental And Numerical Investigation On The Combustion And Emission Characteristics Of Partially Premixed Compression Ignition (PPCI) In A Heavy Duty Diesel Engine

Partially premixed compression ignition (PPCI) in diesel engine is a combustionmode between diffusion combustion and HCCI combustion, whose combustioncontrollability and emission performance gets close to HCCI combustion engine, thepremixed duration plays a key role in realizing PPCI.PPCI combustion in a boosted six-cylinder heavy duty diesel engine is realized byadjusting injection timing and the rate of EGR based on single injection. The effects ofinjection timing, EGR, injection pressure and load rate on combustion and heat releasepattern are studied. The results show that both early and late injection have long premixedduration, which is helpful to form more homogeneous mixture, and no diffusioncombustion is found in heat release rate curve. Premixed combustion and low temperaturecombustion are the key factors to reduce PM and NOxsimultaneously. However, the lowtemperature combustion and dilute mixture may lead to incomplete combustion, andconsequently, at relatively late injection conditions, HC and CO emissions increasedramatically, fuel consumption gets worse. In these partially premixed combustionpatterns, the effect of injection pressure on PM and NOxemission doesn’t work obviously.When the engine load rate is increased to50%, diffusion combustion appear in earlyinjection modes, which lead more NOxand PM emissions.With the data measured by experiments, such as fuel consumption, intake air pressure,EGR ratio and so on, as initial inputs of simulation program, and the equivalence ratio andtemperature distribution in the cylinder can be calculated out. With the simulation results,it was found out that, the fuel and air of PPCI mix better than that of the normal diffusioncombustion, which leads lower soot emission; the combustion temperature can be reducedsignificantly with the introduce of EGR, and the NOx emission decreases a lot.