An effect of injection strategy on mixture formation and combustion characteristics of a PCCI engine

Abstract

As the demand for automobiles with lower emissions and higher thermal efficiency has been increased worldwide, diesel engines which have high thermal efficiency and a low CO2 level are becoming more attractive. However in case of the diesel engines, increased emissions such as NOx and particulate matter are emerging as problems. Thus, many kinds of methods have been studied to solve these problems. As one of the methods, premixed diesel engines have been suggested. Especially PCCI (Premixed Charge Compression Ignition) combustion system, which can mix the air and fuel sufficiently using early injection and then ignites a lean and uniform homogeneous charge, is drawing attention. Early studies have shown that in a PCCI engine, the fuel injection timing and spray angle affect the mixture formation and combustion. Therefore the purpose of this research is to study the spray and combustion characteristics in a PCCI engine and further more to investigate the effect of injection conditions such as injection timings and times using Narrow Angle Direct Injection(NADI) injector on mixture formations and combustion. As a result, in case of single injection, at 100° spray cone angle and 65° injection timing, the characteristics of IMEP and smoke characteristics were better than others because the mixture became more homogeneous. And as the injection times increased, the fuel evaporation rate increased and we could get higher IMEP and still low smoke levels. From this study, we found that the fuel injection timing largely affected the mixture formation and combustion in the PCCI engine and multiple injection method showed better effects on combustion because of the higher evaporation rate.