Effect of Homogeneous Stratified Mixture Combustion on Performance and Emissions of a Spray-Guided GDI Engine - A CFD Study 2020-01-0785
Gasoline direct injection (GDI) engine uses stratified mixture at part-load conditions and homogeneous mixture at full-load conditions. But at part-loads, soot emissions are found to be high because of improper air-fuel mixing. To overcome this, homogenous-stratified mixture (a combination of overall homogeneous lean mixture with a combustible mixture at the location of the spark plug) is found to be better to reduce soot emissions compared to stratified mixture mode. It will also help reduce fuel consumption. Therefore, in the present study, an attempt has been made to analyse the effect of homogenous-stratified mixture mode on the performance and emission characteristics of a spray-guided GDI engine. In the analysis, an overall equivalence ratio varied from 0.5-0.8. Two direct fuel injections (the first in suction stroke and the second in the compression stroke) are used to get homogeneous-stratified mixture. The split ratios among the injections in percentage are 20-80%, 30-70%, 40-60% and 50-50%. The fuel is injected at the pressure of 200 bar with 6-hole solid cone injector. The CFD analysis using CONVERGE software is performed at a constant engine speed of 2000 rev/min. The CFD models used in this study are validated with the available experimental data in the literature. The engine specifications and boundary conditions are taken from the literature. The SAGE model, the detailed soot model (PM soot model), the KH-RT model, and the Frossling model are used for the analysis of the combustion, soot formation, fuel spray breakup, and fuel evaporation respectively. The effects of equivalence ratio and fuel split-ratios on mixture distribution, flame propagation, heat release rate, indicated mean effective pressure (IMEP), soot, hydrocarbon and nitrogen oxide emissions will be discussed. More details will be given in the manuscript.
Keywords: Split injection, homogenous stratified mode, GDI engine, CFD.