Investigation of in-cylinder gas stratification of diesel engine during intake and compression stroke

Abstract

To control diesel emissions of NOx and PM (particular matter), there has been increasing interest in EGR (exhaust gas recirculation) stratification in recent years. However, only a few works have discussed in-cylinder distribution using two-dimensional EGR concentration contour. For a better understanding of in-cylinder stratification, a simulation study following stratified experimental investigation had been conducted to express in-cylinder local and global stratified distribution using OMC (oxygen mass concentration) contour and in-cylinder inhomogeneity. In this work, CO2 gas was selected to substitute for EGR. Two CO2 runners were mounted on tangential and helical intake port of a six-cylinder heavy duty diesel engine and manually controlled using a triple valve. CO2 stratification of supplying CO2 to one of the two intake ports (HelicalCO2 and TangentialCO2) and to both intake ports (BothCO2) has been discussed. The results indicate that HelicalCO2 and BothCO2 obtain high CO2 region at the lower periphery of the combustion chamber, TangentialCO2 obtain the same stratification when CO2 rate is 5%, while high CO2 region at the upper center of the combustion chamber as CO2 rate increasing. In the same way, global distribution from high to low temperature of TangentailCO2 has the highest in-cylinder inhomogeneity when CO2 rate is 5%, while HelicalCO2 becomes higher than other introduction strategies as CO2 rate increasing. Contrary to HelicalCO2 and BothCO2, TangentialCO2 obtains high CO2 at low temperature region when CO2 rate higher than 5%.