Effects of a three-stage split injection on Hydrocarbon (HC) emissions of a CNG engine during hot start in the stratified mode

摘要

An attempt was made to employ the three-stage split injection for obtaining compact spray cloud and reduction in HC emissions from a single-cylinder CNG engine during hot start. The HC emission characteristics for various parameters including the injection timing, the split ratio, etc were investigated experimentally. It has been found that desirable stratified mixture distribution achieved by the three-stage split injection can significantly improve the engine-out HC emissions. It is possible to obtain stable combustion and low levels of peak HC emissions during starts at an excess air ratio of 0.96 and a split ratio of 3:1:1. Additionally, the two close-coupled injections during compression stroke yielded marked reduction in the peak HC when the time interval is about 26°CA.