A Mixed Numerical-Experimental Analysis for the Development of a Partially Stratified Compressed Natural Gas Engine

This paper discusses a partially stratified technology for engines running lean on natural gas. A single cylinder research engine has been modified to enable direct injection of a small quantity of natural gas through the spark plug to the region of the electrodes, independent of the overall lean homogeneous charge. Thus, a Partially Stratified Charge (PSC) is formed within the chamber allowing significant extension of the lean limit of combustion. Although PSC has been shown to reduce NO_X emissions and improve combustion efficiency, high hydrocarbon emissions have been observed and this was thought to be due to poor mixing of the injected fuel air charge.

The mixed experimental-numerical activity described herein, carried out by the Universities of British Columbia of Vancouver and Roma Tor Vergata, is aimed at improving the micro-direct injection PSC process. The numerical study has enabled a detailed analysis of the fluid dynamics and combustion processes in the region of the electrodes, early in the combustion cycle. The model has been verified using experimental data from the single cylinder research engine. The results suggest that improving mixing of the PSC (by changing the way it is injected into the combustion chamber) can significantly reduce NO_X. A multi-hole injection concept has been designed and numerically tested, indicating a potential improvement in both performance and emissions.