Effect of EGR and preheating on natural gas combustion assisted with gas-oil in a diesel engine

In order to reduce NO_x and smoke simultaneously and also to improve markedly the trade-off between smoke and NO_x without deteriorating fuel consumption, natural gas was charged homogeneously into the intake air and was burned igniting by a small amount of gas oil injection in a four cylinder naturally-aspirated DI diesel engine. Combustion tests were carried out by changing the ratio of the amount of natural gas and the amount of gas oil first, secondarily the intake preheating temperature, and thirdly the EGR rate respectively. Effects of the respective parameter on the ignition and the burning rate of natural gas, exhaust emissions and specific fuel consumption were clarified experimentally. It is found that significant improvement of smoke-NO_x trade-off can be obtained without deteriorating fuel consumption by the suitable combination between the natural gas charge rate, the intake preheating temperature and the EGR rate for each engine load condition.