The effect of combustion type on exhaust emissions and thermal efficiency at partial load operating condition in heavy duty diesel engines

Abstract

In heavy duty diesel engines, reductions of exhaust emissions and improvement in thermal efficiency have been strongly required from a view point of the prevention of air pollution and global warming. Premixed charge compression ignition (PCCI) can reduce NOx and Smoke simultaneously at partial load operating conditions in a diesel engine, and this type of combustion has been studied for a long time because it has the potential to reduce exhaust emissions compare to the conventional diesel combustion. Meanwhile, conventional diesel combustion (diffusion combustion) can also achieve low NOx and Smoke level by combining with high rate EGR and high fuel injection pressure in the past decade. In this paper, such conventional diesel combustion is referred to as the low temperature diesel combustion (LTDC). Although each combustion type has the characteristic regarding exhaust emissions and thermal efficiency in a diesel engine, there are few reports which investigated the effect of the difference between PCCI and LTDC on exhaust emissions and thermal efficiency in a modern heavy duty diesel engine. In this study, the experiments conducted to compare the exhaust emissions and thermal efficiency between PCCI and LTDC at brake mean effective pressure = 0.4 MPa in the heavy duty single cylinder diesel engine. For comparison of PCCI and LTDC, swirl ratio and fuel injection pressure that strongly effect on combustion was optimized in each combustion type. As the result of an experiment, it was found that the improvement of NOx by PCCI is large compared to LTDC, although PCCI has the problem to be solved such as the improvement of brake thermal efficiency.

Keywords

• heat engine
• compression ignition engine
• efficiency
• fuel economy
• premixed charge compression ignition
• diesel combustion