عنوان مقاله [English]
Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion trend in terms of high thermal efficiency and low emissions. It is difficult to control autoignition and combustion because they are controlled primarily by the chemical kinetics of air/fuel mixture. In this study, a homogeneous mixture of natural-gas and air was used in a compression ignition engine to reduce NOx emissions and improve thermal efficiency. In order to control ignition timing and combustion, a small amount of Dimethyl Ether (DME) was mixed with the natural-gas. In this paper, a multi-dimensional computational fluid dynamics (CFD) model coupled with chemical kinetics mechanisms was applied to investigate the effects of various temperatures, pressures, equivalence ratios and fuel compositions on the combustion performance and emission characteristics of an HCCI engine. The mixture could run the engine quietly and smoothly over a wide range of loads. Under the present test conditions, finite amount of DME was necessary in order to achieve ignition of the mixture. In addition, thermal efficiency was higher than that of methane fueled engine, when the DME proportion was optimized. NOx emissions were extremely low, however, the emissions of total unburned hydrocarbon were high.