Numerical Simulation On Combustion Process Of DME Engine

Energy is set on a country's economic lifeline. Fossil fuels, such as gasoline, natural gas are non-renewable resources. At the same time, with the increasing auto possession, the exhaust emission has become a main pollutant in urban air. Thus, every country is studying-actively to develop clean and efficient auto alternative fuels. Dimethyl ether (DME)'s formula is CH3OCH3, as without C-C key, the molecule of DME is good for reducing the soot.With a low boiling point as well, DME is beneficial for the formation of cylinder mixture. Simultaneously, with a high hexadecane value, the ignition property is better than diesel. Homogeneous Charge Compression Ignition (HCCI),which first injects even gas mixture formed by the air and fuel, then the mixture gets to the autoignition phase when the temperature of mixture reached the ignition point with the piston compressing, so it can apply larger compression ratio and has high thermal efficiency. Thus it is necessary to go further study on DME HCCI engine.In this paper, the ZS1100 diesel engine was used as the prototype, with appropriate changes, a 3D engine geometric model was created by CAD, then was meshed in Gambit and was coupled with the simplified DME ether reaction mechanism created by CHEMKIN in FLUENT, thus a DME HCCI engine model of 3d CFD (computational fluid dynamics) was constructed. With iterating to simulation, the burning process of DME HCCI and the influence of different operation parameters on the combustion characteristics were studied. The research content and conclusions are as follows:1 The temperature, pressure and components of scores during the combustion process. are analyzed. Research shows that:the DME HCCI are divided into three stages, (1) the low-temperature combustion stage, main is the H was taken off from the DME and the DME becomes CH3OCH2, then with twice oxygenation, the CH3OCH2 becomes O2CH2OCH2O2H.(2) the negative temperature coefficient stage, whenβcrack happens on CH2OCH2O2, two molecular HCHO and one molecular OH are generated. (3) the high temperature stage, the HCHO is gradually oxidated and the CO2 and NO are generated. At this time the cylinder's pressure and temperature are both at their maximum.2 The influence of different operation parameters on the combustion for DME HCCI. is analyzed.(1) the influence of intake air temperature:as the intake air temperature raises, the top burning temperature also increases. But the maximum combustion pressure drop instead. Because of the rising combustion temperature, the NO discharge also increases.(2) the influence of equivalence ratio:when the equivalence ratio raises, the top burning temperature and the maximum combustion pressure of the cylinder both go higher, the NO discharge increases as well. (3) the influence of compression ratio:with the increase of compression ratio, the top burning temperature and the maximum combustion pressure also increase, thus cause the increasing of the NO emission.(4) the influence of crank speed:as the crank speed increases, the top combustion temperature and maximum combustion pressure are significantly increased, but when the crank speed continues to increase, they both become smaller.