【摘要】 使用KIVA-3V对增压柴油机和二甲醚发动机标定功率点的缸内燃烧过程与NOx排放进行了数值模拟研究。研究结果表明:计算所得的气缸压力和放热率曲线与实测值吻合较好。对缸内燃烧的温度分布计算表明:柴油燃烧滞燃期为2.5°CA左右,二甲醚为1.5°CA。柴油燃料着火始于喷雾前端两侧,在燃烧初期,其高温区分布在喷雾前端一侧,且在燃烧室内气流作用下沿垂直于喷雾方向扩散;二甲醚的着火点位于喷嘴附近,随喷雾的进行,其燃烧高温区从喷嘴附近一直延伸到喷雾前端,呈现狭长的高温带。在扩散燃烧后期,与柴油相比,二甲醚燃烧温度分布较均匀,且最高温度比柴油低。选用的9步NOx生成机理可较好地预测发动机实际运行中NOx排放水平。更多还原

【Abstract】 By using a CFD KIVA-3V model,the numerical results of combustion process and NOx emission simulation in a turbocharged diesel engine at the rated power were presented.Two fuels,diesel fuel and dimethyl ether(DME),were studied in order to gain an insight into the combustion characteristics of DME and diesel fuel.The results show that the calculated in-cylinder pressure and heat release rate are in good agreement with the measured results for both fuels.Distribution of temperature in the cylinder of the diesel engine and the DME engine shows that the ignition delay period of diesel fuel and DME is 2.5°CA and 1.5°CA respectively.At initial period of combustion,the high temperature region is located at one side of diesel fuel spray and propagates along the direction perpendicular to the spray under the effect of in-cylinder gas flow.For DME,the ignition position occurs near the nozzle and the high temperature distribution appears as a narrow belt along the DME spray from the nozzle to the tip of the spray.In comparison to diesel fuel,the in-cylinder temperature distribution of DME fuel is more even at later diffusion-combustion period,and the maximum local temperature of DME is lower than that of diesel fuel.The selected mechanism of NOx formation with 9 reactions can better predict NOx emission level of the engine.更多还原