利用FIRE软件仿真分析了将压缩天然气(CNG)燃料按不同喷射方式直接喷入气缸时对微观物理场及火焰传播机理和NO生成规律的影响.结果表明:CNG燃料的混合气形成机理取决于其喷入气缸后相对缸内空气的分离速度,喷射时刻通过控制喷射过程中向气缸喷入的动能来抑制天然气相对空气的分离速度,从而决定浓度场的分布;当早期喷射时缸内易形成上浓下稀的浓度分布,晚喷射时则易形成下浓上稀的混合气;NO的生成速率取决于当时当地的一定的混合气浓度和温度,当当量比或温度偏离某一范围时NO生成速率几乎为零;而NO的最终生成量取决于NO的生成速率、生成区域面积的大小以及生成反应持续时间.%The effects of different direct injection methods of compressed natural gas (CNG) fuel into the cylinder on the microscopic physical fields , the flame propagation mechanisms and the NO formation mechanism were simulated and analyzed using software FIRE .The results show that ,after injection the formation mechanism of CNG fuel mixture depends on its separation speed relative to the air in the cylinder ,and the separation speed of CNG is controlled effectively by the injection timing according to the kinetic energy provided by gas fuel during the injection , which determines the distribution of concentration fields .During the compression stroke , the concentration distribution rises from the bottom to the top if the fuel was injected early and vice versa .The NO formation rate depends on the concentration and temperature of local mixture .The NO formation rate is almost 0 regardless of equivalence ratio when temperature is lower than 2000 K .The amount of NO production depends on the NO reaction rate ,the size of production area and the reaction duration .
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