Study on the ignition and the combustion control of combustible mixtures in the spherical confined vessel

为了建立柴油机燃用二甲醚循环的模拟模型，在实验室自制的球形燃烧室上进行了基础性试验。直径为200 mm的容器配备了多点点火系统，通过改变燃烧持续时间和火焰传播模式来改变容器内的热释放速率。由于热损失主要是由火焰对容器壁面的干扰引起的，因此热释放速率直接影响着废气的排放，本文对不同当量比和不同放热模式的二甲醚-空气混合物进行了预混燃烧试验。测量了氮氧化物（NOx）的排放量，并与多区燃烧模型的计算结果进行了比较。在此基础上，利用改进的三区燃烧模型对柴油机直喷二甲醚的燃烧过程进行了模拟分析。用改进后的模拟模型对实际四冲程柴油机的示功图和氮氧化物排放进行了计算。试验结果表明，该方法能够较好地预测放热率变化时NOx排放量的变化。在不同速率下的模拟试验中，放热过程中高温持续时间越长，NOx排放量越高。模拟结果表明，控制放热率可以改善发动机的排放特性。

To develop a simulation model for a Diesel engine cycle using DME fuel, the fundamental tests were carried out with the spherical combustion vessel which was made experimentally. The vessel of 200mm diameter equipped with the multipoint ignition system which can vary the heat release rate in a vessel through altering a burning duration and a flame propagation pattern. Since the heat loss is primarily based on the flame-interference with vessel wall, the heat release rate directly affects the exhaust emission.The premixed combustion tests with a di-methyl ether-air mixture were carried out for different equivalence ratios and heat release patterns. The emissions of oxides of nitrogen(NOx) were measured and compared with the calculated results from the multi-zone combustion model. The results showed that the model was valid for estimation of NOx.On the basis of this model, diesel combustion processes with a direct injection of DME were analyzed by making use of the modified simulation model with 3-zone combustion model. The indicated pressure diagrams and the emissions of oxides of nitrogen from the practical 4 cycle diesel engine were used for the calculation with the modified simulation model. The test results have shown to be proper for estimating the change of NOx emission when the heat release rate is changed. In the simulation by inspecting with the various rates, the longer duration of high temperature in the heat release process resulted in the higher NOx emission. From the results of simulation, it has been shown to be able to improve the exhaust emission characteristics of the engine by controlling the heat release rate.