运行参数对微型内燃机微燃烧特性影响机理分析

微型内燃机微燃烧过程对当量比和转速变化非常敏感，采用层流有限速率模型和甲醇氧化反应机理对其预混层流微燃烧过程开展仿真研究，探讨当量比和转速对微燃烧特性的影响规律及临界运行参数。在此基础上，提出采用热着火理论和化学反应动力学理论探索当量比对微燃烧特性的影响机理。结果表明仿真与实验比较吻合。当量比从0.6增加到1.1时，燃烧速率增加，压力和温度增加，压力最高值增加约1.5E+6 Pa，温度最大值增加约1 300 K，此后随当量比增加，燃烧速率减小，压力和温度减小。研究还进一步揭示了当量比影响微燃烧特性的机理: 稀燃区当量比主要通过温度变化来影响微燃烧特性，随当量比增加，燃料浓度增加，燃烧释放的总热量增加，所以温度和压力增加，燃烧速率增加；浓燃区当量比主要通过氧气量变化来影响微燃烧特性，当量比越大，氧气量越不足，基元反应速率越小，所以燃烧速率越小，温度和压力越低。转速越高，燃烧时间越短，燃烧越不充分，所以温度、压力越低。受微燃烧相对热损大、驻留时间短的特征影响，微型发动机实现完全燃烧的运行区域较窄，其实现完全燃烧的稀燃极限约0.9，最高转速约6 000 r/min。这在设计微型内燃机时值得关注。

Effect mechanism analysis of operation parameters on micro combustion characteristics in micro IC engines

Micro combustion process of micro IC engine is very sensitive to changes of equivalent ratio and speed. The laminar flow finite rate model and methanol chemical reaction mechanism is adopted to simulation its premixed laminar combustion process. And then, the influence law of equivalent ratio and speed on micro combustion characteristic is explored, and the critical operation parameters are investigated. Finally, the thermal ignition theory and chemical reaction kinetics theory is adopted to explore the influence of equivalent ratio on micro combustion characteristic mechanism. The results show that simulation results agree well with experiment. When equivalent ratio increases from 0.6 to 1.1, the combustion rate, the pressure and the temperature increase, pressure peak increases by about 1.5E+6 Pa and the maximum temperature increases by about 1 300 K. Since then, with the increase of ratio equivalent, the combustion rate, the pressure and the temperature also reduce. Moreover, the research reveals the mechanism that equivalent ratio affects micro combustion characteristic. In dilute zone, equivalent ratio mainly affects micro combustion performance by temperature changes. As equivalent ratio increases, fuel concentration and released heat increase, thus the temperature and the pressure increase, and then combustion ratio increases. In thick zone, equivalent ratio mainly affects micro combustion performance by oxygen changes. As equivalent ratio decreases, oxygen volume and reaction rate decrease, thus combustion ratio decreases, and then the temperature and the pressure decrease. When the speed lifts, the time for combustion is shortened, thus the complete combustion level reduces and the temperature and the pressure drop. Because of relatively large heat loss and short residence time of micro combustion, the complete combustion operation area of micro engine is narrow. The lean burn limit to realize complete combustion is about 0.9 in our experiments, and the highest speed is about 6 000 r/min. It is worth to being paid attention to when the micro IC engine is designed.