天然气/柴油双燃料转子发动机燃烧过程的数值模拟

针对天然气/柴油双燃料转子发动机的缸内工作过程,基于FLUENT软件建立了耦合正庚烷简化机理的二维计算模型,并利用文献数据进行了验证。在此基础上,研究了纯柴油工况下喷射持续期对燃烧过程的影响,获得了较好的喷射持续期;并在该持续期下对天然气替代率对转子发动机燃烧过程的影响进行了研究。研究结果表明:保持当量比不变,喷射持续期的变化会对燃油浓度分布产生影响,从而影响燃烧过程;采用45℃A喷油持续期可以在保持较高缸内压力的同时减少污染物的生成。天然气替代率的提高会导致初期燃烧速度的减缓和后期燃烧速度的增大;随着天然气替代率的增大,燃烧初期同一偏心轴转角下的缸内压力和温度逐渐降低,燃烧后期则呈相反的趋势。采用50%天然气替代率可以在保持较高缸内压力的同时大大降低CO和Soot生成量,而NO生成量略有升高。

Numerical Simulation of Combustion Process of a Rotor Engine fueled with Natural Gas / Diesel blends

Based on the Fluent software, a two-dimensional calculation model of a natural gas / diesel dual fuel rotary engine coupled with a reduced reaction mechanism of n-heptane was established. The reliability of the model was verified by literature data. On the basis of this, the better injection duration of pure diesel was obtained, the effect of natural gas replacement rate on the combustion process of dual fuel rotary engine was studied under this injection duration. Maintaining the equivalent ratio, the results show that, when injection duration was 45°CA, high pressure and few contaminant can be obtained simultaneously, the increase of natural gas replacement rates will lead to the slow combustion rate of the initial combustion and the gradual increase of the later combustion rate. In the early stage of combustion, the pressure and temperature in the cylinder decrease gradually with the increase of natural gas substitution rate under the same eccentric shaft rotation angle while the post combustion process shows the opposite trend. When natural gas replacement rate was 50%, a high cylinder pressure can be maintained and at the same time the CO and Soot production were greatly reduced, while NO production increased slightly.