喷水对天然气发动机性能影响的数值模拟

Numerical Simulation of Impacts of Water Injection on Performance of Natural Gas Engines

摘要:

通过数值模拟的方法研究喷水技术对重型天然气发动机燃烧和排放特性的影响.结果表明，喷水对天然气的低温反应阶段无显著影响，但是在高温反应阶段，OH自由基的生成速率被抑制，使得没有足够的氧化剂氧化CO，燃烧持续期延长，反应温度降低.随着喷水质量的增加，火焰传播速度减慢，致使燃料放热速率减缓，燃烧的持续期延长，最高温度降低，相位推迟.喷水位置距离燃烧室越近，水雾蒸发吸热降低燃烧室温度的作用越明显，这有利于增加进气过程的缸内充量密度.此外，喷水可以显著降低发动机的热负荷，抑制燃烧室内氮氧化物的生成，从而为天然气发动机的当量比燃烧提供可能性.

Abstract:

This paper focused on the effects of water injection on combustion and emission characteristics in heavyduty natural gas engines by numerical methods. The results show that water injection has no significant effects on the stage of low-temperature reactions, but the generation rate of OH radicals is limited in the stage of high-temperature reactions. Therefore, there is not enough oxidant to oxidize CO. The combustion duration is extended, and the temperature during the combustion is reduced. Moreover, the flame propagation speed and fuel heat released rate slow down with the increase of water injection quantity. The combustion duration and phase are delayed, and the maximum temperature decreases with the water quantity increasing. Besides, the spray position closer to the combustion chamber contributes to the effect of water evaporation on reducing the temperature in the combustion chamber, which is beneficial to increasing the charging density in the intake stroke. Water injection can significantly limit the thermal load of engines and the formation of nitrogen oxides in the combustion chamber, thereby providing the possibility of equivalence ratio combustion in natural gas engines.