不同简化机理对高压直喷天然气船机燃烧和排放影响研究

Influence of different simplification mechanisms on combustion and emission characteristics of a high-pressure direct-injection natural gas marine engine

基于三维CFD仿真软件模拟了高压直喷天然气船机的燃烧过程,探讨了四种不同简化程度机理对燃烧和排放的影响规律。结果表明:四种机理均能很好的预测高压直喷天然气船机在不同喷射时刻下的缸压和放热率。四个机理预测的燃烧相位和最高爆发压力随喷射时刻提前或推迟变化趋势一致;预测的不同燃烧相位的温度、当量比和NOx分布存在较小差异。但35步机理和27步机理预测的碳烟排放比334步机理和250步机理高。整体上,受船机大尺度计算资源高限制,耦合简化的35步和27步机理的CFD模型预测的燃烧参数最大误差小于4.3%,预测的NO_(x)排放最大误差小于12.0%,能够满足船机工程开发需求。

The combustion process of a high-pressure direct-injection natural gas marine engine was simulated based on CFD software,then the effects of four different simplification mechanisms on combustion and emission characteristics were discussed.The results showed that the four mechanisms can well predict the in-cylinder pressures and heat release rates at different injection timings.The combustion phase and maximum burst pressure predicted by the four mechanisms show the same trend with the injection timing advanced or retarded.The predicted distributions of temperature,equivalence ratio,and NOxshow little difference.However,the predicted soot emissions of the 35-and 27-step mechanisms are higher than those of the 334-and 250-step mechanisms.Overall,limited by the large-scale and high computing resources of marine engines,the maximum relative error of the combustion parameters and NO_(x)emissions predicted by the CFD model coupled with simplified 35-and 27-step mechanisms is less than 4.3% and 12.0%,respectively.Therefore,the 35-and 27-step mechanisms can meet the requirement of the development of marine engines.