基于燃烧室与增压器匹配的柴油机热效率优化设计及仿真研究

Optimization Design and Numerical Simulation of Combustion Chamber and Turbocharger Matching for Improving Thermal Efficiency of a Diesel Engine

以某重型柴油机为研究对象,采用仿真计算的方法探究了基于缸内燃烧系统和空气系统优化使发动机最低油耗区间匹配不同使用工况,提出满足发动机不同应用场景需求的匹配方案。研究结果表明:采用压缩比为19.5的燃烧室,缸内混合气过稀区减少,燃烧放热速率加快,热效率提高;通过合理匹配增压器和燃烧室可以实现柴油机最低油耗区间与目标工况区间的匹配。以优化低转速中低负荷工况油耗为目标,采用压缩比为19.5的燃烧室,同时采用较小的涡轮当量流通截面积,可以使最低油耗区匹配低转速中低负荷工况,低转速中负荷油耗改善3.1%。以优化中转速中高负荷油耗为目标,采用压缩比为18.5的燃烧室,结合增压器的优化匹配,可以使最低油耗区匹配中转速中高负荷工况,中转速中负荷油耗改善1.6%。以优化高转速高负荷油耗为目标,通过提高最高燃烧压力,采用压缩比为21.5的燃烧室,同时采用较大的涡轮当量流通截面积,高转速高负荷油耗可改善4.2%。

Based on a heavy-duty diesel engine,a numerical simulation study of the scheme which could move the minimum fuel consumption range to different conditions by matching different combustion systems was carried out.Results show that when the compression ratio was 19.5,the distribution of the lean mixture in the cylinder was reduced,and the heat release rate was faster,resulting in a higher thermal efficiency.The minimum brake specific fuel consumption(BSFC)range could be moved to various target conditions by matching turbocharger and combustion chamber appropriately.When the compression ratio was increased to 19.5,combined with turbocharger configurations optimized at low speed,the minimum BSFC range could be moved to low speed condition,with BSFC upmost reduction of 3.1%.When the compression ratio was increased to 18.5,together with turbocharger optimization,the minimum BSFC range could be moved to medium speed condition,with BSFC reduction of 1.6%.Similar approach was applied at high speed and high load with elevated peak in-cylinder pressure limit,within which a relatively larger turbine was adopted and the compression ratio was increased to 21.5,and the BSFC at high speed and high load could be reduced by 4.2%.