进气管结构对天然气发动机废气再循环率均匀性的影响

Effect of Intake Pipe Structure on Exhaust Gas Recirculation Uniformity of Natural Gas Engine

针对某国Ⅵ天然气发动机各缸燃烧一致性差异过大的问题,利用计算流体力学(CFD)软件STAR-CCM+对该发动机的进气管路开展废气再循环(exhaust gas recirculation,EGR)率均匀性分析,发现第1缸~第3缸的EGR率高于第4缸~第6缸,1200 r/min全负荷工况EGR率相对偏差为-29.9%~34.2%。分析表明,EGR的引出方式为第1缸~第3缸单侧取气,导致EGR进气入口存在较大波动,是造成各缸EGR率分配不均的主要原因。从降低管路内EGR废气波动的角度提出了两种进气管路优化方案,使EGR废气在进入稳压腔之前得到了充分混合,各缸EGR率均匀性得到明显提高,EGR率相对偏差在±5%以内。

In order to solve the issue of excessive difference in combustion consistence among the cylinders of a ChinaⅥnatural gas engine,an analysis of the exhaust gas recirculation(EGR)rate uniformity of the intake system was carried out by a computational fluid dynamics(CFD)software called STAR-CCM+.It was found that the EGR rates of from No.1 to No.3 cylinders were larger than those of from No.4 to No.6 cylinders,and the relative deviation of EGR rate at 1200 r/min with full load was from-29.9%to 34.2%.The analysis showed that there was a large fluctuation at the EGR inlet due to EGR being extracted only from No.1 to No.3 cylinders,which mainly caused the uneven distribution of EGR rate among the cylinders.Two optimizations of intake pipe were put forward to reduce the fluctuation of EGR in the intake pipe.By using the two kinds of optimized intake pipe,the recirculated exhaust gas is fully mixed before entering the intake manifold,which improves the uniformity of EGR rate in each cylinder obviously and brings the relative deviation of EGR rate to within±5%.