点燃型预燃室在大缸径甲醇发动机上的应用

Application of Ignition Pre-Chamber in a Large-Bore Methanol Engine

通过计算流体动力学数值模拟,探索点燃型预燃室在大缸径(320 mm)甲醇发动机上的应用效果,计算了过量空气系数和点火正时对燃烧和性能的影响。结果表明,点燃型预燃室发动机的燃烧放热过程先缓后急,热效率较高,NO_(x)排放很低,SO_(x)排放为零,不经后处理即可满足国际海事组织TierⅢ排放法规。随着缸内过量空气系数的增加,缸内压力、压力升高率、声响强度和NO_(x)排放均显著降低,指示热效率先升后降,在过量空气系数为2.4时达到最高值49.2%;随着点火正时的延迟,缸内压力、压力升高率、声响强度、指示热效率逐渐下降,NO_(x)排放先减后增。基于计算结果,提出了一种燃烧控制策略:在平均有效压力低于1.8 MPa时控制缸内过量空气系数为2.4并匹配较早的点火正时,在平均有效压力高于1.8 MPa时控制过量空气系数为2.1并匹配较晚的点火正时。采用该策略可使部分负荷热效率最佳,且整机具有较高的动力性。

Based on numerical simulations of computational fluid dynamics(CFD),the effects of ignition pre-chamber on a large-bore(320 mm)methanol engine were investigated,and the influences of excess air ratio and ignition timing on combustion and performance were simulated.Results show that,with the ignition pre-chamber,the combustion processes are characterized by initially slow and then rapid heat release rates,resulting in high thermal efficiencies,low NO_(x)emissions and zero SO_(x)emission,which could meet the International Maritime Organization(IMO)TierⅢemission regulations without aftertreatment.Furthermore,with the increase of the excess air ratio,the cylinder pressure,the pressure rise rate,the ringing intensity(RI)and the NO_(x)emissions are significantly reduced,while the indicated thermal efficiency initially rises and then falls,reaching a peak value of 49.2%at the excess air ratio of 2.4.With the retarding of the ignition timing,the cylinder pressure,the pressure rise rate,the RI and the indicated thermal efficiency are reduced,while the NO_(x)emissions initially fall and then rise.Based on the numerical results,a combustion control strategy is proposed.When the brake mean effective pressure(BMEP)is lower than 1.8 MPa,the excess air ratio should be 2.4 with an earlier ignition timing;when the BMEP is higher than 1.8 MPa,the excess air ratio should be 2.1 with a later ignition timing.With this strategy,the engine can obtain high power density and optimum thermal efficiency at partial loads.