增压方式对柴油机高原环境下工作特性影响的数值模拟

Numerical Simulation of Influence of Turbocharging Modes on Working Characteristics of Diesel Engine at Plateau

以一台高压共轨重型柴油机为研究机型,构建了一维热力学模型,首先对比研究了单级增压(single-stage turbocharger,1TC)和二级增压(two-stage turbocharger,2TC)对柴油机变海拔条件下工作特性的影响;然后将2TC的高压级更换为可变截面涡轮增压器,在4 km海拔条件下,分析了叶片开度对柴油机性能的影响。结果表明:相较于1TC,2TC可进一步提高柴油机对海拔变化的适应性,特别是在低转速工况下效果更加明显。低转速工况时,可变二级增压柴油机叶片开度在40%~70%转矩最大,有效热效率最高,有效燃油消耗率最低;随着转速升高,增大叶片开度可降低排气背压,减少缸内残余废气,提高增压器效率,NO x排放减少,有效燃油消耗率降低;低转速时传热损失率随叶片开度增加先减小后增加,中高转速时传热损失随叶片开度增大而下降。

Based on a high-pressure common rail heavy-duty diesel engine,a one-dimensional thermodynamic simulation model was built.Firstly,the effects of single-stage turbocharger(1TC)and two-stage turbocharger(2TC)on the operational characteristics of diesel engine under variable altitudes were compared.Afterward,the high-pressure stage of 2TC was replaced with a variable geometry turbocharger to investigate the effects of the blade opening on the performance of the diesel engine at an altitude of 4 km.The results show that compared with 1TC,2TC can further improve the adaptability of diesel engine to altitude changes,especially in low speed conditions.In low speed conditions,the regulated two stage turbocharger system diesel engine has a maximum torque,highest effective thermal efficiency and lowest break specific fuel consumption(BSFC)when the blade opening were between 40%and 70%.As the speed increases,enlarging the blade opening can reduce the exhaust back pressure and residual exhaust gas in the cylinders,increase the efficiency of the turbocharger,and decrease NO x emissions and BSFC.At low speed conditions,the heat transfer loss rate decreases firstly and then increases with the increase of the blade opening.At medium and high speed conditions,the heat transfer loss rate decreases with the increase of the blade opening.