可变二级增压柴油机变海拔工作特性数值模拟

Numerical Simulation on Performance of Diesel Engine Equipped with Regulated Two Stage Turbocharging Systems at Different Altitudes

以两级增压共轨重型柴油机为研究机型,采用GT-Power构建了其一维热力学仿真模型,对比可变二级增压(RTST)柴油机随高压级可变截面涡轮增压器(VGT)在不同叶片开度(20%~100%,)及不同海拔(0~4,km)下的工作特性.结果表明:不同转速工况下,空燃比和泵气损失随VGT叶片开度和海拔高度增加而降低.不同海拔下,随VGT叶片开度增大,低速时转矩与有效热效率先升高、后降低,高速时显著增大.随叶片开度和海拔增加,NO_x排放降低,soot排放大幅升高.海拔为4,km时,叶片开度从20%,增至100%,,低、高速工况的转矩和有效热效率均分别增加7.5%,和39.2%,,NO_x排放分别降低38%,和24%,;海拔为2,km时,不同转速工况下柴油机匹配RTST均能实现较高的EGR率(超过60%,).VGT叶片开度减小,EGR率快速增大,转矩及有效热效率降低,有效燃油消耗率(BSFC)逐渐增加,NO_x排放快速降低,soot排放先升高后降低.在EGR率约为35%,时,RTST柴油机综合性能达到最佳.

Based on the calibrated one-dimensional thermodynamic simulation model constructed by GT-power, the comparative study on performance of a common-rail heavy-duty diesel engine equipped with regulated two stage tur- bocharging （RTST） systems was conducted at different altitudes （0-4 km）. Results show that, at different speed con- ditions, the air-fuel ratio and pumping loss of the engine decrease with the increase of the VGT blade opening and the altitude. At different altitudes, the torque and the break thermal efficiency increase with the increase of VGT opening under low speed, and increase significantly under high speed. With the increase of blade opening and altitude, NOx decreases and soot increases rapidly. At altitude of 4 km, both the torque and the brake thermal efficiency under low and high speed working conditions increase by 7.5% and 39.2% respectively, and the specific emission of NOxde- creases by 38% and 24% respectively when the VGT blade opening increases from 20% to 100%. At different speed conditions, the diesel engine equipped with RTST can achieve a higher EGR rate （more than 60% ）at altitude of 2 kin. With the decrease of the blade opening, the EGR rate increases rapidly and the torque and the brake thermal efficiency decrease. While the BSFC increases, the specific NOx emission decreases rapidly, and the specific soot emission increases first and then decreases. When EGR rate is within 35%, the comprehensive performance of the RTST diesel engine reaches the best point.