曲轴箱通风口海拔模拟条件对柴油机运行的影响

Influence of Altitude-Simulated Condition at Crankcase Vent on Diesel Engine Operation

针对柴油机进排气高原环境模拟装置在应用中存在的问题,基于活塞、活塞环、气缸套形成的几何密封结构,确定了缸内气体向曲轴箱流动形成的气室,进一步构建环间气体窜出流量的数学模型,运用迭代计算方法推演计算了各个气室气体压力和气体流量的变化,分析了曲轴箱通风口与进排气管路模拟海拔不一致时活塞窜气影响和增压器轴系润滑密封问题,最后进行试验验证。研究结果表明,海拔4 500 m时曲轴箱通风口处于相同海拔环境条件,曲轴箱通风口窜出废气流量要比处于试验室环境条件时窜出气体流量大,增加0.4 L/min。此外,曲轴箱通风口处于试验室环境条件时,压气机背盘两侧气体压力差异会使间隙空间形成很大的负压,导致润滑增压器轴承的机油窜入进气管路。

For the application problem of intake and exhaust plateau environment simulation device, the gas cavities from cylinder to crankcase were determined, and the numerical model of blowby gas flow through the gap was built according to the geometrical sealing structure of piston, piston ring and cylinder liner. Then the gas pressure and gas volume flow variation of each gas cavity were calculated by using the iterative method. The blowby influence and turbocharger shaft sealing were further analyzed under the altitude-simulated condition of the intake and exhaust pipes that was different from that of the crankcase vent. The discussion and verification were finally carried out. The results show that the blowby gas flow will increase by 0.4 L/min when the 4 500 m altitude-simulated condition of crankcase vent is conducted. Besides, the difference of gas pressures on both sides of compressor disk will cause a large negative pressure in the gap so that the lube oil for turbocharger bearing enters the intake pipe when crankcase vent is directly open to the atmosphere.