某重型柴油机怠速窜油问题研究

Reseach on Idle Oil Channeling of Heavy-duty Diesel

发动机活塞环同气缸套、活塞一同起到对燃气和机油的密封作用。但在大排量国六柴油机中,进气节流阀的应用使发动机缸内负压峰值增大,持续时间延长。当车辆长时间处于怠速或倒拖工况时,缸内负压可能超过活塞环的密封能力极限,从而使得曲轴箱内的机油持续被吸入气缸内,最终累积至排气管甚至后处理系统中。本次研究基于某13L重型柴油机售后排气歧管漏油的故障,通过精确测量,发现在进气节流阀最大80%的关度下,缸压负压峰值可达-30kP。从理论上分析了活塞组件的可能影响因素,利用流体仿真软件对不同单一变量下的反窜气水平进行了模拟,以初步验证理论分析。最终,在发动机台架上通过持续12h的怠速淌油测试以及100h的机油消耗测试确认了仿真措施的有效性。相关研究结果表明:第一道气环上梯角相对环槽由小21′改为大35′后,怠速机油消耗降低65%;第二道气环闭口间隙加大0.5mm,怠速机油消耗降低52%;增大气环弹力对怠速机油耗无明显影响;油环弹力增大50%时,怠速机油耗降低了26%。

Piston rings are critical parts of diesel engine,they seal the gas and oil together with piston and cylinder liner.But in heavy duty diesel,the intake throttle valve significantly increases the negative pressure in cylinder.When the vehicle is at idling or overrunning for a long time,the negative pressure in cylinder exceeds the sealing capacity of piston rings,oil in crankcase is pumped into the cylinder,accumulates to the exhaust pipe and even enters into post-treatment package.Based on exhaust manifold slobber failure of 13L heavy-duty diesel engine,the study measured idle cylinder pressure accurately and researched the influencing factors of idle oil comsuption.The fluid simulation software was used to compare the anti-channeling gas levels of different single variables to make a preliminary judgment on the theoretical analysis.Finally,the effectiveness of the simulation measures was confirmed by the slobber test for 12 hours and the oil consumption test for 100 hours.The study showed that:The upper angle of first ring changed from 7°to 7°56′,idle oil comsuption discreased 65%;The closed gap of second ring added 0.5mm,idle oil comsuption discreased 52%;The tangential force of compresstion ring did not have influence on idle oil comsuption;The tangential force of oil ring added 50%,idle oil comsuption discreased 26%.