低压EGR与水冷式中冷器冷凝对发动机性能影响的试验研究

Experimental Study on the Effects of the Low Pressure EGR and WCAC Condensation on Engine Performance

外部冷却、低压EGR技术由于可降低泵气损失、抑制燃烧速率、降低爆震倾向和降低排气温度,对改善发动机燃油经济性和降低排放具有非常好的效果,是近年来发展比较迅速的节能减排技术,但EGR废气对压气机叶片的腐蚀是最大挑战。中冷器内部因EGR废气与冷却水之间存在温差,容易在中冷器翅片处产生冷凝水。当中冷后温度低于25℃时,发动机进气道口出现大量冷凝水并进入到气缸内,严重影响燃烧稳定性,发动机甚至出现排气温度升高、产生失火等现象。WCAC冷凝对发动机性能影响的试验结果表明,2缸出现大量冷凝水,COV(循环变动系数)波动较大;1缸与3缸只有少量冷凝水,COV波动较小。从安装在各缸的摄像头可以看到,2缸的冷凝水问题最严重,1缸与3缸情况较好。就冷凝水对压气机叶片产生腐蚀以及对发动机性能产生不利影响、减少冷凝出现的措施、涂层增加压气机叶片使用寿命进行了试验研究。

External cooling and low-pressure EGR technology can reduce pump gas loss,inhibit combustion rate,decrease knock tendency and reduce exhaust temperature,which has a very good effect on improving engine fuel economy and reducing emissions.It is a relatively rapid development of energy saving and emission reduction technology in recent years,but EGR exhaust gas on compressor blade corrosion is the biggest challenge.Due to the temperature difference between EGR exhaust gas and cooling water inside the intercooler,condensation is easy to be generated at the fin of the intercooler.When the temperature after the middle cooling is lower than 25℃,a large amount of condensed water appears at the intake ports and enters the cylinder,seriously affecting the combustion stability,and the engine even appears the exhaust temperature rising,mis-fire etc.The test results of the effect of WCAC condensation on engine performance show that there is a large amount of condensation in 2 cylinders and COV(cycle variation coefficient)fluctuates greatly.There is only a small amount of condensation in cylinder 1 and cylinder 3,and the COV fluctuation is small.As can be seen from the camera installed in each cylinder,the condensation problem of cylinder 2 is the most serious,while the situation of cylinder 1 and 3 is better.The condensate corrosion on compressor blades and the adverse effect on engine performance,the measures to reduce condensation and the coating to increase the life time of compressor blades are studied experimentally.