Application Research On DOC+POC Matching Mechanical-line Pump Diesel Engine

Electronic fuel injection pumps have lots of advantages, such as stable running, fast response, high precision, compact structure, convenient maintenance, and so on. However, the traditional mechanical fuel injection pumps still have market competitiveness in diesel engine field because of low cost, simple injection control, and other edge. Therefore, to work on emission control about diesel engines which are equipped with mechanical fuel injection pumps would be very important for the purpose of energy saving and emission reduction of vehicles. This paper mainly discusses emission upgrade technical routes of the YC6L engine with inline fuel injection pumps.Diesel engine discharge pollutants include PM, NOx, HC, CO, and so on. Emission control regulations have governed strict limit values, especially PM and NOx. Due to the existence of "trade-off" relationship between PM and NOx emission control, we couldn’t only use purify in-engine technique to reduce PM and NOx emission effectively at the same time. Consequently, this article chooses after treatment system as solution to upgrade YC6L diesel engine emission.This paper firstly to expound the harmfulness, formation mechanism, and influence factors of diesel engine discharge pollutants; after that, mainly to introduce the after treatment technology, such as DOC/DPF/POC/SCR, to research their effecting mechanism, abilities and restricted factors. Further, these fundamental theories would offer help for the selection of catalyst. Considering the economic cost and the emission regulations, the finally determined technical route for YC6L diesel engine emission meeting Stage IV standard is DOC&POC&SCR combined-type after-treatment system. Emission upgrading from Stage III to IV standard requires PM conversion efficiency could exceed80%, so PM emission control is the key factor to attain to Stage IV standard for diesel engine. Further, this paper would put more emphasis on reasonable evaluation of the selection of POC catalyst, which is assembly in combined after treatment system using for purifying PM.In order to evaluate the rationality of the selection of the POC catalyst, diesel engine test should be carried out for inspection. Therefore, the thrust stand should be set up, and test subject, control device, POC catalyst, emission test equipment would be introduced. To analyze the data of the bench test, influence law of PM conversion efficiency bound by fuel oil in sulfur and soot load on POC catalyst, this paper would obtain a series of conclusions as follows:(a) The combined after treatment system could result in power loss;(b) With the POC inlet temperature and GHSV increase, the PM conversion efficiency would present the curve of hump;(c) In the low temperature conditions, the PM emission is small, even if long time working on these points, the soot load on POC catalyst is also low, and the rate of working conditions changing on real vehicle is so frequent that the POC catalyst would regenerate during high temperature conditions;(d) When engine load increase radically, the "soot puffing" phenomenon is very obvious, therefore, we need to limit the rise rate of engine load to weaken the "soot puffing" phenomenon and reduce PM emission.Generally speaking, for many kinds of diesel engine, which are equipped with mechanical fuel injection pumps, we could select the combined after treatment system as solution to upgrade engine emission.