Study On The Effects Of The Injection Strategy On The Combustion And Emission Of A Diesel With Electrical Control System

Considering of the social responsibility of energy conservation and environmental protection, as well as the more and more strictly demands of the diesel engine performance from engine users and emission makers, the ICE workers have to make an effort on improving the engine's economy, dynamic property, exhaust emissions and noise level. The fuel injection system has direct and decisive influence on the combustion and emission of diesel engine. The traditional mechanical fuel supply system has already been no way to, satisfy the requirement of more stringent fuel consumption and emission legislation. For the past few years, it has been the research hot topic to improve performance of diesel engine combustion and emission through optimizing the fuel injection strategy at the Electronic Controlled High Pressure Common Rail Fuel Injection System.Adopting numerical simulation combined with bench test, the thesis studied the effect rule of the fuel injection strategy on diesel engine performance and emission. At first, mathematical modeling of the combustion chamber was established by using the commercial three-dimensional CFD (Computational Fluid Dynamics) numerical simulation software AVL Fire. The process of compression, fuel spray, combustion and expansion was simulated. Through comparing with experimental results, calculation models were proved to be reasonable. Based on this model, with numerical simulation of the different pilot injection timing, quantity and main injection timing, effects on diesel performance were analyzed. By comparing with experimental results, it showed that the simulation can effectively predict the emission.The results show that:1) The pilot injection can reduce the in-cylinder combustion noise obviously and improve the emission performance for diesel engines.2) With delaying the main injection timing, the duration of high temperature in cylinder becomes shorter; thereby the generation of NOx is decreasing. However because of the fuel combustion is delayed, the oxidation time of Soot is shortened; the emission of Soot is increasing.3) The changes of small pilot injection quantity don't have an obviously effect on the final NOx emission. When increasing the pilot injection quantity to 5 mm3, the emission of NOx becomes worse. When increasing the pilot injection quantity, the emission of Soot have a trend of increasing, what's more it will lead to worse combustion, when taken real operation it may increase fuel consumption.4) Fixed the main injection timing, when bring forward the pilot injection timing, the emission of NOx is decreasing, the emission of Soot has the same trend, but it does not change obviously.