Effects Of Fuel Injection Strategy On Combustion And Emission On Heavy Duty Common Rail Diesel Engine And Its Optimization

Dieselization is a great trend in engines. However under the pressure of energy crisis and environment pollution, diesel engine as well has to face problems in several aspects. High-pressure common rail fuel injection system is a reasonable way to improve efficiency, emmision and economy of diesel engines.High pressure fuel injection system can improve the effect of pulverization and help the fuel mix with air sufficiently to form the homogeneous mixture, thus improve the performance of combustion. So the technology of high pressure fuel injection system is widely applied in the heavy diesel engine. As the fuel injection pressure of common rail fuel injection system is not influenced by the speed of engine, and the parameters of common rail system could also be controlled freely. Furthermore,with the common rail fuel injection system the cylinder head and the body of the diesel engine don't need to be changed too much. Thus the common rail fuel injection system is a very promising technology.Injection characteristics have great influences on the process of combustion. The future fuel injection system should be able to hold the higher injection pressure in the whole operation range, of which the injection pressure and timing should also be controlled independently. Injection characteristics can be controlled and the drive loss caused by the high pressure injection system can also be reduced. Electronic controlled variable pilot injection pump, single-plunger fuel injection pump and common rail fuel injection system will be the very important measures to satisfy the future emission laws and regulations.The high pressure fuel pump of the common rail injection system delivers the high pressure fuel continually to the common rail. With the common rail fuel pressure controlled accurately, the pressure of the high-pressure fuel pipes is independent of the speed of the engine. Thus the influence of engine speed on the fuel-feed pressure can be reduced remarkablely. Injection quantity and timing of the injector can be controlled to achieve the better pulverization and finally the optimal combustion, the adequate power and the lowest exhaust emission.The diesel engine used in this paper's experimentations was equipped with Bosch company's second generation high-pressure common rail fuel injection system. The control and calibration software was INCA which was a online calibration software. The main contents in this paper are as follows: Firstly, introduced the experimental object CA6DL2-35E3 which was a electronic controlled turbo-charging and inter-cooling high-pressure common rail diesel engine, the installation of the test bench and the design of the test and control system. Then analysed the control methods of the parameters of the high-pressure fuel injection system such as the common rail pressure, injection advance angle, post injection timing and post injection mount and analysed profoundly the relationship of the parameters and the influence factors of their controlling maps, and confirmed the calibration flow of the engine and the calibration method of the maps. Thirdly, changed the common rail pressure, injection advance angle, post injection timing and post injection mount respectively with keeping other parameters unaltered and analysed the parameter's influence to the combustion process, economy and emission of the engine. Finally, optimized the injection system and analysed contrastively the emissions before and after the optimization.The experiments proved that the optimization of the parameters of the injection system improved the economy and the emission of the diesel engine: with the increase of common rail pressure, NOx took on an increasing trend, PM took on a decreasing trend, HC decreased with the increase of the rail pressure with a maximum extent of 20%, CO decreased greatly with a maximum extent of 70%. In conditon of postponing injection, the maximum increaseed extent of BSFC was 15%, the changing extent of NOx was 50% more or less, CO changed more than 100%, HC increased 15% more or less.With the increase of post injection mount, NOx decreased 50%, PM deceased 80%, CO decreased a little at first but then took on an increasing trend with maximum extent of 25%, HC increased with the increase of post injection mount with a maximum extent of 70%. With the postpone of post injection, generally speaking NOx took on a decreasing trend, PM decreased with a maximum of 70%, HC increased with the decrease of post injection timing with a maximum extent of 100%, The maximum increasing extent of HC was 140%.