Research On Parameter Optimization And Flow Analysis Of Combustion System For Automotive Diesel Engine

The technologies in our country on emission control, especially for that with diesel engine, have fallen behind those advanced countries in Europe for about ten years. Since we joined the WTO, the EU-I and EU-II emission legislation have been carried out gradually. But in order to reach this aim from the old emission level which meets the ECE R15/04 legislation, it will be a difficult task depending on available technology level.The combustion process and emission characteristics in diesel engine are mainly depended on the mixture formation in cylinder. The gas flow and fuel spray status in combustion chamber are two important factors which affect the mixture formation in diesel cylinder. As a result, this dissertation presents the formation mechanism and characteristics of NOx and soot which are the main noxious emissions. At the same time, based on emission control technologies of diesel engine and practical condition of our country, this dissertation also utilizes the software FIRE provided by AVL Co. to simulate and analyze the flow field in combustion chambers for automotive DI diesel engines. Through the simulation and emission test, it can be concluded that this deep fowl DI combustion chamber with double swirls and central protuberance can be run in the wider speed range, and taken shorter time for mixture formation and combustion, which can accelerate the mixture formation and diffusion combustion. So this combustion chamber type can be used to control effectively and enforce the gases flow in the combustion chamber. As far as the heavy duty diesel engine is considered, because of its lower speed range and longer for mixture formation, the requirement for the gases flow in the combustion chamber is relatively not strict. So the shallow fowl DI combustion chamber with bottom protuberance is adopted to control effectively the flow intensity and made full use of the chamber space and it can be made to accelerate the diffusion combustion.Through the numerical simulation for this combustion chamber type, it can be shown, that the change of bottom may affect the flow distribution and the swirl intensity within the combustion chamber. Under the condition of Without change of the other dimensions and shapes, the reentrant shape with two stairways has no effect to the flow distribution and the swirl intensity in the combustion chamber, but it can improve the matching between the spray and combustion chamber which can affect engine's performance and emission. If the proper change of the squeeze surface is done, that can improve effectively the flow distribution and intensity without change of the swirl intensity existing. Through the comparison of test results, different flow distribution and intensity have also different emission characteristics. When flow intensity at the spray early stage is controlled, the NOx emission level can be decreased, the swirl intensity existing increased, the CO and HC emission also decreased. Although the swirl intensity existing is good, the flow distribution and swirl in the combustion chamber, especially when at heavy load operating condition the swirl intensity is larger, has bad effect to the CO and HC emission. It can be shown that when gas flow in the combustion chamber is organized, not only the swirl intensity existing is increased, but also the matching between the gas flow and its distribution is good, then the aim for control effectively the emission can be reached.In order to make full use of construction characteristics of this type combustion chamber, the optimized test for matching between the fuel supply (fuel injection) system and combustion chamber has been done. For the fuel supply system, the plunger diameter and its stroke are changed. For the constant fuel supply quantity, different plunger diameter and stroke can change the fuel supply history and its period. The comparison test results show that for this deep bowl open type combustion chamber, the change of plunger stroke has larger effect the diesel engine's performance. From the matching test fo...