Study On The Characteristics And Effects Of In-cylinder Flow On High Pressure Common Rail Diesel Engine Performances

Using diesel fuel has been a trend of modern automobile engine. Because of Diesel engine's advantages such as high thermal efficiency, easy to using turbo-charge, low fuel consumption, big torque, high reliability and long life-span, more and more auto-factories pay their attention to diesel engine. The more attention we pay to the crisis of energy and environment, the more economy and emission to automobile should be considered. People think much of the emission of diesel engine because its fuel economy is better than gasoline's engine. Although diesel engine's emission rate of HC and CO is excelled gasoline, its'NOx emission is as much as the latter. Furthermore, the PM emission of diesel is dozens times than that of gasoline engine. So, how to reduce the emission of NOx and PM of diesel is a problem that we should urgently figure out.In order to improve the fuel consumption and emission characteristics, the parameters of combustion need to be optimized. When improving the combustion system, the first step is usually to improve the combustion chamber shape. In the dissertation, according to the performance of the GW2.5TC HPCR diesel engine, I designed two kinds of reentrant lower-emission combustion chamber(typeâ… ,typeâ…¡) based on the combustion chamber of the GW2.8T HPCR diesel engine. In order to analyze the flow characteristic of the mixture gas, I have also designed a kinds of combustion chamber whose bottom is flat. After matching with supercharger, the performance of the diesel engine will meet the demand. Aiming at the shortcoming of the engine that its HC emission is a little high, the typeâ…¡combustion chamber was designed. The purpose is to study how to reduce the HC emission.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 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 reentrant low-emission DI combustion chamber with doubleswirls 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. Consequently, the quality of mixture formation can be improved.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. 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. Through the analyse of distributing of concentration, velocity, TKE and temperature in the computational area, it can be concluded that the distribution of the flow has an importance effect on the mixture gas. The combustion chamber which are designed in my dissertation meet the demand. 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 the two types of combustion chamber has been done. The two types of reentrant combustion chamber were designed according to the performance of the HPCR 2.5TC diesel engine and the experience. The typeâ…¡combustion chamber is designed aiming at the shortcoming of the diesel engine that its HC emission is high. The results show that the distinction between these two combustion chamber's performance is tiny, The engine performance will be demanded if the supercharge is optimized; As far as the emission characteristics, the PM,CO,NOx emission of the typeâ… c ombustion is a little better than the typeâ…¡. The HC emission of the typeâ…¡combustion chamber is far from better than the typeâ… as a result of the improving of the typeâ… .