【作者】 王海军；

【导师】 林学东；

【作者基本信息】 吉林大学 ， 动力机械及工程， 2007， 硕士

【摘要】 随着排放法规的日益严格,降低柴油机的排放已成为当务之急。本文针对GW2.5TC型高压共轨柴油机燃油喷射系统的特点,设计了两种不同凸台形状的深形缩口低排放型燃烧室(Ⅰ型和Ⅱ型),为了分析实际燃烧室内的气流运动特点及其规律,作为参考和对比分析,又建立了平底燃烧室模型Ⅲ。利用AVL公司提供的FIRE软件,对上述三种燃烧室结构进行了数值模拟计算。对Ⅱ型和Ⅲ型燃烧室缸内气体流动特点进行了分析,结果表明Ⅱ型燃烧室内部涡流保持性较强,有助于扩散燃烧,降低排放;对Ⅰ型和Ⅱ型燃烧室缸内气体流动特点进行了分析,得出了凸台形状对燃烧室内气体流动的影响;同时分析了Ⅰ型燃烧室在喷雾条件下缸内流场、湍流动能场、浓度场、温度场的变化规律,表明本文所设计的缩口低排放型燃烧室基本满足了喷雾与燃烧室内气流特性的匹配情况。通过台架试验,对比分析了不同燃烧室结构形状(Ⅰ型和Ⅱ型)对发动机性能的影响,从而选取了适合样机的燃烧室。更多还原

【Abstract】 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(typeⅠ、typeⅡ) 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 typeⅡcombustion 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 typeⅡcombustion 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 typeⅠc ombustion is a little better than the typeⅡ. The HC emission of the typeⅡcombustion chamber is far from better than the typeⅠas a result of the improving of the typeⅠ.更多还原