The Simulation For Combustion Process Of DI Diesel Engine With Swirl Chamber

Pollution of diesel engine is recognized more and more important, and how to reduce the pollution has become a focus that all the researchers try to solve. The swirl-diesel has the characteristics of low pollution, low noise and good performance at high speed etc.. Compared with normal combustion engine, swirl-diesel still has disadvantages such as the high consumption rate of fuel and bad performance at engine start. If we can combine the advantages of swirl-diesel and normal diesel engine, it is very meaningful. The mean task of this thesis is trying to use the swirl of swirl-diesel into normal engine, so the combustion of normal engine can be improved.The key element to influence combustion is the mixture of air and fuel, and the quality of mixture lies on injection character, injection rule, the swirl inside the combustion chamber and chamber shape etc. The research method used in this thesis is software simulation with FIRE. The compression stroke, combustion stroke and expansion stroke have been simulated. The influence has been studied in this thesis which is injection timing, cylinder shape and injection duration on the mixture, combustion process, NO_X and particulate in diesel engine emissions. As for injection process, the movement of oil drops is analyzed by three-dimensional velocity vectorgraph. As for combustion process, the mixture distribution together with temperature distribution, velocity distribution, pressure distribution and emission distribution is analyzed to evaluate combustion quality.The results show: Comparison between the numerical simulation and the experimental results testifies the availability of numerical model, and numerical simulation is an effective tool to guide experiments; Compared between swirl-combustion engine and normal engine, swirl-combustion engine can make the fuel and air mix fast, and it also has a quicker extended combustion. From emission curves, we get the results that the swirl-engine's PM is lower, but NO_X is higher than the normal combustion engine's; Extending the injection duration is a good way to distribute premixed fuel, so it can reduce the pollution of NO_X effectively; Changing the injection direction is also a good way to reduce NO_X, because it can control the amount of fuel between swirl-cylinder and main-cylinder.