Simulation Study On Combustion And Emission Process Of High Proportion Of DME-Diesel Mixed Fuel

As a clean alternative fuel of vechiles, DME has been increasingly applied in compression-ignition engines. This paper analyses the characteristics of DME as the fuel of compression-ignition engines, sums up the current research of DME at home and abroad, and makes a research on the in-cylinder turbulence flow and the current research of combustion simulation to an extent. The combustion of engine is an important factor which relates to the power and economic as well as emission performance. Limited to the experiment condition, it is impossible to study the relation between the fuel distribution and the emission, and also the actual condition of in-cylinder combustion. But with computer technology and related knowledge of fluid, it is possible to study the combustion process through numerical simulation.By using the FIRE software, this paper sets up the combustion chamber model of 4100 diesel engine and carries on the grid partition. Also, the paper simulates the combustion and emission from the inlet valve closed to the outlet valve opened. Through the comparison between the simulation results and the results from the combustion analyzer in the test stand, the paper verifies the correctness of the model. What's more, this paper makes a research on the 3D results such as velocity distribution, temperature field, emission field, fuel concentration, and the 2D results such as mean pressure, mean temperature, emission mass fraction and so on. The results show that NOx growth will come to a"freezing period"when it comes to a certain temperature during the expansion stroke, while soot growth is growing first and oxygenated later. The results also appear that the fuel spray influences the velocity distribution.Based on this, this paper selects three high proportional DME-diesel fuels such as D65, D75 and D85, and makes a research on the rule of diesel and the three kinds of fuels in the in-cylinder mean pressure, mean temperature, fuel mass fraction and emission mass fraction. What's more, this paper makes a comparison of combustion process, temperature distribution and emission distribution. The result shows that the maximum pressure of high proportion DME-diesel fuel is lower than diesel's, but maximum temperature and accumulated heat release is close to each other while higher than diesel's. It appears that high proportion DME-diesel fuel can reduce the mechanical load in cylinder with high efficiency. With the increase of the proportion of DME, NOx grows later and NOx mass fraction is lower. Besides, the mass fractions of soot of three kinds of mixed fuels are far below diesel's, D85's is the lowest.This paper studies the influence to high proportion DME-diesel fuel through the changes of injection advance angle and injection duration, and provides a theory basis for the high proportional DME-diesel fuel. The results show that mean pressure, mean temperature and accumulated heat release will increase with advance of injection angle, but at the same time NOx and soot mass fraction will increase too; the extended injection duration will result in mean pressure lower too much.