Study On The Combustion Process Of Methanol In A Direct Injection Compression Ignition Engine

In a variety of alternative fuels for internal combustion engine, methanol is found to be the most prospective fuel due to its high octane value, fine antiknock property, fast flame propagation velocity and close to zero emissions of particulate matter. The thermal efficiency of methanol in compression ignition engine is high, but due to its low cetane value, the high latent heat of vaporization and high combustion temperature, resulting in methanol in compression ignition engine can’t be ignited by compression ignition combustion mode, so we need to take some supporting measures. The supporting measures for methanol combustion basically have two methods:(1) increasing the intake temperature, making the cylinder compressed temperature near top death center to reaching the auto-ignition temperature of methanol;(2) changing methanol combustion ignition mode from compression combustion ignition mode to the spark plug ignition mode. In this paper, as for the characteristics of methanol we take the first measure. Starting from the increase of the intake air temperature, with a four cylinder compression ignition engine as the research object, I use the software to establish the model of the cylinder internal combustion model of the compression combustion direct-injection engine, through the experimental value of the existing diesel fuel, the model simulation results are verified and validated. Based on the validation of the model, the characteristics of the engine fueled with methanol fuel were studied, The simulation calculation of different inlet temperature,injection timing and injection hole diameter is carried out to realize the analysis of methanol combustion process, the following words are the main research contents:(1) A mathematical model for the establishment of a pressure ignition direct injection engine;(2) The physical geometry model of the engine is established;(3) The boundary conditions and the model parameters are set up to verify the validity of the model;(4) Based on the validation of the model, the diesel engine is replaced by the methanol fuel;(5) The model is simulated by variable parameters, including inlet temperature,injection timing, diameter of the nozzle, and the influence of these parameters on the combustion of methanol.Analysis results show that:(1) With the increase of inlet air temperature, the ignition time of methanol is advanced, the combustion delay period is shortened, and the temperature curve of the cylinder increases higher. The inlet temperature is too low, which will result the combustion of methanol can’t reach the auto-ignition temperature of methanol, and the inlet temperature is too high, which will lead to the burning of methanol in advance. Under different crank angle, the average temperature of the cylinder increases with the increase of the inlet temperature, and the area of the high temperature region increases with the increase of the inlet temperature.(2) With the advance of fuel injection time, the combustion time of methanol, the combustion pressure, the combustion temperature increase, and the peak heat release rate increase significantly. The main reason is that when the fuel injection timing is advanced,the time of methanol mixed with the air flow in the cylinder, and the atomization evaporation will take longer time resulting to form more combustible mixture. The increase of peak value of the heat release rate will lead to the problem of the combustion noise and mechanical load.(3) With the decrease of the diameter of nozzle hole, the methanol droplet Sauter mean diameter and the spray penetration distance decreases, so the quality of the spray is better.Leading directly to the ignition delay period is shortened, the maximum combustion pressure rises, and the maximum combustion pressure occurs advanced. Besides that, the highest temperature in the cylinder increase, and the highest temperature appears advanced.But the diameter of the spray hole is too bigger, which leads to the delay burning and combustion deterioration.The results of calculation and analysis provide the basis for the design of the fuel system and the combustion control of the fuel pressure methanol engine.