| Ethanol and ethyl fuels is clean alternative fuel, it is in line with Chinese condition, it can effectively solve the environmental pollution and oil shortage. From various angles, a lot of research work is done in the engine laboratory, Vehicle Department of Taiyuan University of Technology. DME-diesel blended fuel increases the viscosity of pure DME, takes advantage of low emission and high thermal efficiency. DME is obtained by the dehydration of methanol. DME containing a certain amount of methanol is called impure DME. This thesis studied on the combustion and emission performance of the blended fuel of impure DME and diesel.Firstly, to meet the anti-wear requirement of the fuel supply system, this thesis analyzed the viscosity of the blended fuel, determined the proportion of diesel with70% in the blended fuel; analyzed the mutual solubility of the blended fuel, determined the maximum possible mutual solubility of methanol in different proportions of diesel and dimethyl ether; calculated the low calorific value of the blended fuel, determined the change in oil supply pump; analyzed the saturation vapor pressure and the cost of the blended fuel, the results showed that low cost and the saturation vapor pressure of the blended fuel is beneficial in the diesel engine. For the special physical and chemical properties of the blended fuel, the fuel supply system on the original engine was modified and designed to ensure that the blended fuel can apply to the original machine.The effect of methanol content in the DME-diesel blended fuel on the combustion and emissions performance was studied through the experiment. When the methanol content was little, the power of engine increased 0.6% to 1.1%; when the methanol content was more than a certain amount (2%), the dynamic decreased with the increase of methanol content, the blended fuel containing 10% methanol fuel decreased by 0.5% to 2.4% than D30. The peak of heat release rate curve decreased, the heat release rate curve of the blended fuel delayed, ignition delay period extended and shorten the combustion duration, and they were obvious especially in low load conditions. NOx emissions was slightly decreased, the CO,HC and smoke emissions seriously deteriorated in the low load conditions, so CO,HC and smoke emissions are needed to take measures to control in the low load conditions.Through increasing the temperature of intake air, atomization performance of methanol was improved, CO,HC and smoke emissions were decreased. By reducing the ventilation area of intercooler, the cooling effect of the intercooler was reduced to raise the intake air temperature. As the temperature of intake air increase, the max cylinder pressure increased, the crank angle of cylinder pressure peak was earlier, the cylinder pressure of premixed combustion decreased, and they were obvious in the low speed load conditions. The temperature of intake air was raised, dynamic performance was slightly improved, CO,HC and smoke emissions decreased, the largest decline of CO emissions was 28.6% at low load conditions 2200r/min, NOx emissions have little change, the maximum variation was within 5%. EGR on the combustion and emissions of the blended fuel was studied in this thesis. As the EGR rate increased, the cylinder pressure of premixed combustion, the maximum of combustion pressure and temperature were decreased, the crank angle of the peak delayed, ignition delay and combustion duration extended. NOx emissions decreased significantly, when the EGR rate exceeds a certain value, CO and HC emissions will increase rapidly.The simulation analysis for blended fuel is done by using AVL-FIRE software. It verified that by increasing the temperature of intake air and reducing the fuel injection nozzle diameter, the blended fuel and air can mixed better, this method can effectively reduce the amount of CO. This simulation provides some support for follow-up application and research of impure DME.
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