Study Of Spray Impingement Characteristics And Combustion Characteristics For Diesel Engine At High Altitude

China has a wide distribution of the plateau, an altitude of 3,000 meters above the plateau area accounts for about 26% of the total area. With the increase of altitude, atmospheric pressure drops, air density and oxygen content decrease. When diesel engine is used at high altitude, spray penetration increases, resulting in intensifing of spray impingement, increasing of wall film mass, raising of fuel-air mixture concentration in near-wall region, adding of delayed combustion period, decreasing of power, increasing of fuel consumption rate, increasing of thermal loading.According to the above problems, it is necessary to carry out the study of spray impingement characteristics and combustion heat release mechanism for diesel engine at high altitude.Firstly, in order to verify the prediction accuracy of spray impingement model under high ambient pressure, constant volume spray impingement experiment system under high ambient pressure was established. On this basis, the influence of injection pressure, injection holes, ambient pressure, wall shapes and wall temperature on spray impingement were studied through experiments.Build a series of characteristics parameters to quantitative describe the development of spray impingement, and obtain the influence of injection conditions, environmental conditions, surface characteristics on spray impingement characteristics. Construct the simulation model of spray impinging process, the simulation results of different spray impingement models are compared with the experimental results, the prediction accuracy of Bai Gosman spray impingement model is higher than others.Secondly, three-dimensional simulation software AVL FIRE was uesed to establish a turbocharged and intercooled diesel engine combustion process simulation model. Then, analyz the inner mechanism of diesel engine combustion process at an altitude of 1000m,2000m,3000m and 4000m from flow characteristics, atomization characteristics, spray impingement characteristics, fuel-air mixture characteristics and combustion heat release characteristics. In order to further analyze the influence mechanism of spray impingment on combustion process, define near-wall region in this paper, quantitatively analyze the quality distribution of fuel and oxygen, the uniformity of fuel-air mixture and heat release rate in near-wall region. Results show that when diesel engine is used at an altitude of 4000 meters, the quality of spray impingment is more, fuel vapor touched the wall of combustion chamber firstly and larger area, premixed combustion stage less heat, the concentration of fuel-air mixture is more and the peak of heat released rate is larger in near-wall region.Finally, based on the combustion process of diesel engine at an altitude of 4000 meters as the research object, the influence of injection pressure, injection holes (nozzle diameter), injection timing and nozzle spray angle on combustion process were studied from spray impingement characteristics and combustion heat release characteristics, which provides theoretical basis for improving power of diesel engine at a high altitude. The result show than when nozzle spray angle is increased and using the injector of small orifice diameter and multiple orifice so that reduce spray impingement mass,which is beneficial to improving the thermal efficiency.