Experimental Study On Atomization Characteristics Of Diesel Engine Under Different Environmental Pressure And Temperature

As an important commercial and military machine,diesel engine plays an important role in today’s society.Due to the huge differences in the working environment of the diesel engine,there are no shortages of high-altitude and plateau conditions to ensure that the diesel engine can work stably and efficiently in a variety of environments.It is of great significance to civilian and military vehicles.The power and thermal efficiency of the engine largely depend on the combustion effect,and the combustion effect is determined by the atomization of the fuel and the mixture of oil and gas,so it can be said that the fuel atomization effect and the oil and gas mixing effect in the diesel cylinder determine the performance of the diesel fuel.In the cold and plateau conditions,this relationship becomes more apparent.For the atomization and break up mechanism of diesel fuel,a lot of research has been done.However,the environment temperature and pressure simulated by most of the spray experiment have not reached the actual conditions in the cylinder when the diesel engine in operation,since the analyses are mostly based on the cold spray characteristics,which cannot accurately reflect the atomization process of diesel fuel.Analysis of the atomization characteristics of diesel must focus on the analysis of the phase change process of the spray,and from the point of view of the gas phase and liquid spray characteristics,in order to have a clearer understanding of the fuel evaporation and hydrocarbon mixing process.In this paper,a visualized spray experiment platform was established,in which the high pressure constant volume bomb and the heating system enabled the spray environment to reach an ambient temperature of 800K or more and an ambient pressure of 6MPa or more,fully reproducing the in-cylinder environment at the time of diesel injection.A high-quality spray process schlieren image is obtained through an image acquisition system and a schlieren system.This article developed a set of spray image processing program,which can accurately extract the characteristics of the image parameters,and achieve the distinction between gas-liquid two-phase spray,to provide a basis for the study of fuel phase transition process and oil-gas mixture characteristics.In this paper,the free spray process under different ambient pressure conditions is analyzed.By studying the characteristics of spray gas profile changes and the characteristics of gas-phase spray,the effect of environmental pressure on the process of fuel evaporation is revealed;The influence of environmental pressure on the spray disruption process was analyzed,and the spatial development characteristics and phase transition process of wall impact spray were analyzed.The results show that with the increase of the ambient pressure,more liquid sprays undergo phase transition and form mixed gas with the surrounding medium gas,which is beneficial to oil and gas mixing and combustion.When the ambient pressure is low,the fuel spray hits the wall surface,and the lower the ambient pressure is,the greater the accumulation of liquid fuel formed on the wall surface is not conducive to secondary evaporation of the wall-attached fuel.At the same time,the fragmentation process of spray and droplet impacted on different temperature wall surfaces was studied.The results show that:with the increase of wall temperature,the size of satellite droplets formed by droplets hitting the wall is smaller,droplet life is shorter,and evaporation occurs,faster.At the same time,this paper studies the role of ambient temperature in fuel atomization,and analyzes the changes of fuel evaporation and liquid phase spray at different ambient temperatures.The results show that the ambient temperature is very important for fuel atomization and oil-gas mixing.When the ambient temperature is lower than 450°C,the heat absorbed by the fuel during spraying is small,and the fuel spray is mainly liquid.When the ambient temperature is increased to 475°C,the evaporation of fuel has changed dramatically,and the proportion of liquid spray has decreased.