Design And Spray Characteristics Of Heavy-Fuel Air-Assisted Injection System

Two-stroke engine is widely used in the field of UAV.Driven by single fuel,two-stroke engine burning heavy fuel has become an important direction of future development.However,heavy fuel high viscosity,difficult atomization and short circuit of oil and gas in two-stroke engine have become the key technical difficulties in the research.The low-pressure direct injection technology represented by air-assisted injection basically overcomes the short circuit of oil and gas,and introduces compressed air to assist the refining fuel.The high-quality atomization effect of fuel can be achieved at a low injection pressure.At present,foreign air-assisted injection system has been perfect industry,domestic is still in its infancy,the relevant research is very few.Therefore,it is particularly important to carry out the experimental study on spray characteristics of air-assisted heavy-fuel injection system under different environmental variables and injection control parameters.Based on the characteristics of two stroke aviation heavy fuel engine,this paper carried out the structural design of air-assisted injector.Based on the requirements of real-time communication and accurate fuel injection of the engine,the hardware design and software development of the fuel injection control system are carried out by using modular design.MATLAB was used to extract the complete spray contour from the collected spray image and calculate the characteristic index value of spray,which provided a quantitative research basis for the analysis of subsequent experimental results.The results show that the higher the ambient pressure is,the smaller the spray penetration distance is,and the smaller the spray cone angle in the early stage of spray development is.The higher the air injection pressure is,the larger the spray penetration distance and the larger the spray cone angle are;the larger the fuel injection duration is,the larger the fuel injection quantity is,and the smaller the spray penetration distance is;the spray penetration distance decreased with the increase of fuel-air injection interval,but it had no effect on the spray cone angle at the early stage of spray development.Too small air injection duration can not completely spray the fuel in the premixed cavity,but large air injection duration has little effect on spray penetration and cone angle.In summary,increasing ambient pressure,reducing air injection pressure and increasing fuel injection duration will reduce the penetration of fuel spray.Among them,the influence of air injection pressure on spray penetration is the most obvious,followed by ambient pressure,and the influence of fuel injection duration on spray penetration is small.