Energy analysis and research on injection control parameter influence mechanism of air assisted spray system

•Air assisted spray model was built which fully considered the flow inside nozzle.•The gas–liquid interaction in air assisted spray was analyzed by energy analysis method.•The enhanced effect of gas expansion on the gas–liquid interaction was found.•The effect of injection parameters on spray was analyzed through energy analysis method. Air assisted spray system is a two-phase flow spray technology, which consists of fuel injector and gas injector. High pressure gas is injected into the air assisted spray system to maintain the high pressure environment. When using, fuel is injected into the system to mix with high pressure gas, and then the mixture is sprayed out through gas injector to complete the atomization process. Because the air assisted spray system can achieve better atomization of high viscosity liquid under lower injection pressure (below 10 bar), it has attracted more attention recently. A geometric model of the air assisted spray system with a complete air assisted nozzle is established. Based on this model, working process of air assisted spray system is investigated by energy analysis method, and influence mechanisms of different injection control parameters are analyzed. As discovered, the energy provided by fuel injection promotes droplet breakup after interacting with gas inside nozzle. Simultaneously, droplet transfers kinetic energy to gas. Afterwards, kinetic energy of gas and droplet is consumed during their interaction, thereby weakening gas–liquid interaction and reducing droplet breakup. After opening needle valve of gas injector, gas can obtain more kinetic energy due to the pressure difference inside and outside the nozzle, which plays a dominant role in the gas–liquid interaction, and promotes the breakup of droplets. However, the kinetic energy of gas and droplets is subsequently transferred to ambient gas, thus weakening the gas–liquid interaction and hindering the breakup of droplets. The fuel injection duration indirectly affects the consumption of gas kinetic energy in gas–liquid interaction by affecting the total amount of droplets, and then affects the characteristics of air assisted spray. The fuel-gas injection interval directly affects the consumption of gas kinetic energy in gas–liquid interaction, and then affects the characteristics of air assisted spray. The influence of gas injection duration on the characteristics of air assisted spray is determined by the influence of the flow inside the nozzle on the external