Spray and droplets characteristics of air assisted nozzle under extreme low fuel temperature

To extend the range of unmanned aerial vehicles (UAVs), internal combustion engines using aviation kerosene are utilized because of its high efficiency and power density. The air assisted nozzle are used in the engines of UAVs due to the requirement of light weight. But the extreme low temperature at high altitude pose a great challenge to the air assisted nozzle because of the high viscosity and low volatility of fuel under low temperature. In this paper, a cryogenic fuel injection system coupled with an air assisted nozzle are utilized to realize the injection under low fuel temperature down to – 55 °C. The high-speed imaging and Phase Doppler Particle Analyzer (PDPA) technologies are employed to analyze the spray and droplets characteristics. Results showed that large visible droplets come out of the nozzle under low temperature, indicating the incomplete breakup inside the nozzle. The Sauter mean diameter (SMD) significantly increase from 14 μm to 25.4 μm with the fuel temperature decrease from 25°C to – 55°C, leads to deterioration in atomization and evaporation. Furthermore, increasing assisted air injection pressure and duration can reduce the large droplets and improve the atomization. Results indicate that eliminating the large visible droplets is a key issue to improve the atomization performance. The design of fuel storage grooves or threads on the inside surface of the nozzle may reduce the fuel accumulation in the exit of the nozzle and reduce the incomplete breakup.