Research on Performance of Pulsed Twin-Fluid Injector and Its Application on a Spark Ignition UAV Engine

The principal objective of the present work is to investigate the fundamental characteristics of a commercially available outwardly opening twin-fluid injector, which utilizes air-assisted atomization principle to attain pulse-type injection of fuel-air mixture. The electromagnetic characteristics of this injector were simulated and the effects of dominating parameters on the electromagnetic force to drive injector were ascertained. On that basis, this paper elaborates on the fundamental characteristics of air-assisted spray using gasoline and kerosene with the employment of two types of optical testing techniques. The spray morphological evolution under varied fuel injection durations and ambient pressures were captured with high-speed shadowgraph thus the corresponding external macroscopic characteristics were obtained and further compared. Spray droplet velocity and diameter at fixed monitoring location were measured by using PDPA (Phase Doppler Particle Analyzer). The results indicate that the gas-phase flow in the spray field possesses a comparatively high velocity, which makes the spray highly turbulent with the calculated Reynolds number ranging in the order of 10⁴-10⁵. The arithmetic mean diameter of spray droplets was found to increase as the injection duration increases, and also increase as the ambient pressure increases. Due to the negative impact of relatively high fluid viscosity on liquid disintegration, the diameters of kerosene spray droplets are generally larger than that of gasoline under the same working conditions. The twin-fluid injector was applied to an unmanned aerial vehicle engine prototype and the combustion and engine performances of gasoline and kerosene were compared. Under the premise of ensuring stable operation of the engine, it was found that the combustion of kerosene lagged behind gasoline apparently, and the power performance was also inferior to gasoline.