Experimental investigation on the effects of fuel–air mixture temperature on the air-assisted kerosene spray characteristics

The air-assisted fuel injection (AAFI) system may be installed in the spark ignition aviation piston engine for the atomization of heavy fuels. However, studies on the effects of fuel–air mixture temperature on the spray characteristics are insufficient, which affects the design of AAFI engines. This study experimentally investigates the air-assisted kerosene spray characteristics over a wide range of fuel–air mixture temperatures (253–353 K). A high-speed backlit imaging technique was employed to monitor the temporal and spatial evolution of the spray, and a phase Doppler particle analyzer was used to measure the diameter and velocity of droplets. The results indicate that at low temperatures, room temperature, and high temperatures, the spray adopts a slender cylindrical, fusiform, and conical shape, respectively. As the fuel–air mixture temperature increases from 253 K to 353 K, the spray penetration and width first increase and then decrease. Moreover, the diameter and velocity of the droplets follow log-normal distributions. In particular, as the fuel–air mixture temperature increases, the probability that a droplet's diameter is within the range of 0–10 μm increases from 34.7 % (253 K) to 59.8 % (353 K), while the probability that a droplet's velocity is within the range of 0–10 m/s decreases from 44.1% (253 K) to 38.1% (273 K), and then increases to 57.5 % (353 K). Accordingly, as the fuel–air mixture temperature rises, the Sauter mean diameter of the droplets decreases, while the mass-average velocity of the droplets first increases and then decreases. The proportion of droplets with Stokes numbers less than 1 is positively correlated with the fuel–air mixture temperature, thus implying that droplets at high temperatures tend to follow the airflow, whereas droplets at low temperatures tend to move along their initial trajectories.