An experimental study on penetration and mixing characteristics of liquid fuel in preheated supersonic airflows

The effect of air temperature on the penetration and mixing of a liquid hydrocarbon fuel injected into supersonic airflows was investigated. The supersonic air of Mach 1.8 with a total temperature in the range of 373-673 K was supplied to the test section. The liquid fuel was injected into the supersonic airflow by means of an alternating -wedge pylon with a fuel-to-air momentum flux ratio of 15. A laser sheet imaging system using Mie scattering has been used to investigate the instantaneous and ensemble-averaged characteristics of the fuel plume, the fuel/air mixing process, and fuel evaporation. As the air temperature increased, the Mie scattering signal gradually weakened due to fuel-air mixing enhancement and fuel evaporation downstream of the pylon. At an air tem-perature of 673 K, most of the fuel evaporated before reaching the outlet of the test section (X/d = 703). As the air temperature increased from 373 to 673 K, the total pressure loss without fuel injection decreased from 20.6 to 15.4%. In addition, the total pressure losses due to fuel injection was about 3.5% greater than that without fuel injection. As the air temperature increased, the fuel penetration height decreased. However, at the air temper-atures higher than the fuel boiling temperature, the fuel jet/spray penetration heights were almost similar, showing little effect of temperature any further.