Influencing Factors on Propulsive Performances of Water Droplets for Laser Propulsion

Abstract

A transversely excited at atmospheric pressure CO 2 laser operated at 10:6 m and 5 s pulse width was employed to ablate atomized water droplets for laser propulsion. The momentum was derived from the force sensor data. Experimental results indicated that coupling coefficient C m , specific impulse I sp , and internal efficiency were increased remarkably. The maximum value of C m was 52:1 dyne=W. The measured value of I sp was 102 s. Internal efficiency of 26.1% was achieved. Total impulse I and coupling coefficient C m were dependent largely on the droplets' Sauter mean diameter and speed and their combined interaction. Specific impulse I sp and internal efficiency were dependent on the droplets' Sauter mean diameter, speed, flow rate of liquid propellant feeding system, and their combined interaction. The flow rate of the liquid feeding system dominated the influencing factors on specific impulse I sp and internal efficiency .Nomenclature C m = momentum coupling coefficient D 32 = Sauter mean diameter E = the pulse-to-pulse energy F = force imparted to the nozzle g = the acceleration of gravity I = impulse imparted to the nozzle I sp = specific impulse v = mean speed of water droplets = absorption coefficient m = supplied droplet mass each time = internal efficiency = water mass density th = explosion threshold of water m = transmissivity of incident laser