An Experimental Study On The Atomization Characteristics Of Impinging Jets Of Power Law Fluid

The special working conditions require rocket engines to carry both fuel and oxidant, and impinging jet injectors are commonly used in liquid-fuel rocket engines to obtain good mixing and combustion characteristics for fuels. In practical applications, the impingement jet could be divided into two types: symmetric and asymmetric jets. As a new type of gel propellant we choose power law fluid as working fluid, developed an impinging jet system, the spray appearances are captured by high-speed photography system, from which the breakup characteristics are extracted; Dantec’s 3D Fiber PDA system is employed to acquire 3-D velocities and size distribution of droplets; it can realize continuously measurement in a single spatial point. The effects of impingement parameters, geometry parameters and physical parameters on the atomization characteristics are studied.The experiment results show that the spray patterns in symmetric and asymmetric impingement is greatly influenced by the concentration of fluid. In our study five spray patterns occurred and they are closed rim, open rim, rimless sheet, bow shaped ligament and fully developed. In asymmetric impingement with the increment of velocity the breakup length shows doublet pattern in smaller orifice diameter, while Lbu decreases first and then increases at last decreases in a larger diameter. The spray cone angle increases with the increment of injection velocity and orifice diameter. In our experiment we keeps fluid I to be constant and the concentration of fluid II increases. At lower velocity, breakup length Lbu is inversely proportional to the fluid viscosity. In case of impingement of two jets with different viscosity Lbu is in a bimodal pattern; On the other hand, in the case of the impingement of two jets with a same viscosity Lbu is in a unimodal pattern. The spray cone angle α increases with the increment of Vj and then tends to be constant which is inversely proportion to the viscosity of fluid.In impinging jets of power law fluid the 3-D velocities of droplets increases with the increment of injection velocity. 3-D velocities of droplets in Y direction are in symmetrical distribution, and decrease in Z direction with the increment of the distance from original point, W is smaller in larger impingement angle and smaller pre-impingement length. In symmetric and asymmetric impinging jets of power law fluid Sauter mean diameter(SMD) decreases with the increment of injection velocity, SMD is in symmetrical distribution in Y direction, and in Z direction decrease in Z direction with the increment of the distance from original point. In symmetric impingement SMD in symmetrical distribution along X direction, and smaller SMD is produced by larger impingement angle, smaller pre-impingement length; in asymmetric impingement SMD increases with the increment of orifice diameter. In symmetric and asymmetric impinging jets of power law fluid the particle size distribution are both fit in the Rosin-Rammler function, with the increment of injection velocity Rosin-Rammler diameter X0 showed a trend of decrease; in symmetric impingement X0/SMD becomes about 1.3-1.5, the relative size range △S, which represents the divergence degree of droplet size increases with the increment of orifice diameter, while in asymmetric impingement X0/SMD=1.2-1.3, △S decreases with the increment of orifice diameter.