Experimental Study of the supersonic exhaust diffuser spray cooling system

A supersonic exhaust diffuser provides the required test cell vacuum conditions by self-pumping of nozzle exhaust gases to the atmosphere in high altitude simulator. However, the plume temperature is often much higher than the allowable temperature of the diffuser structure. Moreover, in solid-fuel engines, the impact of aluminum oxide particles on the diffuser wall internal surfaces with high temperatures intensifies critical thermal conditions. In the present study, a spray cooling system design method is presented for a supersonic exhaust diffuser. The method is evaluated by performing several experimental tests. First, in order to identify the critical temperature region, the test of the motor with a chamber pressure of 60 bar and a chamber temperature of 3100 ° C is performed with a non-cooled metal diffuser. The results indicate that the temperature of the diffuser body in the inlet and ramp regions reaches a temperature above 1500 ° C, which leads to the melting and perforation of the diffuser in these regions. Two other tests are performed with average motor chamber pressures of 33 bar and 55 bar along with the spray cooling of diffuser body. The results show that the designed cooling system keeps the maximum temperatures of the external surface of the diffuser at the values smaller than 200 and 400 ° C in these tests. The achieved critical temperatures are well matched with the respected ones in the design procedure. This confirms the present spray cooling system design procedure.