Operating characteristics and propagation of back-pressure waves in a multi-tube two-phase valveless air-breathing pulse detonation combustor

In order to investigate the feasibility of a pulse detonation turbine engine with a pulse detonation combustor (PDC) as a duct heater, a four-tube two-phase gasoline/air valveless PDC was designed and tested to investigate the operating characteristics and back-propagated pressure waves of the four-tube PDC. Through careful design of the four-tube PDC, successful and stable operations of the four-tube PDC under different firing patterns are realized. Two different firing patterns were tested at frequencies ranging from 5 Hz to 25 Hz: all tubes firing simultaneously, and all tubes firing sequentially. A detailed discussion of propagation of back-pressure waves in the air plenum chamber is presented and tube-to-tube interactions are quantitatively evaluated. The results reveal that the average peak pressures in the air plenum chamber with the sequential firing pattern are much smaller than with the simultaneous firing pattern. The percentage of relative peak pressure in the air plenum tends to reduce in general as the frequency is increased, which is very different to the variation of the average peak pressure. The maximum percentage of relative peak pressure under the simultaneous firing pattern was 87.26%, while it was only 34.4% for the sequential firing pattern. Investigation of tube-to-tube interactions show that the back-propagated pressure waves propagate upstream and diffract into the adjacent tubes under the sequential firing pattern. The average peak pressure of the diffracted waves in tube 1 increases as the frequency is increased, while the percentage of the relative peak pressure in tube 1 shows a smaller but similar trend when compared with that in the air plenum chamber. The maximum value in tube 1 was 23.7% and the minimum was only 7.8%.