Numerical investigation of the shock-focusing detonation engines with different nozzle configurations.

This study proposes a space-marching nozzle design method based on a modified CCW relation and an auxiliary secondary injection technique for the shock-focusing detonation engine initially filled with the stoichiometric hydrogen/air mixture to improve the total impulse. First, a parametric analysis of the contraction and expansion ratios is carried out to demonstrate the positive contributions of the diverging walls to the total impulse. With the expansion ratio ε increasing from 1.5 to 2.5, the total impulses of the nozzle configurations with contraction ratios ε' = 1.11, 1.25, and 1.43 increase by 13.44%, 21.28%, and 22.82%, respectively. The combination of ε' = 1.11 and ε = 2.5 (nozzle CD9) corresponds to the maximum total impulse of 0.5754 N s and the relatively large specific impulse of 4963.9s in a single cycle of 350 μs. Second, a characteristic form of the detonation shock dynamics (DSD) is then utilized to design the diverging profile of the nozzle, further enlarging the expansion ratio and modifying the straight wall into a curved one. It can be observed that the DSD profile roughly has a 70.29% higher peak thrust, a 29.5% higher total impulse, and an 8.61% higher specific impulse than nozzle CD9. Third, an optimal distance between the primary and secondary injection slots (Δx = 10.0 mm) is introduced to improve thrust, where the total impulse and specific impulse in a single cycle reach 0.7855 N s and 5693.0s. Fourth, the inlet flow parameters are adjusted to trigger a multi-cycle operation. A combination of p t,inj = 0.45 MPa, T t,inj = 300 K, and Ma inj = 1.5 can guarantee a time-averaged total thrust of 767.3 N, a specific impulse of 5066.3s, and a dominant frequency of 3233 Hz. These results reveal the reliability of the proposed design procedure for SFDE nozzles. • The shock-focusing detonation engine has a higher operating frequency than the traditional pulse detonation engine. • The diverging section of the nozzle contributes positively to the thrust, and the converging section generates drags. • The detonation shock dynamics is used to ensure perpendicularity of the detonation foot to the diverging nozzle wall. • The secondary injection induces a recirculation zone in the diverging nozzle wall, creating a pressure plateau. • The multi-cycle operation needs a high total pressure, a low total temperature, and a large injection Mach number. [ABSTRACT FROM AUTHOR]