Experimental Research on Two-Phase Pulse Detonation Characteristics under Elevated Initial Pressures and High-Frequency Conditions

To investigate the operating characteristics of two-phase pulse detonation engines (PDEs) under elevated initial pressures and high-frequency conditions, experiments were conducted using gasoline as the fuel and 50% oxygen-enriched air as the oxidizer. Elevated initial pressures ranging from 0.10 to 0.31 MPa have been achieved by increasing the reactant supply pressures and installing convergent nozzles with varying contraction ratios at the tube exit. The results show that, as the supply pressure increases, the stable detonation ranges both the equivalence ratio and the oxidizer-to-fuel supply pressure ratio initially widen and then narrow. All stable detonation cycles occur at supply pressure ratios below unity. Increasing the initial pressure enables stable detonation under fuel-lean conditions, with the lowest equivalence ratios decreasing to 0.495 and 0.492 for contraction ratios of 1.23 and 1.0, respectively. The nozzle with a contraction ratio of 1.56 provides the widest equivalence ratio range, spanning from 0.811 to 2.530. Moreover, increasing the initial pressure has only a limited influence on the deflagration-to-detonation transition (DDT) distance in the present study. The detonation wave pressure increases almost linearly with rising initial pressure, reaching a detonation-to-initial pressure ratio of 29.85. Furthermore, the maximum stable detonation frequency depends on both the nozzle contraction ratio and the initial pressure. A stable frequency of 100 Hz is achieved under specific initial pressure and contraction ratio conditions, while excessively large contraction ratios or significant increases in initial pressure can reduce the stable operating frequency.