Suppression of the back-propagated pressure waves originated from a liquid-fueled valveless pulse detonation combustor with combined aero-valves

In order to seek out a way to isolate the back-propagated pressure waves originated from a valveless pulse detonation combustor (PDC), a liquid-fueled single tube PDC was designed and tested at frequencies ranging from 10 Hz to 30 Hz with different types of aero-valve installed at the air inlet such as wedge-shaped aero-valves, reflux-typed aero-valves and combined valves. The damping ability of the aero-valves were quantified and compared. Then, an isolator was designed and combined with the optimized aero-valves to isolate the back-propagated pressure waves. The experimental results show that both the wedge-shaped aero-valve and the reflux-typed aero-valve could reduce the peak value of the back-propagated pressure waves and the pressure oscillation at the air inlet. The largest pressure oscillation was reduced from (74.7 ± 3.35)% to (25 ± 1.84)% when three wedge-shaped aero-valves was installed at the inlet section, while the pressure oscillation was only (22.3 ± 2.9)% with three reflux-typed aero-valves. What's more, the pressure oscillation at the air inlet could be further reduced with the combination of the wedge-shaped aero-valve and the reflux-typed aero-valve. The combined structure 6 (one wedge-shaped aero-valve + two reflux-typed aero-valves) was the most effective way to reduce the pressure oscillations at the air inlet even though the peak value of the back-propagated pressure waves at the air inlet for the combined structure 6 were the highest. When an isolator was installed on the base of the combined structure 6 and the structure F (three reflux-typed aero-valves), the back-propagated pressure waves could be isolated under the case of high inlet total pressure such as a firing frequency of 30 Hz. But there are still pressure oscillations for the firing frequencies lower than 25 Hz because of that there is no supersonic region in the air inlet or the Mach number of supersonic regions is very small at low firing frequencies.