Russia has demonstrated a pulse-detonation engine (PDE) with low-energy ignition and a specific impulse of 800s in static conditions, about half that of comparable hydrocarbon-fuelled ramjet at Mach 2.
The PDE demonstration by the Russian Academy of Sciences' Semenov Institute of Chemical Physics used a predetonator tube with a turbulence-enhancing device known as a a Schelkin spiral. The fuel was a mix of hexane and heptane.
The predetonator design enabled detonation ignition at an low energy level of 24 Joules, compared to 3,300J required for a straight tube. But in a cold start the two igniters required a total of 130J.
"This shows we can use a normal car spark plug for detonation," said academy researcher Sergey Frolov, speaking at the EUCASS 2007 European aerospace sciences conference in Brussels on 3 July.PDEs have few or no moving parts and are thermodynamically more efficient than conventional piston, turbine and ramjet powerplants, because the pressure rise inside the engine is caused by a supersonic detonation, and its subsequent shockwave, rather than combustion or deflagration at constant pressure.
Once triggered, the detonation shockwave travels through the fuel and the heat released provides the energy to sustain the wave.The engine purges itself as the wave causes the reactive gases to be expelled from the main detonation tube, allowing fresh fuel and air to be drawn in for the cycle to continue.The Russian demonstrator consisted of an igniter chamber, predetonator tube, a second igniter used only for a cold start, and the main detonation tube, which was wider than the predetonator. Its maximum operating frequency - the injection/ignition/purge cycle rate - was 8Hz. The maximum measured thrust from the main tube was 6.7lb (30N).
Problems yet to be solved to make a PDE practical include increasing the specific impulse by optimising the main detonation tube length and stabilising an operating frequency that can sustain the burning of aviation kerosene instead of volatile fuels like hexane and heptane.
Frolov's research was partly supported by the US Office of Naval Research, the International Science and Technology Center and the Russian Foundation for Basic Research.
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Source: Flight International
