P&W-led team developing powerplant for possible use in supersonic strike missiles

Tests of an advanced pulse detonation engine (PDE) design are coming closer than ever to proving the viability of the concept. Potential applications range from supersonic unmanned combat air vehicles, supersonic strike missiles, hybrid turbofans and a duct-burning single stage to orbit powerplant.

Tests of the PDE design are mid-way through their final phase at the US Naval Air Weapons Center, China Lake, California, under a three-year navy risk-reduction programme. The Pratt & Whitney-led team includes Boeing Phantom Works and United Technologies Research Center, and is focusing on tests of a five-tube PDE design which is conceptually close in size to an engine for a possible navy supersonic strike missile.

Potential benefits of the PDE include low-cost operation and acquisition, almost instant acceleration/deceleration and very few moving parts. PDEs operate by injecting a propellant mixture into a chamber that is open at one end. The mixture is ignited by a spark plug, in this case from a Formula 1 racing car, and the burning fuel rapidly generates a detonation wave that travels through the chamber before the gas from the combustion has time to expand. The explosive pressure from the detonation pushes the exhaust out of the open end of chamber, providing thrust.

The five-tube PDE is connected directly to a pressurised air supply simulating Mach 2.5 inlet pressure and temperature conditions. "We separate the inlet from the unsteady combustion process using a patented valve," says Gary Lidstone, propulsion programmes manager at P&W Seattle Aerosciences Center, Washington. The rotary valve, resembling a bowtie, is spun at 18,000RPM to match the 60Hz operating frequency of each tube, and is fed with ethylene, oxygen and compressed air. The valve modulates the firing sequence with each tube firing every 16.6ms, meaning the engine as a whole fires every 3.5ms.

Although aimed at initial operation and performance demonstration, the small test PDE is already generating between 500lb (2.23kN) and 600lb thrust in each 0.6s firing.

Source: Flight International