Pulse Detonation Engine
The PDE is an airbreathing intermittent combustion jet engine that relies on a travelling detonation wave for the combustion and compression elements of the propulsive cycle. This engine may be used as a low cost propulsion system in drone and rpv applications or as the low speed cycle for a high Mach number combine cycle engine system. The mechanical simplicity of this engine provides low cost and high reliability, permitting use in low cost vehicles. The simple geometry of this novel engine concept naturally provides for integration into a new Combined Cycle Engine with Ramjets. The goal is to obtain an engine which operates in the Mach 0 to 3 range and integrates well with Ramjets to form a high performance Combined Cycle Engine.
The Pulse Detonation Engine, through the controlled use of strong gasdynamic waves, can be configured to provide both engine aspiration (i.e. static thrust) and relatively high charge compression. These characteristics result in several potential benefits from PDE's including 1) high thrust density, 2) high specific impulse, 3) significant static thrust, 4) natural geometry for integration into a Combined Cycle Engine, and 5) low cost.
APRI has characterized a number of PDE geometries and operating conditions that can provide good propulsion performance for static, subsonic, and supersonic applications using cycle analysis software based on numerical simulations of one-dimensional compressible gas flows including the effects of chemical reaction. The results of these simulations for various engine geometries and operating conditions are summarized.
The type of cycle considered here involves: 1) the initiation of the detonation in a tube, 2) reflection of the detonation wave/waves from the open end as expansion waves, 3) reflection of expansion fans from open end as compression waves that coalesce and reach the inlet to increase the pressure above ambient, and 4) flapper valve geometry that opens when pressure drops below ambient and closes when compression waves increase pressure above ambient.
For free flight Mach numbers 0.8 and 1.0, we simulated a "ducted-PDE" configuration that assumed the inlet and exit pressures were both equal to the stagnation pressure values. As the Mach number increased from 0 to 1 the entrainment fraction increased from 30% to over 50% and the period of oscillation increased from less than 4 milliseconds to around 5 milliseconds. The specific impulse for hydrogen-air fuel increased from 4083 seconds at M=0 to 7,341 seconds at M=1. As a rough guide to estimate performance for changes in mass consumption due to stoichiometric differences and detonation temperature differences between this hydrogen-air mixture and a kerosene type of fuel-air, we can divide the specific impulse values by 2 to get around 2000 seconds. This is somewhat better than typical turbojet/turbofan performance.
The computations indicate that the performance of PDE's should be comparable to that of turbomachinery driven propulsion systems using a simple design with few moving parts. PDE's should prove to be of low cost and highly reliable, and may be readily integrated into a combined PDE/ramjet engine configuration. APRI is currently involved in a demonstration and prototype development effort for the PDE and anticipates commercialization of this novel engine.
Inquiries concerning APRI's Pulse Detonation Engine program should be directed to Dr. Thomas Sobota at firstname.lastname@example.org