Theoretical Assessment of Turbocharged Pulse Detonation Engine Performance at Various Flight Conditions

Pulse Detonation Engines (PDEs) have been found to be thermodynamically more efficient than conventional Turbojet Engines (TJEs). PDEs have performance advantages at both the subsonic and the supersonic flight speeds. PDEs differ from conventional propulsion engines in two major ways: unsteady operation and detonation combustion. To prevent detonations or shocks from moving outward through the intake and to ensure a controlled inward flow rate of fresh air into the Detonation Chamber (DC), a mechanical valve is usually provided.

            A typical PDE cycle operation includes three basic processes: initiation and propagation of detonation wave in the DC (valve closed); a quasi-steady exhaust of detonation products from the DC at varying pressure through the nozzle (valve closed); and a steady exhaust of remained detonation products at constant pressure through the nozzle while filling the DC with fresh charge (valve opened).

            Increasing the inlet air pressure increases the mass flow rate of air passing through the DC in each cycle and, as a result, it increases the total thrust developed by the engine. In the present work, a novel method of increasing the inlet air pressure by turbo-charging is proposed. A steady exhaust of detonation products from the DC during the filling process is made partly through the turbine and the remaining through the nozzle. The turbine drives the compressor which in-turn increases the inlet air pressure. To achieve the steady exhaust of detonation products partly through the turbine, ports are cut on the cylindrical surface of DC near the tail end just before the nozzle. A coaxial cylindrical drum with identical ports on it rotates over the DC so as to cover and uncover the ports of DC periodically. By running the cycle at high frequencies, the Turbocharged Pulse Detonation Engine (TCPDE) can produce enhanced quasi-steady thrust at all flight conditions. 

            The thermodynamic cycle of operation of TCPDE is analyzed based on quasi-steady state one dimensional formulation, and a computer code is developed in MATLAB to simulate the cycle performance at different compressor pressure ratios. The specific thrust and fuel-based specific impulse are estimated at various flight conditions with equivalence ratios of 0.8, 1.0, and 1.2 and are compared with those of the Turbojet engine at subsonic flight speeds and the Ramjet engine at supersonic flight speeds. Even though the total thrust produced by the TCPDE increases with an increase in compressor pressure ratio as more charge is fed into the DC in each cycle, the specific thrust and fuel-based specific impulse are found to increase up to a certain compressor pressure ratio only, and then they decrease at a given flight condition. With the increase in altitude and the decrease in flight speed, the specific thrust and fuel-based specific impulse increase up to the compressor pressure ratio of 8.0. But with an increase in flight speed (Mach number > 2), TCPDE yields the maximum specific thrust and fuel-based specific impulse up to the compressor pressure ratios of 2 to 4 only as the pressure and temperature at the inlet of compressor are already high because of the ram compression.