Performance Enhancement of Gas Turbine Engines Topped With Wave Rotors and Pulse Detonation Combustors

Wave Rotor (WR) acts as pressure exchanger that accomplishes both compression and expansion within a single component. In pulse detonation combustion, detonation is initiated in tubes that serve as combustors. The detonation wave rapidly traverses the Pulse Detonation Combustor (PDC) and produces a high pressure.

            In the present research work, a novel method of integrating the conventional microturbine engine with a WR and a PDC is proposed to increase the specific work and thermal efficiency of the engine. The air is compressed in a compressor. A part of the compressed air is bypassed into an ejector via a regenerator, and the remaining air is further compressed in the WR and discharged into a receiver. Fuel is injected into the compressed air. The compressed fuel-air mixture fills the PDC when the inlet valve is opened. Once the valve is closed, ignition is initiated and detonation wave propagates the PDC resulting in a nearly constant volume combustion followed by a quasi-steady exhaust of detonation products into the ejector through a nozzle to eject the gas-air mixture and a steady exhaust of remained detonation products through the WR to provide the energy transfer to compress the air. The high velocity gas jet from the nozzle ejects the exhaust gas from WR along with regenerated air through the ejector resulting in a significant gain in pressure, 20% to 25% higher than the air pressure delivered by the compressor. The ejected exhaust gas and air mixture is expanded in the turbine. The turbine is coupled to the compressor and an alternator. To achieve a steady exhaust of detonation products through the WR during the filling of PDC, ports are cut on the cylindrical surface of PDC near the tail end. A coaxial cylindrical drum with identical ports on it rotates over the PDC so as to cover and uncover the ports of PDC periodically. By running the PDC cycle at high frequencies, a steady power output with enhanced thermal efficiency can be obtained.

            The thermodynamic cycle of operation of microturbine engine topped with a WR and a PDC is analyzed, and a computer code is developed in MATLAB to simulate the engine performance with and without regeneration. The fraction of mass of air bypassed through the regenerator is adjusted such that the Turbine Inlet Temperature (TIT) is within the operational limits. For thermodynamic calculations, two un-recuperated micro-turbine engines called C-30 and C-60 made by Capstone Turbine Corporation are considered. The specific work and the thermal efficiency of the proposed engine are estimated at equivalence ratios of 0.7, 0.8, 0.9, and 1.0  and they are compared with those of the baseline engines and baseline engines topped with wave rotors only. With a WR pressure ratio of 2.0, the thermal efficiency of the baseline un-recuperated engine topped with WR increases from 15.0% to 20.5% and from 19.5% to 24.5%, respectively for C-30 and C-60 engines.  The thermal efficiency of the baseline engine topped with WR and PDC increases from 15.0% to 22.2% and from 19.5% to 26.3%, respectively for C-30 and C-60 engines.