Jeffrey Goldmeer Venkat Tangirala Anthony Dean GE Global Research Center, 1 Research Circle, Niskayuna, NY 12309 System-Level Performance Estimation of a Pulse Detonation Based Hybrid Engine A key application for a Pulse detonation engine concept is envisioned as a hybrid engine, which replaces the combustor in a conventional gas turbine with a pulse detonation combustor (PDC). A limit-cycle model, based on quasi-unsteady computational fluid dynamics simulations, was developed to estimate the performance of a pressure-rise PDC in a hybrid engine to power a subsonic engine core. The parametric space considered for simulations of the PDC operation includes the mechanical compression or the flight conditions that determine the inlet pressure and the inlet temperature conditions, fill fraction, and purge fraction. The PDC cycle process time scales, including the overall operating frequency, were determined via limit-cycle simulations. The methodology for the estimation of the performance of the PDC considers the unsteady effects of PDC operation. These metrics include a ratio of time-averaged exit total pressure to inlet total pressure and a ratio of mass-averaged exit total enthalpy to inlet total enthalpy. This information can be presented as a performance map for the PDC, which was then inte- grated into a system-level cycle analysis model, using GATECYCLE, to estimate the propul- sive performance of the hybrid engine. Three different analyses were performed. The first was a validation of the model against published data for a specific impulse. The second examined the performance of a PDC versus a traditional Brayton cycle for a fixed combustor exit temperature; the results show an increased efficiency of the PDC relative to the Brayton cycle. The third analysis performed was a detailed parametric study of varying engine conditions to examine the performance of the hybrid engine. The analysis has shown that increasing the purge fraction, which can reduce the overall PDC exit temperature, can simultaneously provide small increases in the overall system efficiency. DOI: 10.1115/1.2771246 Keywords: pulse detonation engine, pulse detonation combustor, hybrid engine, perfor- mance estimate Introduction The aviation industry recently celebrated its 100th anniversary of flight. The piston engine powered the first 50 years of aircraft propulsion. The second 50 years of propulsion have been domi- nated by the gas turbine, which has evolved into a very efficient, durable, versatile, and environmentally friendly power system. A renewed study of detonations and supersonic combustion phe- nomena in the past decade, however, may be defining the next generation of propulsion technology advancement. Not only is the combustion efficiency greater for a detonation versus the typical constant pressure process; it also contributes to pressure rise, con- sequent to the completion of detonative combuston in a confined chamber. The most far-reaching application would be to merge the strengths of current gas turbines with constant volume combustion in a hybrid propulsion system. In the ultimate embodiment of this concept, the entire/partial high-pressure core of a commercial en- gine may be replaced by a pressure-rise combustion system, as shown in Fig. 1. The interaction of a pulsed detonation combus- tion PDC system and turbine is a matter of considerable com- plexity. While there is considerable experience in ensuring that the turbomachinery operates very efficiently under steady sate condi- tions, there is little experience base with regard to the operation of a turbine with unsteady inlet flow conditions in addition to strong wave impingement on the stator and rotor blades of the turbine. The output of the pulse detonation engine PDE system is a cycle consisting of fill, detonation, blowdown, purge, and refill. The turbine experiences a wide range of inlet conditions consisting of a very strong pressure pulse, a period of relatively high tempera- ture, and a phase of low temperature and pressure corresponding to purge and refill. Turbomachinery has experienced a very sig- nificant evolution in terms of performance for steady-state condi- tions. Given a specific inlet condition, highly efficient turbine staging can be applied to produce good performance. For the PDE, there will be brief periods when the turbine can operate at these very high efficiencies, but this will need to be counterbal- anced with the need to provide acceptable performance during nonoptimal phases of the cycle. A classical thermodynamic analysis thermodynamic-state ap- proach or, more precisely, entropy method 1,2 calculates the performance of an unsteady engine operating in a cycle from en- tropy increments for each process based on thermodynamic cycle alone. This method is based on the fact that for steady flows, the difference in kinetic energy between the inlet and exit planes is equal to the work done by the medium. Automotive engine cycles have successfully used this thermodynamic-state approach pressure-volume or temperature-entropy charts because the en- ergy balance is greatly simplified by neglecting the kinetic energy of the working fluid, and wave dynamic/fluid mechanics consid- erations are not necessary to calculate the performance metrics such as thermal efficiency and fuel-specific impulse I SP,f . Although the calculation of performance using the entropy method is thermodynamically sound, this analysis is similar to a Contributed by the International Gas Turbine Institute of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 21, 2006; final manuscript received May 1, 2007; published online December 26, 2007. Review conducted by Dilip R. Ballal. Paper presented at the ASME Turbo Expo 2006: Land, Sea and Air GT2006, Barcelona, Spain, May 8–11, 2006, Paper No. GT2006-90786. Copyright © 2008 by ASME