Performance of a Pulse Detonation Combustor-Based Hybrid Engine

Abstract

A key concept envisioned for Pulse Detonation Engine (PDE) technology is a hybrid engine, where a Pulse Detonation Combustor (PDC) replaces the combustor in a conventional gas turbine. A systems level performance estimation model for a PDC-based hybrid engine cycle was presented. A variable property formulation was used to estimate the cycle performance parameters namely the thermal efficiency (ηth) and the net specific work (Wnet). Performance estimations were obtained using a one-step finite-rate chemistry to simulate reactions, and the frozen reactions assumption to model the products of combustion. Two specific parametric studies are performed in which the compression ratio (CR) and the purge fraction (pf) were systematically varied. The predicted variations of ηth and Wnet with varying compression ratio and purge fraction are in agreement with the trends reported in the literature. For a range of values of CR (1-40), performance (ηth) advantage of a PDC-based hybrid engine is predicted, when compared to a conventional gas turbine engine. The present calculations show that the assumed unsteady turbine component efficiency (ηT) for the case of a PDC-based hybrid engine has a large effect on ηth. An experimental study investigating the operation of a multi-tube PDC-turbine hybrid system was performed to understand the effect of unsteady flows entering the turbine on the turbine component performance (ηT). An eight-tube PDC can-annular configuration was integrated with a single-stage axial turbine nominally rated for 10 lbm/s, 25000 RPM and 1000 hp. The system accumulated a total of 144 minutes of operation with long duration runs of approximately 5 minutes, in order for the rig to achieve thermal steady state and for the turbine to attain constant speed. The turbine component efficiency was found to be similar under PDC-fired operation and steady flow operation within the uncertainty of the measurement.