Pressure Gain Combustion for Gas Turbines: Analysis of a Fully Coupled Engine Model

Abstract

The “Shockless Explosion Combustion” (SEC) concept for gas turbine combustors, introduced in 2014, approximates constant volume combustion (CVC) by harnessing acoustic confinement of auto-igniting gas packets. The resulting pressure waves simultaneously transmit combustion energy to a turbine plenum and facilitate the combustor's recharging against an average pressure gain. Challenges in actualizing an SEC-driven gas turbine include (i) the creation of charge stratifications for nearly homogeneous auto-ignition, (ii) protecting the turbocomponents from combustion-induced pressure fluctuations, (iii) providing evidence that efficiency gains comparable to those of CVC over deflagrative combustion can be realized, and (iv) designing an effective one-way intake valve. This work addresses challenges (i)–(iii) utilizing computational engine models incorporating a quasi-one-dimensional combustor, zero- and two-dimensional (2D) compressor and turbine plena, and quasi-stationary turbocomponents. Two SEC operational modes are identified which fire at roughly one and two times the combustors' acoustic frequencies. Results for SEC-driven gas turbines with compressor pressure ratios of 6:1 and 20:1 reveal 1.5-fold mean pressure gains across the combustors. Assuming ideally efficient compressors and turbines, efficiency gains over engines with deflagration-based combustors of 30% and 18% are realized, respectively. With absolute values of 52% and 66%, the obtained efficiencies are close to the theoretical Humphrey cycle efficiencies of 54% and 65% for the mentioned precompression ratios. Detailed thermodynamic cycle analyses for individual gas parcels suggest that there is room for further efficiency gains through optimized plenum and combustor designs.