Investigation of Air Injection and Cavity Size Within a Circumferential Combustor to Increase G-Load and Residence Time

Abstract

A gas turbine combustion process subjected to high levels of centrifugal acceleration has demonstrated the potential for increased flame speeds and shorter residence times. Ultracompact combustors (UCC) invoke the high-g phenomenon by introducing air and fuel into a circumferential cavity which is recessed radially outboard with respect to the primary axial core flow. Upstream air is directed tangentially into the combustion cavity to induce bulk circumferential swirl. Swirl velocities in the cavity produce a centrifugal load on the flow that is typically expressed in terms of gravitational acceleration or g-loading. The Air Force Institute of Technology (AFIT) has developed an experimental facility in which g-loads up to 2000 times the earth’s gravitational field (“2000 g’s”) have been demonstrated. In this study, the flow within the combustion cavity is examined to determine factors and conditions which invoke responses in cavity g-loads. The AFIT experiment was modified to enable optical access into the primary combustion cavity. The techniques of particle image velocimetry (PIV) and particle streak emission velocimetry (PSEV) provided high-fidelity measurements of the velocity fields within the cavity. The experimental data were compared to a set of computational fluid dynamics (CFD) solutions. Improved cavity air and fuel injection schemes were evaluated over a range of air flows and equivalence ratios. Increased combustion stability was attained by providing a uniform distribution of cavity air drivers. Lean cavity equivalence ratios at a high total airflow resulted in higher g-loads and more complete combustion, thereby showing promise for utilization of the UCC as a main combustor.

Gear-Shaped High-g Combustion Chamber for Micro Turbojet Engine Applications

“…The minimum inner diameter was designed to be adaptable to the turbine stator of the original engine. By analyzing and summarizing previous studies, ,,, early HGCs were found to mainly consist of a main inlet, auxiliary inlet holes, and mixing guide vanes, making them relatively complex structures that cannot be easily integrated into micro turbojet engines. The new HGC structure is specific to the miniature turbojet engine, which creates a main combustion region based on the original annular flame cylinder combustion chamber so that the fuel is burned in a high- g environment.…”

“…The results showed that the combustion efficiency was not significantly affected by different jet-air angles, the combustion efficiency was still approximately 99%, and the NOx emission decreased with an increase in gloading. Cottle et al 25 added a set of injection plates and baffles to an HGC with a diffuser to control the directions and ratios of the core and secondary streams. Subsequently, Bohan et al 26,27 designed a cooling scheme by designing holes to form a cooling film and hence mitigate the localized overheating problem of the HGC.…”