Mechanisms of Flame Stabilization and Blowout in a Reacting Turbulent Hydrogen Jet in Cross-Flow

Title of Thesis: INVESTIGATION OF FUEL-AIR MIXING IN A MICRO-FLAMEHOLDER FOR MICROPOWER AND SCRAMJET APPLICATIONS Kiran Hamilton Jeffrey Dellimore, Master of Science, 2005 Thesis Directed By: Assistant Professor Christopher P. Cadou Department of Aerospace Engineering This thesis presents a first principles model of the fuel-air mixing process in a micro-flameholder. This model is used to identify key design parameters involved in fuel-air mixing and to characterize how mixing performance scales with the Reynolds number. The results of this analysis show that fuel-air mixing in micro-flameholders occurs primarily at low Reynolds numbers (1<Re<5x10 3 ) traditionally associated with the laminar to transitional flow regime. Mixing lengths in micro-flameholders based solely on molecular diffusion are also predicted using a modified BurkeSchumann model. The predicted mixing lengths indicate that less distance is required for fuel-air mixing as micro-flameholders get smaller. Axisymmetric CFD simulations are performed to validate the predictions of the Burke-Schumann model, and to investigate the importance of axial diffusion and viscous effects. The results of these simulations suggest that viscous shear at the wall and at the fuel-air interface can significantly impact mixing lengths in micro-flameholders. INVESTIGATION OF FUEL-AIR MIXING IN A MICRO-FLAMEHOLDER FOR MICRO-POWER AND SCRAMJET APPLICATIONS

Investigation of fuel-air mixing in a micro-flameholder for micro-power and scramjet applications

: Single and two phase fuel injection into compressible flows was studied. Mixing was measured under a variety of injection conditions as governed by injector geometry and fuel chemistry, phase, velocity, temperature and pressure. The impact of flow conditions on the state of mixing was also investigated. Several diagnostic methods were used, including optical diagnostic techniques and mechanical probing. Combinations of mechanical probe measurements were used to calculate such flow properties as Mach number, velocity, static temperature, and species concentration. For mixing studies, both the scalar and vector quantities were measured to assess the Schmidt number effect Information obtained using laser diagnostic techniques was compared with the probe measurements. Results of the comparisons suggest that data obtained through laser diagnostic techniques and probe measurements can complement each other, contributing to the development of a broad understanding of the physical processes of running under a variety of conditions. These basic mixing studies have led to the successful development of several mixing enhancement schemes, which have been tested and reported elsewhere.

S. Dasgupta

Papers

Combustion and Mixing Studies in Compressible Flows.