Proceedings of the Second International Energy 2030 Conference,
November 4-5, 2008, Abu Dhabi, U.A.E.

Advanced Mixing in High-Speed Flows for Efficient Combustion

A. Abdelhafez
University of Maryland, USA

A. K. Gupta
University of Maryland, USA

Abstract
The effects of convective Mach number and air-fuel density ratio have been examined experimentally under both non-swirling and swirling conditions in a free under-expanded supersonic-nozzle airflow comprising diamond shock structure with coaxial fuel injection. A convergent nozzle was used with maximum near-field Mach number of 2.0. Non-reacting conditions were considered, wherein fuel was simulated with helium and argon gases. Schlieren diagnostic technique with 6 ns exposure was implemented to allow for accurate visualization of shock structure. Two distinct diamond shock substructures were identified, namely a primary one, generated off nozzle-rim, and a secondary structure, generated off the coaxial injection system and air-fuel shear layer. The primary shock sub-structure is affected mainly by the properties of airflow, whereas the secondary structure strongly depends on the properties of injected fuel, primarily convective Mach number. The role of imparting swirl to the airflow was examined to study how flow structure and mixing are affected. Changing convective Mach number does not affect primary structure significantly; however, the secondary structure gradually diminishes with decrease in convective Mach number. No significant differences were observed with change in air-fuel density ratio.