EFFECTS OF VITIATED AIR ON HYDROGEN IGNITION IN A HIGH-SPEED LAMINAR MIXING LAYER

Abstract

One associated complication for the use of vitiated air in laboratory supersonic combustion studies to simulate flight enthalpy is that the test media are contaminated by species that are not representative of the actual atmosphere. When burning hydrogen in oxygen-enriched air is employed to produce vitiated air in experimentation, the resulting high-enthalpy airflow contains substantial amounts of, for example, H₂O, H, OH, O, and NO. Therefore, the primary objective of the present numerical study is to assess the effects of vitiated air on the ignition characteristics in supersonic experiments. Specifically, the ignition evolution in the high-speed hydrogen/air laminar mixing layer is computationally simulated using detailed chemistry and transport properties. Individual and combined influences of important contaminants on ignition are systematically examined over a range of pressure, air temperature, and freestream velocity variations. Vitiations of the active radicals, like H, O, and OH, are found to enhance ignition, as expected. Results also show that contamination of H₂O and NO can inhibit and promote supersonic ignition, respectively. The computed results on the net effect of simultaneous contaminations of H, O, OH, H₂O, and NO on the ignition response further provide insight into the interpretation of the experimental data using the vitiated air facilities.

Keywords:

• vitiation effects
• supersonic ignition
• laminar mixing layer