Ignition, flame structure and near-wall burning in transverse hydrogen jets in supersonic crossflow

摘要

We have investigated the properties of transverse sonic hydrogen jets in high-temperature supersonic crossflow at jet-to-crossflow momentum flux ratios J between 0.3 and 5.0. The crossflow was held fixed at a Mach number of 2.4, 1400 K and 40 kPa. Schlieren and OH* chemiluminescence imaging were used to investigate the global flame structure, penetration and ignition points; OH planar laser-induced fluorescence imaging over several planes was used to investigate the instantaneous reaction zone. It is found that J indirectly controls many of the combustion processes. Two regimes for low (<1) and high (>3) J are identified. At low J, the flame is lifted and stabilizes in the wake close to the wall possibly by autoignition after some partial premixing occurs; most of the heat release occurs at the wall in regions where OH occurs over broad regions. At high J, the flame is anchored at the upstream recirculation region and remains attached to the wall within the boundary layer where OH remains distributed over broad regions; a strong reacting shear layer exists where the flame is organized in thin layers. Stabilization occurs in the upstream recirculation region that forms as a consequence of the strong interaction between the bow shock, the jet and the boundary layer. In general, this interaction - which indirectly depends on J because it controls the jet penetration - dominates the fluid dynamic processes and thus stabilization. As a result, the flow field may be characterized by a flame structure characteristic of multiple interacting combustion regimes, from (non-premixed) flamelets to (partially premixed) distributed reaction zones, thus requiring a description based on a multi-regime combustion formulation.