The promotion of ignition in a supersonic H2–air mixing layer by laser-induced excitation of O2 molecules: Numerical study

A possibility of a considerable enhancement of ignition in a diffusion mode in a supersonic non-premixed H2–air flow by means of the laser-induced excitation of O2 molecules to the b1Σg+ electronic state is investigated on the base of numerical simulation. It is shown that for significant shortening the induction zone length it is sufficient to expose only a thin air layer (with thickness of 1–2 cm) to resonance laser radiation with a small input radiation energy 5 × 10−3–2 × 10−2 J/cm3. Even a small amount of radiation energy transmitted to the air flow makes it possible to arrange a stable combustion at a short distance (⩽1 m) from the irradiation region at a relatively low temperature of the air (T = 800 K). Shortening the induction zone length, in this case, is due to intensification of chain-branching via excitation of O2 molecules by laser radiation and penetration of excited molecules into the shear layer.