Numerical study of flame recession and stabilization in laser-ignited hydrogen jets under high-temperature and high-pressure conditions

This study adopts a gaseous Lagrangian particle tracking (LPT) method for high-pressure hydrogen direct injection. A skeletal H 2 /air/NO x chemical mechanism is incorporated to investigate flame recession and stabilization under conditions relevant to compression-ignition engines. The method is validated against laser-ignited hydrogen-jet experiments and shock-resolved simulations. Results show that the gaseous LPT method reproduces cold-jet penetration, lift-off evolution, and downstream mixing while substantially reducing computational cost. The effect of ambient oxygen concentration on flame dynamics and NO formation is then examined. Reducing the oxygen concentration from 21% to 15% (vol.) increases the lift-off length and delays upstream flame recession. Flame-front and budget analyses reveal a triple-flame structure, with the reaction source term remaining dominant along the flame front, while convection and diffusion terms mainly modulate flame position and shape. Pathway-resolved NO analysis shows distinct roles of the NNH and N 2 O routes, and higher oxygen markedly enhances overall NO formation.