Experimental study of laser-ignited hydrogen jet flame evolution under simulated direct-injection diesel engine conditions

This study presents the experimental investigation of the ignition and subsequent combustion spreading sequences of hydrogen jets issued from a single-hole nozzle into a constant-volume combustion chamber. The hydrogen jet flames, forced ignited using a laser-induced plasma ignition, were monitored using high-speed schlieren imaging and pressure trace measurements. The parameters varied include the laser ignition location (axial or radial positions), laser ignition timing and the ambient oxygen level (10-21 vol.%). An analysis of the jet flame evolution reveals that the reaction front of the hydrogen jet spreads from the forced ignition site to engulf the entire downstream jet volume and recedes towards the nozzle. The results reveal that the ignition parameters and ambient oxygen condition in which it occurs can impact the jet flame recession and stabilisation characteristics. When ignition occurs sufficiently downstream or at the jet head periphery, the flame may not attain astable lift-off within the specified injection period. Additionally, lower ambient oxygen levels lead to slower flame recession towards the nozzle. Furthermore, the heat release profile of the hydrogen jet flame exhibits dependence on both the laser ignition parameters and ambient oxygen level.