Experimental study on the low-temperature ignition characteristics of RP-3 aviation kerosene impinging sprays

RP-3 aviation kerosene shows great potential for enhancing diesel engine cold-starts, yet its low-temperature wall-impinging ignition behavior remains incompletely understood. Thus, the ignition characteristics were examined at ambient temperatures ( T _amb) of 660–800 K in a constant volume combustion chamber (CVCC) using high-speed direct photography. Results indicate that the ignition delay time (IDT) of the RP-3 free spray decreases as T _amb increases, but slightly increases at T _amb = 780–800 K. For impinging sprays, the IDT decreases monotonically with increasing wall temperature ( T _w). The ignition position is closer to the wall vertically, but exhibits a phase-dependent non-monotonic trend horizontally. For liquid-phase impingement, higher T _w restricts film spreading, with ignition closer to the nozzle axis. For vapor-phase impingement ( T _amb > 700 K), ignition initially shifts away from the axis due to enhanced radial spreading, but retreats toward it as the wall cooling effect significantly weakens ( T _w = 473–523 K). At T _amb < 800 K, the IDT increases as the wall distance ( D _w) increases from 27 mm to 40 mm due to weakened air entrainment, but shortens at 50 mm via enhanced fuel-air premixing. Compared to the free spray, wall heat absorption delays impinging spray ignition at lower T _w (423–473 K), but the IDTs of both sprays become nearly identical at T _w = 523 K. Notably, at T _w = 523 K and D _w = 27 mm, rapid wall-film evaporation supplies additional gaseous fuel, lowering the critical ignition temperature of the impinging spray by 40 K compared to the free spray.