Heat and mass transfer mechanistic investigation of wall intervention on spray ignition characteristics under aviation piston engine-like conditions

The interaction between spray and walls significantly influences the mixture formation and ignition characteristics in aviation piston engines, primarily due to the dynamics of heat and mass transfer. To elucidate the wall's influence on the impingement spray ignition process and reconcile discrepancies in the extant literature, we conducted a comprehensive suite of optical experiments encompassing free and impinging sprays with wide ambient temperature conditions (680 to 1200 K). Numerical simulations were utilized to dissect the flow field's distribution patterns, as well as heat and mass transfer dynamics. Our investigation reveals that impinging sprays exhibit markedly shorter ignition delay times than free sprays under comparable conditions, with this divergence becoming more pronounced at lower ambient temperatures. Notably, impingement sprays are capable of auto-ignition at reduced ambient temperatures. The spray-wall interaction effect accelerates the accumulation of heat from the low-temperature reaction, facilitating swifter attainment of the threshold temperature for the high-temperature reaction. This is attributable to the generation of a higher quantity of high-temperature mixtures with a diminished local equivalence ratio. The disparity in the ignition delay times between impinging and free sprays is exacerbated by the elevated heat demand for the transition from low-temperature reaction to high-temperature reaction at lower ambient temperature conditions, predominantly driven by the exothermic nature of low-temperature reaction.