Mechanistic Investigation of Wall Intervention on Spray Ignition Characteristics Under Aviation Piston Engine-Like Conditions

Abstract

Spray-wall interaction (SWI) directly affects SWI directly affects the in-cylinder mixture formation and ignition characteristics of aviation piston engines. To achieve a thorough comprehensive underlying of how the wall effect affects the spray ignition process and to provide clarity on the contradictory findings reported in prior investigations, an extensive series of optical diagnostic tests encompassing both free sprays and impingement sprays was systematically conducted across a wide temperature range (680 ~ 1200 K). Numerical simulations were employed to analyze the distribution patterns of the flow field, temperature, and equivalent ratio. The results reveal that SWI leads to a larger vapour-phase spray volume, which promotes air entrainment and facilitates mixture formation. Under identical conditions, the impingement spray demonstrates significantly reduced ignition delay times (IDTs) compared to the free spray. Furthermore, this disparity in IDTs is found to be more pronounced under lower ambient temperatures. Furthermore, the impingement spray demonstrates lower ignition-limiting ambient temperatures. SWI accelerates the buildup of heat from the low-temperature reaction (LTR) process and reaches the threshold temperature for the high-temperature reaction (HTR) sooner because it produces more high-temperature mixtures with a lower local equivalent ratio. The disparity in IDTs between the impingement spray and the free spray is amplified by the increased heat needed for the LTR-to-HTR transition at lower ambient temperatures, primarily due to LTR exothermic reactions.

Keywords: SWI, impinge, spray, ignition, IDT