Self-Ignition Behaviors of Preheated Kerosene Following Flameout in a Scramjet

Scramjets are susceptible to unplanned flameout under large-scale attitude maneuvers, and the fuel self-ignition after flameout without igniter assistance following inflow recovery is a primary concern for evaluating engine operational stability. Direct-connect ground tests were conducted to investigate self-ignition characteristics of preheated kerosene (25–250°C) after flameout in Mach 2.0 supersonic airflow. The inflow total temperature (1255–1452 K) and Mach number were calibrated in situ via absorption spectroscopy. Measurements from wall pressure, high-speed photography, and planar laser–induced fluorescence yielded self-ignition limits and delay times. A minimum delay of 374 ms was attained at an equivalence ratio of 0.80 (1452 K). Increasing the inflow total temperature from 1255 to 1371 K reduced the minimum requisite fuel temperature for successful self-ignition after flameout (reignition) from [Formula: see text], decreasing the delay from 1.05 to 0.61 s. Furthermore, an ignition limit model based on cavity shear-layer residence and ignition delay times was developed. It revealed that inflow total temperature sensitivity was dominant, significantly exceeding fuel and wall temperatures. Even considering hot-wall effects, the critical Damköhler number for reignition remained less than unity, which was attributed to cavity residual radicals accelerating reactions. This study substantiates scramjet optimal design under high-maneuver conditions.