Abstract
The ignition transient phase in a model supersonic combustor with transverse fuel injection upstream of a cavity flame holder was experimentally investigated. Three types of ignition processes for scramjet startup were covered and compared: gaseous ethylene ignition, direct kerosene ignition by high-energy spark, and indirect ignition piloted by a preestablished ethylene flame. The flame propagation process and precombustion shock wave train dynamics were captured by using a high-speed camera and schlieren photography system. Three kinds of flame propagation failures were observed before a successful ignition result, after increasing the injection pressure to an ignitable pressure. The ignition limits of ethylene covered a much broader injection pressure range than ethylene when sparked directly in the cavity. The evolvement of the precombustion shock wave train for ethylene ignition indicated that the initiation of the ethylene flame was characterized by a subsonic flame expanding within the cavity. The enhanced mixing and evaporation process by the precombustion shock wave train provided another mechanism for piloted ignition, in addition to high-temperature heating of the ethylene flame.
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