Investigation on impact of spark single-pulse energy storage on ignition performance in a scramjet combustor

Reliable ignition of scramjet combustor has attracted extensive interest and many ignition methods with different output power have been reported. However, the exact energy level required for the igniter in a scramjet combustor and the specific effect of ignition energy on ignition characteristics has yet to be identified. In this study, ignition tests of spark ignition system with various single-pulse energy storage in a scramjet combustor fueled by liquid kerosene at low flight Mach number have been conducted. The impact of single-pulse energy storage of long electrode distance high-energy spark igniter (LHSI) on ignition limit, ignition process, and ignition probability is firstly illustrated and the energy allocation strategy of spark ignition system for scramjet is analyzed. The results show that the increase of single-pulse energy storage in spark ignition system can effectively extend the ignition limit and enhance ignition process within combustor as the energy deposited by spark plasma partially counteracts unfavorable local equivalence ratio conditions and enhances combustion reaction during ignition. The single-pulse energy storage must exceed a specific threshold (e.g., 55 J for global equivalence ratio (GER) = 0.081 and 200 J for GER = 0.256) to enable the possibility of ignition. Above this threshold, limited by the input power, spark ignition system needs to reasonably allocate energy between the single-pulse energy storage and the pulse repetition frequency to maximize ignition performance. It can be concluded that the spark ignition systems with larger single-pulse energy storage and higher discharge efficiency continue to hold significant value in scramjet combustors.