Ignition enhancement of liquid kerosene by a novel high-energy spark igniter in scramjet combustor at Mach 4 flight condition

Abstract

Spark ignition system is the most widely used method in the combustor. However, it is generally considered unsuitable for scramjet engines due to the shortage of ignition energy. This study firstly presents a novel long electrode distance high-energy spark igniter (LHSI), which significantly increases the energy deposition of spark by simultaneously improving the energy storage and discharge efficiency. The discharge and ignition characteristics of LHSI were investigated based on the discharge waveforms and high-speed photography. The results show that the discharge efficiency of LHSI can reach 62.4% with the single-pulse stored energy of 100 J while that of conventional high-energy spark igniter (HSI) is only 28.2%. The ignition process produced by such a high-energy spark is firstly reported in a scramjet combustor. An initial flame kernel with a larger size and higher combustion intensity can be produced, which is capable of igniting the cavity with proper local equivalence ratio rapidly and reliably. Compared with HSI, the ignition process of LHSI is more active and the ignition limit can be obviously extended. A novel tail flame ignition mode is observed. It can be concluded that the spark ignition with greater energy deposition is worthy to be further studied in scramjet.