Supersonic Jet Ignition

Abstract

Motivated by the fact that turbulent jets from straight nozzles could ignite a lean (0.5 < ϕ < 0.9) main chamber reliably as discussed in Chap. 2, we wanted to explore the possibility to reach ultra-lean limit using supersonic jets. The same experimental setup that uses a dual-chamber design (a small pre-chamber resided within the big main chamber) was used except the straight nozzles were replaced by converging or converging-diverging (C-D) nozzles. The primary focus was to reveal the characteristics of supersonic jet ignition, in comparison to subsonic jet ignition. Another intention behind supersonic jets was from ignition delay standpoint; a high-speed jet could well reduce the ignition delay. Simultaneous high-speed schlieren photography and OH* chemiluminescence were applied to visualize the supersonic jet penetration and ignition processes in the main chamber. Infrared imaging was used to characterize the thermal field of the hot jet. Numerical simulations were carried out using the commercial CFD code, Fluent 15.0, to characterize the transient supersonic jet, including spatial and temporal distribution of species, temperature and turbulence parameters, velocity, Mach number, turbulent intensity, and so on. The present work focuses on the effect of supersonic jets on lean flammability limits.