Abstract:
The non-stationary self-ignition of a hydrogen-air mixture that has not been prepared in advance in a high-speed flow is considered in order to clarify the effect of the fuel excess factor on ignition and combustion stabilization in the channel. A series of experiments in a wide range of fuel excess factors of 0.35 $\div$ 1.2 showed that the initial ignition occurs in the boundary layer separation zone under the influence of a re-reflected bow shock wave in front of the fuel jet. This zone is a stable ignition source, from which the flame, under certain conditions, propagates upstream to the channel entrance. There are two combustion stabilization modes at an injection angle of 45$^{\circ}$. At low fuel excess factors, a flow with a monotonic pressure increase is realized until a plateau with a moderate pressure increase is reached. At a fuel excess factor of more than 0.8, a two-stage combustion mode is realized. The first stage consists of the heat supply process, which coincides with the combustion mode at low excess fuel coefficients and is characterized by an increase in pulsations due to increased thermoacoustic interaction. As a result of the increase in pressure in the initial ignition region, the flame front rapidly propagates up and down the flow and the pressure increases to maximum values at high combustion completeness. A comparative analysis of the pressure and heat flux distribution along the channel length is performed.
