Effects of pre-filled gas and spraying condition on ignition of oxygen/kerosene spray combustion

The transient characteristics of kerosene/oxygen spray were investigated using a windowed rocket combustor. In order to investigate the effects of ignition conditions, viz. aerodynamic Weber number and the oxygen fraction of pre-filled gas, on GOx/kerosene ignition, the ignition process was visualized directly using the shadowgraph technique. In addition, the dynamic pressure and global OH* chemiluminescence were measured simultaneously. The transient ignition process was significantly changed by the type of pre-filled gas (nitrogen or oxygen). The nitrogen-filled ignition condition resulted in smooth ignition, while the oxygen-filled ignition condition induced two-step ignition following the sequence of ignition with high-pressure peak, temporary extinction, and re-ignition. The ignition process was less affected by the spraying condition (Wea), except that the change of the spraying condition influenced ignition to steady state transition, such as a combustion chamber pressure overshoot. It was revealed that the oxygen-filled ignition condition caused drastic energy generation at the moment of ignition, producing a high-pressure peak and causing reverse flow of combustion gas through the gaseous oxidizer injector. This resulted in temporary extinction of the initial flame followed by re-ignition. Once the two-step ignition phenomenon occurred, the combustion chamber pressure did not increase to its steady state value during the entire run time (1.5 s). As the oxygen fraction in the pre-filled gas increased because of the increase in oxygen pre-injection time, the ignition delay time decreased and the peak value of global OH* intensity increased exponentially. When the oxygen pre-injection time became more than 14 ms, the ignition process transformed from smooth ignition to two-step ignition, and the peak value of global OH* intensity began increasing, the ignition process was converted from the smooth ignition to the two step ignition.