Experimental research of air-throttling ignition for a scramjet at Ma 6.5

An experimental investigation on ignition characteristics with air-throttling in an ethylene-fueled scramjet under flight Ma 6.5 conditions was conducted. The dynamic process of air-throttling ignition was explored systematically. The influences of throttling parameters, i.e., throttling mass rate and duration, were investigated. When the throttling mass rate was 45% of the inflow mass rate, ambient ethylene could be ignited reliably. The delay time from ignition to throttling was about 45-55 ms. There was a threshold of throttling duration under a certain throttling mass rate. It was shorter than 100 ms when the throttling mass rate was 45%. While a 45% throttling mass rate would make the shock train propagate upstream to the isolator entry in about 10-15 ms, four lower throttling mass rates were tested, including 30%, 25%, 20%, and 10%. All of these throttling mass rates could ignite ethylene. However, combustion performances varied with them. A higher throttling mass rate made more ethylene combust and produced higher wall pressure. Through these experiments, some aspects of the relationships between ignition, flame stabilization, combustion efficiency, and air-throttling parameters were brought to light. These results could also be a benchmark for CFD validation.