Fuel is injected into an airflow that is already moving.
If conditions are not just right, the flame can move out of the combustion chamber and extinguish, causing the engine to flame out. Chawla conducted several runs of the combustion experiment using a fuel mixture of 50 percent methane and 50 percent nitrogen, with differing fuel flow and air velocities. Each run produced a one centimeter blue flame, but the length of time that the flame remained stable and in the proper position varied with changes in fuel flows and air velocities. On the ground, the research team closely monitored its experiment on video sent down by the crew. First we were trying to observe how long the flame could remain stable and attached to the valve before it would pull away.