How is thrust increased in a jet engine?
The engine never runs with a perfect fuel/air ratio. The engine normally runs slightly lean when it is running at a steady speed. To speed it up, you increase fuel flow, and the engine produces more power and speeds up until the fuel/air ratio is again slightly lean. All you have to do is design the engine so that it is stable with a slightly lean fuel mixture, rather than with a perfect fuel mixture. That way you can enrich the ratio to a perfect mixture to speed the engine up. In the normal state, there won’t be quite enough fuel to consume all the incoming air, but that’s okay.
