Originally Posted by
Check Airman
Thanks guys. Now for my second question. What exactly is an unstable flame?
Have you ever used a propane torch? When you light a propane torch (or something similar) - if you have the gas turned up a little to high, it will light but won't be stable. If it's too high the flame will blow out again, but if it's just a bit high the flame will remain but move around and not attach to the nozzle base, and will make a bit of a popping sound as it moves around. You fix it by turning down the gas a bit to allow the flame to attach to the nozzle, after which you can turn the gas back up to get a nice, strong flame to do whatever you want to do with the torch.
Getting the latest low emission combusters to light is surprisingly difficult. We spent a bunch of time working on improving the light off characteristics of the GEnx - both for 'normal' ground starts and in-flight starting.