Afterburner Ignition Delays at Altitude
Last year I read through a document from the early 50's about the characteristics of starting an afterburner at altitude. What I
can't understand is why it generally takes longer for AB light-off the higher up the aircraft is. What occurs in the AB duct that prolongs ignition?
The way I see it is that if fuel is added to the AB duct and it fails to ignite, it is simply blown out of the engine, so regardless of
how much fuel is added and for what duration, ignition should not take place no matter how much time has elapsed, however this is not the case in reality.
I initially thought that vapourised fuel would recirculate in a region down stream but in fairly close proximity to the flameholder. The recirculation would allow stable burning of the fuel to take place, however from what I recall the document mentioned delays of 8 seconds or more for AB light-off, so I doubt the vapourised fuel could be held in this state for such an extended period of time, without being blown out of the duct. So again I wonder what is happening in the duct that will cause ignition to be so laboured?