Originally Posted by
Check Airman
As usual, you've prompted another question- why are the latest combusters difficult to light off (or light up)? Or is that something I'll find out about when I look up "turbine engine combustor instability"? Thanks
Dave Therhino!
That's a tougher question. Burner and fuel nozzle design is a bit of a black art to begin with, so I suspect that the compromises that low emission requirements drive in the design are hurting the light-off characteristics. The Dual Annular Combustor design in the GE90 was driven by emissions requirements, and the GEnx uses a very elaborate staged fuel nozzle setup that mimics the low emissions of a DAC without the drawbacks of an actual DAC. But why that makes them so hard to light I don't know. What is clear however is that, compared to the late 1980's designed engines such as the CF6-80C2 and the PW4000/94", the latest generation of high bypass engines are much harder to lite - with corresponding reductions in the in-flight start envelopes. Part of it is due to the increasingly high bypass ratios - but not all.