Any idea how hot these fires get? 

Dan,

 

I can't tell you the exact temperature for this condition but I can bracket it for you. We generally assume hydrocarbon fueled compartment fires in buildings and ships to reach around 925 C. However this is with ventilation equivalent to an open window. The forced ventilation under the cowling would obviously increase this quite a bit.

 

I have found that copper is likely to melt in aircraft engine compartment fires, so that would push the peak temperature up to around 1000 C or more.

 

The adiabatic flame temperature of gasoline is roughly 2000 C. This value plus the ambient temperature is the theoretical upper limit under any condition. It is also virtually unattainable since it requires a perfectly insulated leak tight enclosure with nothing but a stoichiometric mixture of fuel and air inside. In the real world, heat escapes and other materials are present that are warmed by the flame thus reducing its temperature.

 

So, the firm answer is at least 1000C but less than 2000 C above ambient. My SWAG would be roughly 1350C.

 

While we are on the subject of temperatures, the autoignition temperature for av gas is 440 C, for diesel is 230 C and for polyester is 560 C. Motor oil should be similar to diesel. If anyone is interested...

 

Rob