>>If they burn the same fuel at approximately the same rate per horse
power and have a colder combustion chamber, why is the EGT higher?

So why is it so hot relative to the piston engine?
Robin

I am not sure about this as a reason Robin but the poppet exhaust valve in
a piston
engine transfers some of the exhaust heat to the piston engine cooling
system.
Paul Lamar

David Doshay wrote:

I have another probable explanation, but I cannot be positive either. I'm
just reasoning
the thing out considering the designs of the two engine types.

I think that the difference is how close the exhaust gas is in time with
respect to the
burning phase compared to the power phase.

In both engine designs the engine has extracted as much power as it can
from the fuel
burn, and that is about equal. But in the Rotary there is virtually no time
and no extra
expansion of the gas between the end of the power pulse and the opening of
the exhaust
port. The fuel actually 'pops' out of the exhaust port while finishing
burning. In the piston
engine the piston still moves down a ways, and that expansion undoubtedly
means lots
more cooling just from expansion and also some from contact with the metal
cylinder. I
think expansion is the bigger effect. In addition, still more crank
rotation and time goes
by before the piston pushes the exhaust gas out of that valve opening which
would allow
some additional cooling via contact with the metal engine.

So, I think that in both cases there is a bit of fuel burning after the
power is primarily
extracted from the expanding gas. In the case of the rotary that burning
takes place in
the exhaust pipe but in the piston it takes place at the end of the "power"
stroke after
geometry of the crankshaft is at a good angle for power transfer.

David

 
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