Why is Perry running a 24PSI cap??? There are at least two reasons not to run
a high pressure radiator cap. First, the stresses on all the joints in the
system will be higher, causing greater potential for leaks or burst hoses.
Second, the higher pressure will delay the onset of nucleate boiling in the
high heat flux zone of the housing. Nucleate boiling is an extremely
efficient heat transfer regime, and is theoretically what keeps the hottest
part of the engine within reasonable temperature limits. Raising the coolant
pressure may actually raise the hottest metal temperature by forcing the heat
transfer mechanism to stay in the pure forced convection regime until higher
heat flux and higher temperatures are reached.

While I have very limited exposure to third generation engines, I understand
that Mazda may have raised the cooling system pressure. I don't know why they
would have done that. Perhaps to keep from bulk boiling around the
turbocharger after a hot shutdown. Nonetheless, except in racing, the RX-7
will never experience sustained rated power operation, so the cooling system
compromises may be quite different from what is required in an aviation
application.

Jon Lauter
Rotary Power Marine Corporation

 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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