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In a message dated 12/5/2007 10:17:51 AM Eastern Standard Time, wrjjrs@aol.com writes:
Ed, intake charge cooling is fairly easily understood, but I believe Ben was talking about cooling the rotary EXHAUST. You have mentioned that the exhaust tends to melt or batter everything in front of it.
Bill Jepson
The problem with the big HP numbers with any of the smaller engines, is that the smaller and lighter they are the more difficult it will be to remove the waste heat. Just not enough engine internal surface can be exposed to the coolant. Once the mass has heat soaked to near its limit, things start changing shape, and getting soft and weak.
There are dyno shops around the country where the kids meet to race. The water injection tricks are used, along side the big K&K turbos to produce 600+ HP on the chassis dyno.
Both piston and rotary engines can do this magic for the whole length of a dyno pass.
About 15 seconds.
So engine B can flash 450 HP on a dyno pass. How long can it produce 450 HP before a major problem developes? Maybe 30 seconds? three minutes?
The actual amount of power that can be recovered over a long period of time is then a much lower figure. Perhaps 220 HP from a two rotor with a very good cooling system layout.
The propeller that could absorb even 400 HP would be a poor match for 220 HP after take off. So if the available power is not continous power, it is just about not usable anyway.
You may notice the CO2 nozzles pointing at the engine compartment and floor of the dyno cell. They are seldome needed for rotary engined cars. When a rotary has a catastrophic failure, it may even keep running with a bit of power. They very seldom lock up like a piston engine. I have had to cut the heads off of the case bolts to get one apart. You have no doubt about a failure when you find yourself doing this. But no oil had been liberated during the failure.
Not the case with a piston engine. In fact it is seldom that a piston engine has a massive failure without at least a small oil fire, and often with a very big oil fire. So the CO2 nozzles, should the many pieces inside a screaming turbo Toyota be liberated unannounced.
Another point for the rotary.
The high EGTs of the rotary are a common complaint. In the steady state performance required of an airplane engine, the exhaust system will reach, and stay at a very high number. But best power will be below 1,700 degrees, and leaned to best cruise could be below 1,600 degrees. The same plane with a piston engine might see 1375 to 1425 degrees. In both cases stainless tubing holds up well. With a bit of cooling air it would have a long life as well. The shock waves in the exhaust flow are a real problem. Muffler designs must be robust to remain assembled at all. Shapes that do not emulate pressure vessles do not survive for long.
My friend landed his Tripacer on fire after a swallowed valve and a massive hole in the case. The windscreen covered in oil and a cabin full of smoke. His wife called out a farmers private airstrip just ahead, and an uneventfull landing was made. The fire went out when it ran out of oil. Just an engine failure, is not the worst thing that can happen.
The only stainless in the race car exhaust system is in the giant Borla muffler. The headers are .145" wall mild steel with an air supply to cool them. Never a problem.
Lynn E. Hanover
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