Melting rotor housings
 

Ok so our housing is made out of aluminum, which melts at 1218F. Racingbeat also makes end plates out of aluminum. What confuses me is that our exhaust temps are around 1700F at the header and a even hotter in the combustion chamber. Do you see what I’m getting at. Anyone care to discuss this?

the gasses get that hot, but the plates have water cooling them

i thought about that, but i mean the wall on the inside have to get hotter then 1200 when they are right next to something that is 1700. you would think.

Probably aluminum alloy or something, enough to get it above the 2000 range.

nahh
the metals conduct the heat to the water/oil fast enough to keep from getting very hot

the exhaust gas reads hotter farther away from the
outlet.
if you were to put egt probes in the exhaust stream
you would see lower temp close to the motor and
higher as you move away then as you get farther it
starts to go back down again.
don't believe me try it for your self:)
so what i am saying is that the exhaust temp is not
that high before it leaves the motor.

matt

still buning in the exhaust?

cant tell you why just know what i have seen

matt

The combustion temps aren't 1500F and the actual housing temps inside the engine are surprisingly low. I wish I had some of the old published R&D data mapped out on the engine, but it's quiet surprising. Heat from the turbos has to transfer through water and oil cooled areas that lower the temps substantially.

Sorry for the minor hijack, but what makes the rotary engine run so hot? Its compact size or something? More friction?

Inefficient compared to other power units. Very large combustion surface area as well.

I would swear I read our engines are more efficient than a piston (in the essence of power per displacement).

they do have about 40% less friction than a boinger.

in that way they are, but thermally they are really inefficient (low gas milage) due to the large surface area/low combustion volume, more heat is transfered int the coolant

Ahh I see so an efficient engine would be one that could get rid of the heat instead by exhaust correct? Im guessing the porche boxster engine is really efficient since they use to be air cooled.

30mpg that long ago is pretty good

generally a "normal" piston engine will send about 30% of the conbustion energy out the exhaust, and anther 30% into the coolant, leaving about 30%* to push the pistons down. an engine is considered more efficent when it puts more energy into pushing the piston than heating the exhaust and coolant. rotaries put more heat out the exhaust and into the coolant than the average piston, but theres less friction, and its smaller and stuff

*30% is kinda on the high side....

my 1958 tr3 gets close to 30mpg, and its got a tractor motor, gas mileage has more to do with engine size, speed and # of cylinders, than anything else.

Diesels are in the 40%+ range. Ideally, an engine would not need a cooling system, as if it were 100% efficient, all the energy going into the system, would produce 100% work.

At one time, rotarys did produce more bhp/liter than piston engines. Not so much the case anymore. Toss in the 1.1-2.2 and 1.3-2.6L discussions, and the bhp/L advantage drops even more.

That written, I still love my RX-7!

Just because EGT's are high, doesn't mean your internal engine parts "see" that kinda temps.

Due to coolant cooling (rotor housings) and oil cooling (rotor), the surfaces of these parts will never see even close to what the core EGT's are.

If you don't believe me, pour some water into a styrofoam[sp?] cup.  Put this cup in the middle of a fire.  It's common sense that the cup should easily burn and melt at anything resembling a flame.  So why doesn't the cup melt?


-Ted

i hear you on this, but if you look at the housing cross-section, i think it changes materials just as you get to the peritrochoid. i'm not positive on this, maybe someone could shed some light.

anyway, i also thought that that's why they chrome the housing, not just for a better sealing surface, but also to reflect combustion heat. the rotor turns so fast, even at idle, that the combusted gasses are expelled quickly - out the exhaust - fast enough that the water/coolant will be enough to remove enough of the radiated heat to keep the aluminum from being damaged.

at least ... that's my take.