Dose anyone know the actual exhaust temperature of a Renesis engine?

These might give you a rough idea. (http://www.rx8club.com/showthread.php?t=83423&highlight=thermographic)

around 900 - 960 deg C depending on what load the engine is under .

There is a video in one of the threads here of the engine running without the exhaust manifold and it was shooting constant blue flames. That should be pretty damned hot.

Right at the exhaust ports at full throttle you may see 1800*F but 2000*F isn't unheard of. The temps sensor on the cat says much less (around 1650*F or so) but there is a lot of heat lost in the exhaust system over a very short distance.

hot enough on my current tune to turn my custom 20/18 Ga T321 exhaust bright cherry red past the cat, towards where the trans ends, fortunately this cat can take over 1000 degC, Racing Beat claims the OE cat will fry over 1650 degF

the black HPC Extreme ceramic coating I had installed on the manifold has now turned a nice blue hue :Freak_ani

Racing Beat claims the OE cat will fry over 1650 degF

Thats not very good...
:Freak_ani
________
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Thats not very good...
:Freak_ani

What do you want ~~~~~~ You cant expect Mazda(or any auto comapnies) to give us the most super duper uber top of the line CAT for a bone stock car :)

right, they're responsible and impliment pig rich tuning scenarios that eats a hole in your wallet every time you fill up instead :hahano:

I idle at 800°F, cruise at 1200°F and peak at 1680°F measured just before the turbo.

Lets continue. What is the exhaust temp of a piston engine and do the turbos have any issues with the turbine melting in a rotary exhaust?

Piston motors are in the same range, though they tend to run about 200° cooler on average.
Remember - EGT is a relative measure and no two engines are the same.
To melt a turbine would require temps that would have destroyed the motor first.

With my custom exhaust sleeves on a 13B, the very first engine they ever went in had a T-04 on it. The turbine wheel was not inconel. It melted within a few minutes and folded the turbine blades over. The stock 13B exhaust sleeves expand to over double their area within the span of about 2". My sleeves hold the exhaust port shape and area constant and the header pipes are formed to match. They are smaller and higher velocity. I've seen temps of 2000*F with them.

With my custom exhaust sleeves on a 13B, the very first engine they ever went in had a T-04 on it. The turbine wheel was not inconel. It melted within a few minutes and folded the turbine blades over. 316 Stainless steel melts at 2400°F. Aluminum melts at 1220°F.
What was going on there?

Oops. Mistype. I fixed it.

the temperature where steel starts to yield is much lower than the melting temp. It is also dependent on the forces it sees at a given temperature. As the temperature rises the meterial will yield faster for a given temp at doesn't necessary need to be near the melting temp.

Here's a quick chart to illustrate this. I don't know what the typical forces are on a spinning tubine vane but if it's in the 39 to 50K PSI range you could deform a 304 turbine vane at 1300 F.

2. Properties at elevated temperatures
All these values refer to 304 only.
304L values are not given because its strength decreases markedly above 425oC.

Time Elevated Temperature Tensile Strength
Temperature, oF 1112 1292 1472 1652 1832
Tensile Strength, PSI 55130 39171 24663 13057 7254


Creep data Stress for a creep rate of 1% in 10 000 h.
Temperature, oF 1022 1112 1202 1292 1472
Stress, PSI 174093 11606 7254 4352 1451

Since its melting point is 1k°F less than steel, why doesn't aluminum of the rotor housings deform when confronted by 2000°F exhaust temps?

I don't know what the forces or metal surface temps are for the rotor housings. You could probably tell me. I would assume that the housings are cooled by the water jacket so that their surface temp does not reach the plastic region. That and the housings have more surface area than the turbine wheel blades so they distribute the load better. Also based on what I'm hearing from RG and what I know from my turbomachinery experience the hottest gas temps seem to be at the engine outlet. Which must be why they have inconel sleeves on the exhaust ports of the Renisis (understand we aren't talking about it but using it as analogy) but the rotor housing aren't nickel based.

Just to reiterate, my point was to say that you will see deformation of metal before you reach it's melting point based on the forces placed on it and the operating temperature of the metal. It's just physics.

Metallurgy is a blind spot for me.
Its particularly bad when I'm fabricating because I'll just grab any old thing and choose a wire and a shielding gas solely on whether or not a magnet sticks!
Stainless attached to mild attached to zinc-plated...

The apex seal surface is not aluminum, the rotor housing is lined

^^That helps too.:)

MM: I'm not much of a fabricator at all myself, I'm more of a machinist (milling and grinding specifically) who did some design work a long time ago. I have always had great respect for the art of welding and metal forming. Whatever system you have it works and I always appreciate your contributions and knowledge.

Since its melting point is 1k°F less than steel, why doesn't aluminum of the rotor housings deform when confronted by 2000°F exhaust temps?

Heat is constantly being transferred to the cooling system. The hottest spot in the engine is the rotor housings right near the leading spark plug. Surface temps may hit 480*F or so but they don't get much hotter than that as long as there is a cooling system present. There are spots on the rotor itself that can get over 500*F. I've seen engines that have overheated that have had damage in the leading spark plug area. BK Motorsports had 2 such instances during practice for Laguna Seca where they overheated the engine to the point that holes were completely burned through the rotor housings and into the water jacket! This only happens in overheating situations where the heat can not be rejected.

Racing Beat's aluminum side and intermediate housings are all aluminum, including the surfaces. They are nitride coated for wear resistance but that's it. They get all the heat. They don't melt because the cooling system does it's job. On Mazda's factory race peripheral port housings, the intake and exhaust ports are both just aluminum. The exhaust ports get blasted with this heat straight on uncoated aluminum. They don't melt because of the heat rejection from the coolant. Without coolant, the engine will literally melt inside.

I guess there are all kinds of physics going on with the movement of heat.
Cooling system or not, the combustion itself is 1600°F, so there is fluid at that temperature present at the surface of that aluminum.
There must be something in the dynamics of that energy transfer that keeps the aluminum from becoming plastic, despite the actual presence of that kind of heat.

In fabrication, you are above 9000°F , so melting is never an issue - it always happens!

Good information. I was wondering about this because I have been studying the variable geometry turbo in the Turbo 911 as well as models made for diesel engines. All I have read indicates that the additional exhaust temp would make these problematic in the rotary and I did remember RotaryGod talk about the melted turbine. The movable vanning on the 911 seems overly complicated

http://paultan.org/archives/2006/08/16/how-does-variable-turbine-geometry-work/

so I was looking at a diesel design were the vanes do not rotate instead they are stationary and the housing sides up and down the vanes to increase or decrees the intake area. Only one moving part.

http://www.everytime.cummins.com/every/misc/video.jsp?s=broadband

I just wonder if it would be as easy as making the vanes and turbine out of ceramic to eliminate the heat issue. As pointed out the housing will be saved by coolant.

These types of turbos are with out a doubt the future of turbo charging. They do what the 3rd generation RX-7 did with one turbo and a lot less weight and complexity. I would also bet better performance in the end.

I guess there are all kinds of physics going on with the movement of heat.
Cooling system or not, the combustion itself is 1600°F, so there is fluid at that temperature present at the surface of that aluminum.
There must be something in the dynamics of that energy transfer that keeps the aluminum from becoming plastic, despite the actual presence of that kind of heat.

In fabrication, you are above 9000°F , so melting is never an issue - it always happens!


I believe it is the fact that the aluminum is acting like a ferry moving the heat to the coolant never letting enough heat accurate in the metal to cause problems. Take want I say with a grain of salt, it's been a long time since I was sitting in a Thermodynamics class.

I did the variable geometry turbo on my Miata.
It didn't live for long - it doesn't have a wastegate, so it is dependent on metering of the boost signal to control the vanes.
Changes in air density can easily over-spin the thing.

I did the variable geometry turbo on my Miata.
It didn't live for long - it doesn't have a wastegate, so it is dependent on metering of the boost signal to control the vanes.
Changes in air density can easily over-spin the thing.

I can imagine that it would be hard to control but I also think that the integration of a waste gate to control spikes would solve this issue.

I can imagine that it would be hard to control but I also think that the integration of a waste gate to control spikes would solve this issue.You can't integrate a wastegate. That is the problem.
The vanes are controlled with a calibrated actuator inside the turbo. There is no traditional exhaust bypass port.

^^Dude! What is up with that vile avitar!:) Is this how you plan on keeping the kids from stealing from your avatar cookie jar?

When I first saw the variable vane turbo on the new 911T I immediately thought that would be a great match for the rotary. I'm assuming they are using nickel alloys in the turbine section to deal with the heat.

MM what are your thoughts on how Porsche is dealing with the overspin question?

so if we have so much heat, why hasn't the car-b-que become more popular?

When I first saw the variable vane turbo on the new 911T I immediately thought that would be a great match for the rotary. I'm assuming they are using nickel alloys in the turbine section to deal with the heat.

MM what are your thoughts on how Porsche is dealing with the overspin question?

I was thinking the same thing, I still think you could install an external waste gate separate from the turbo to control this but that type of redundancy seems counterproductive. At this point I just don't understand the variable sufficiently to suggest a solution.

MM can you give more details on your Miata set up and what would go wrong and when. You seem to have the most experience here so your the go to guy.

search the news for the guy that caused his car to catch on fire when tried to heat up his lunch :rofl: