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[PeteH]

It is commonly understood that rotaries have significantly higher EGTs than piston engined cars. I have no specific knowledge either way. But it did lead me to add a calculation for EGTs to my combustion model. Without any particular fiddling I got the following rather interesting result for a stock 231:

EGTs.jpg

The Internet says that EGTs should be kept below 900degC (again, I have no specific knowledge either way, and it does sound like a random number, but I have nothing better). So this turned out to be a far more interesting result than I was expecting. In my model the 231 passes 900degC at about 9500rpm.

For interest, the plots below shows the e-shaft torque, and the actual combustion gas pressure and temperature through the "squeeze and bang" phases of the 4 stroke cycle. These plots are at 5500rpm (peak torque), and with the ignition timing set to 33deg (which I identified as MBT):

Torque.jpg

Pressure.jpg

Temperature.jpg

In case you are wondering, the mean torque over the cycle is 219Nm.

[13Black]

But what about the random number to convert gas mass to EGT

I spotted 270 degree stroke, good boi. Scrooby snacc for Pete.

I recall Racing Beat saying something about EGTs in that region being some sort of safe max. How this was derived, I'm not sure.
I would assume that their measurements were in the manifold and would be a smidge cooler than the theoretical max.
I've been meaning to get a usable EGT setup but so far, not much joy. Latency and the lack of steady state conditions have made previous attempts a waste of time.

[PeteH]

Latency and the lack of steady state conditions have made previous attempts a waste of time.

You or the car?

I am planning to fit EGT sensors to the 20B. I think I'll need all the help I can get to try to keep it in one piece.

It seems to me that while the engine is efficient, and combusting well, the EGTs will follow a clear linear trend that is weakly related to the revs. When it starts to breath badly, or if the timing is wrong, or the AFRs are wrong, then the EGTs can climb. So I think the EGTs should be a very good indication of the health of the tune. And they will give a clear indication of at what revs it becomes necessary to richen up the mixture to protect the engine.

[13Black]

Are there any controls in your ECU options to use EGT as a feedback loop?
I.e if EGT exceeds x by y, increase injector duty by y*z

[PeteH]

I haven't bought it yet, but the one I'm looking at has 4D tuning tables, and can use EGT as one of those tables. So yes.

[warpc0il]

My old Alfa has two twin-choke Weber DCOE carbs, that can be a bugger to synchronise, with the cable operating an adjustable linkage between them.

After the last carb "strip, clean and rebuild" I couldn't find my mercury vacuum tube adaptors that I would normally use, so had to "balance them by ear", just listening to the engine as I adjusted the linkage.

It occurred to me that I had an IR gun thermometer and could use that to check the EGT on the 4-branch exhaust manifold.

With the carbs set to what I sensed as "balanced" the EGT's were within 5°C of each other, tracking between 285°C and 350°C between idle and fast idle.
When a replacement set of adaptors arrived, the mercury gauge confirmed that I had got the balance within a gnats.
Out of curiosity, I then set the balance off, just to see if the EGT was a valid indicator and was amazed how little offset in the carbs would make a significant difference in header temps, easily 30°C and with a noticeable lag in between slow and fast idle.
Back to "balanced" and all was good.

While the actual numbers don't mean much when compared to a rotary, and my exercise was low-speed, no-load, it does still go to show that individual EGTs are very much dependant on the load and combustion conditions of each cylinder.

While the Renesis has no means to "balance" or "unbalance" the load between the two rotors, I've often thought that having real-time measurement of the EGT's would be a good early indicator of something going wrong, be that a fuel injector, ignition or compression.

A significant difference in EGT wouldn't show what was wrong, just that something wasn't right.

This is what we used to do on twins and latter multi-cylinder bikes with chrome exhaust headers, where you could tell from the "blueing" of the headers if one cylinder was working harder or less hard than the others.

BTW In case anyone is wondering, you can type a "°" (degrees symbol) on a Windows PC by holding the ALT key down and hitting 0176 on the keypad, or you can use "%windir%\system32\charmap.exe" if you can't remember all the codes.

[qwakers]

or (with win10) just press windows key and type charmap and it 'suggests' the character map in the start menu

[PeteH]

(All of which take more keystrokes than typing 'deg' )

[13Black]

I just use an apostrophe. I like to think of it as me making up for other people not using them where they should.

[RenesisRaceBuggy]

I could always tell when I'd gone too far with the idle control pulling timing on the Renny* as the exhaust manifold would suddenly get noticably hotter just stood near it, it's an underrated tuning tool even without sensors.


*Like most race cars it ran the throttle open pretty far and the timing pulled back so it was actually firing ATDC when it was hot to pull the idle down - gives a much smoother transition from idle and faster throttle response, and lets you use the advance for cold/hot idle compensations instead of a relatively slow ICV - which is more weight and another failure point. And the extra air and fuel warmed things up faster while driving to the stage start.

[Ainmhidh]

(All of which take more keystrokes than typing 'deg' )

hold right-alt and press zero on a Mac... º

[13Black]

52875405_2093083850740482_1223350193643061248_n.jpg

[PeteH]

There, that's sorted.

(Now, I've been meaning to do something on exhaust gas temperatures, but I'm not sure it will capture the zeitgeist quite like this thread has)

[350matt]

hold down alt and type 0176 = °