Effects of AFR on EGT, Power

[jeffp]

EGT is universally taken at exhaust flange or port.

<CENSOR BOT DICTATED EDIT> T.I.T. and TOT are a different reading, meant to check turbine efficiency.

 

Now some misguided people will refer to <CENSOR BOT DICTATED EDIT>T.I.T. (Turbine Inlet Temperature) as EGT, and technically it could be called that, but tuning to a temperature at turbine inlet is total folly indeed!

 

EGT is at/in/near the exhaust port as possible by the probes being used. Anthing other is another reading.

 

I know of one person who went from 17:1 to 10:1 puking smoke out of his car and complained he didn't see a change on his EGT Gauge (twin gauge of good reputation and fairly accurate when the thermocouple was checked!)

 

Helps if it was someplace useful, and with an AFR gauge, this engineer didn't have the common sense to realize (like the guys in the SDS article) that the gauges were obviously wrong, and to quit using them and follow the instrument that is tracking the physical symptoms that the engine is displaying!

[jeffp]

I am not obsessed with EGT's really. What I was concerned with at the time, was the temp gauge in the car, and the glowing exhaust turbine housing. That was my indicator my EGT's were getting to high.

The thing is that the engine, EVERY ENGINE, has the sweet spot where it likes to run the best. That is what you are tuning for at the end of the day. To simply setup a fuel map based on what others have done and calling that good is just plain STUPID. As Tony mentioned that may be a good place to start, or it may not, every engine is different, and to be technical, you could tune perfectly one day and the VERY NEXT day have to dial the tune again because of the external variables like humidity, temp, to name two.

 

The fact of the matter is that when you build power you are going to create heat, no matter what you do. True you can run differently with the various fuels that are available, but for the most part, you will run hot.

I don't really care about the EGT's if the engine can sustain that temp long term, and as most of us know the stock high hp L28 can not accomplish this requirement.

 

That is precisely what I have been doing all of my R&D on, to get the heat to a manageable level that I don't melt down my engine in the process of having some fun.

 

The other thing I am going to try is to use an engine dyno, NOT the car dyno. I am wearing out all of my running gear components on the dyno and that isn't good either. I will have the ability to control the engine much better and get a very good tune to run on the dyno, and then check how it has changed in the car. I am really hoping that there will be little difference once in the car. So this is my first go around on the engine dyno, so if it turns out like I believe it will than I will never put my car on the dyno again for tuning purposes.

 

I will have my results here in a few weeks.

[SleeperZ]

On my last set of dyno pulls, this wasn't exactly the behavior that I observed. As I've noted before my setup always seems to have some pretty high EGTs. Running E85 has helped considerably with its inherently lower combustion temps, but I when I tried leaning the mix out a bit, power went up, just as Tony and Jeff observed, but so did my EGTs. Still not as high as they were on gas, but higher none the less.

I don't want to derail an extremely interesting thread, but could you elaborate a bit more on how you run E85? For octane rating or purely for controlling EGTs?

[TimZ]

Lots of replies since the last time I checked...

 

If you look at your EBP and MAP plot, you are running a ratio of less than 1 (EBP to MAP) up to about an RPM of 7000ish. This means your MAP is higher than your EBP. You could easily be getting oxygen in your exhaust during the overlap. The more oxygen there is for oxidation, the longer you can sustain combustion before the oxygen is consumed.

 

By the way, what are you using to measure your EBP? This issue (EBP) has really piqued my curiosity and is causing me to re-evaluate my turbo turbine selection.

I agree - I believe that this is the reason for my elevated Turbine Inlet Temperatures (good point Tony), and why I showed the measured overlap and the TIP readings. This makes sense for my setup which has a relatively huge turbine housing and exhaust, but my understanding was that Jeff's setup uses a much smaller turbine housing for earlier spool. Given that my setup is resulting a bit less than 1:1 MAP/EBP until full boost and then about exactly 1:1, I can't see Jeff's setup having enough blowthrough for it to be the cause of his symptoms.

 

For the EBP I'm using a Ford PowerStroke EBP sensor, connected to the turbine inlet pressure reference through about 8" of steel tubing. They have a measurement range of roughly 18inHg vacuum to 36psi pressure. Actually it works great for a MAP sensor too if you don't pull much vacuum. Do a search on PowerStroke EBP on eBay - you can usually find one for a decent price.

 

What the gist of my post was getting at was NOT the EGT. Jeff seems obsessed by EGT, as do others, but what my point was is that there is no 'magic number' for AFR. People tuning to 11:1 after torque peak likely are running rich and loosing power.

 

The last post from the SDS link is pretty good in that they are saying the same thing I am: Power Output and AFR are what the primary items that dictate tuning of the engine. If the EGT is too high for materials at peak power output, either improve materials, decrease power output, or figure out why it's too high.

 

We were not (at least I wasn't) correlating power to EGT, Jeff didnt like how hot the car was going, and he was trying to tune to someplace in the 1250 range as I recall... But ultimately the result of the days' experimentation was that setting AFR's at some static magic number was only good for a BASELINE TUNE. After that, pulling AFR gave us more power.

 

That it lowered the EGT's IMO is coincidental, but can partially be explained by some of the graphs and charts already posted, all are well rich of Stoich, but running towards a leaner mix resulted in more power after torque peak so like the SDS guys said, 'that's all that matters'.

 

Getting hung on instrumentation readouts may be good for an indepth analysis and ultimately finding out why something happened. But never loose site of the functional result of more power.

 

The thing to take away from my post was that AFR changing after torque peak (pulling fuel) made more power than adding fuel. And that coincided with what the SDS symptoms in their '17:1' example. Regardless of the AFR, once they added fuel and it lost more power, they pulled fuel, and made more power. It's if-then and-or logic when on the dyno. If you get bogged down with what the instruments are saying when the are doing exactly opposite what the power pulls are telling you, then skip the instruments---they're wrong.

 

Most people set or tune to get an AFR like it's a magic goal. "I'm 11:1 and heres' my pull results." The purpose of the dyno is not to tune your car to identical AFR in all the load cels, it's to get the most power under the curve---and that will require different AFRS in each load bin. And I was simply trying to say 'leaner in the upper bins past torque peak' should be something you want to try if you are at 11:1 thinking this is giving you maximum power. Likely, it is not!

 

As you mentioned I was referring to Turbine Inlet Temp as EGT, but as Jeff mentioned I wasn't trying to tune to a "magic number" temp as much as monitoring it and being a bit concerned. Incidentally, I suspect that my Turbine Inlet temp is considerably higher than the EGT at the exhaust port, judging from the condition of the combustion chamber and pistons at the last teardown. The temps I've seen at the turbine inlet would have left obvious evidence on the combustion chambers and pistons, but they looked just fine - not even any oil coking on the underside of the pistons. With this in mind I started with a generic and safe "max power rich" mixture as a baseline and then cautiously leaned out the mix a bit to make more power. I still didn't like seeing the Turbine Inlet Temp going north of 1700F, but it doesn't seem to be causing any actual problems.

 

My main question was regarding the assertion that richer mixtures were the cause of the higher exhaust temps, which didn't make sense to me in this instance and in absence of some other factor. Also, were we just talking about going from 1250F to 1300, or were the temps going higher than that?

 

I don't want to derail an extremely interesting thread, but could you elaborate a bit more on how you run E85? For octane rating or purely for controlling EGTs?

 

I'm assuming you were asking "why" I run E85 - is that correct? More power, 105 octane, lower EGTs, MUCH cleaner burn, usually under $2.50/gallon. Since I've started running it, I REALLY don't want to go back to gasoline.

[Tony D]

Jeff forgets how obsessive he can be at some times... Trust me dude, you were obsessed with EGT's and the number of 1250 for quite a while.

 

Remember we should have had the map done in 45 minutes (in retrospect) but we both got hoooked (obsessed) with doing something else and just kept making run after run...

 

Afterwards we can deny our obsessions, but watching the runs from the 'outside looking in' obsessed sounds like a fair evaluation of the state of mind at the time.

 

The key is to try to not let that happen, keep objectivity, and work using all the information available towards the ultimate goal of power to the ground, and under the curve.

 

That Ford EBP sensor sounds like a neat little gadget, make a nice insturment loop and hook it to an open channel on the MS for a datalogging point. Thanks!

[TimZ]

Jeff forgets how obsessive he can be at some times... Trust me dude, you were obsessed with EGT's and the number of 1250 for quite a while.

 

Remember we should have had the map done in 45 minutes (in retrospect) but we both got hoooked (obsessed) with doing something else and just kept making run after run...

 

Afterwards we can deny our obsessions, but watching the runs from the 'outside looking in' obsessed sounds like a fair evaluation of the state of mind at the time.

 

The key is to try to not let that happen, keep objectivity, and work using all the information available towards the ultimate goal of power to the ground, and under the curve.

 

That Ford EBP sensor sounds like a neat little gadget, make a nice insturment loop and hook it to an open channel on the MS for a datalogging point. Thanks!

 

The EBP sensors work great - I'm actually using one as my MAP sensor too. Just make sure to use a length of steel tubing to connect to the exhaust manifold pressure reference to isolate the sensor from the exhaust temps.

 

...So what was the Turbine Inlet Temp that occurred after making the mixture richer?

[Tony D]

See the EBP unused never installed for $8, or new in box for $89, not bad at all...

My recollection of the results are fuzzy at this point...who knows what happened.

[TimZ]

See the EBP unused never installed for $8, or new in box for $89, not bad at all...

My recollection of the results are fuzzy at this point...who knows what happened.

 

No problem - after seeing that you guys were shooting for 1250F, I'm thinking that my mental model for high turbine inlet temps is different from yours - at this point I'm just happy to keep things under 1600... .

 

...btw - the last build did use custom Ferrea valves built to live under the temps I'm observing at the turbine inlet, and everything is ceramic coated.

Edited February 28, 2010 by TimZ

[Tony D]

Well 1650 for T.I.T. isn't really out there, if you have the valves to handle it, and the turbine wheel is of proper metalurgy.

 

I know our stationary engines which were 'lean burn' natural gas ran 22:1 AFR,s and a consistent 1100F T.I.T., which was identical to the EGT found on the exhaust elbow.

 

T.O.T. would vary, but was usually consistent being it was a stationary, fixed speed, variable load engine. Turbine Delta T was a derivative of the load being applied to the engine. The more load we had, the higher boost we would run, to it's wastegated point, at which point the Turbine Delta would start increasing to it's normal point near full load of 2100KW (which was around 15% overloaded...)

 

When I started looking at Gasoline-Fueled rich burn engines, the difference in EGT was something I had to get used to... the Rich Burn Models of our same engine would be around 800F EGT!!!

[SleeperZ]

I'm assuming you were asking "why" I run E85 - is that correct? More power, 105 octane, lower EGTs, MUCH cleaner burn, usually under $2.50/gallon. Since I've started running it, I REALLY don't want to go back to gasoline.

Makes sense for higher octane. You run it straight or mix it? It must affect your A/F mixtures

quite a bit.

Edited February 28, 2010 by SleeperZ

[ktm]

No problem - after seeing that you guys were shooting for 1250F, I'm thinking that my mental model for high turbine inlet temps is different from yours - at this point I'm just happy to keep things under 1600... .

 

...btw - the last build did use custom Ferrea valves built to live under the temps I'm observing at the turbine inlet, and everything is ceramic coated.

 

My EGT temps are around 1500 to 1600 as well if my EGT thermocouple and LMA-3 are to be believed. I searched extensively on-line and found many, many others running around the same temps. Keep in my mind AFRs are 12 above 15 psi and 12.5 below 15 psi.

 

My actual sensor location is in the exhaust manifold right before the flange where the six runners merge.

Edited February 28, 2010 by ktm

[TimZ]

Well 1650 for T.I.T. isn't really out there, if you have the valves to handle it, and the turbine wheel is of proper metalurgy.

 

I know our stationary engines which were 'lean burn' natural gas ran 22:1 AFR,s and a consistent 1100F T.I.T., which was identical to the EGT found on the exhaust elbow.

 

T.O.T. would vary, but was usually consistent being it was a stationary, fixed speed, variable load engine. Turbine Delta T was a derivative of the load being applied to the engine. The more load we had, the higher boost we would run, to it's wastegated point, at which point the Turbine Delta would start increasing to it's normal point near full load of 2100KW (which was around 15% overloaded...)

 

When I started looking at Gasoline-Fueled rich burn engines, the difference in EGT was something I had to get used to... the Rich Burn Models of our same engine would be around 800F EGT!!!

 

My EGT temps are around 1500 to 1600 as well if my EGT thermocouple and LMA-3 are to be believed. I searched extensively on-line and found many, many others running around the same temps. Keep in my mind AFRs are 12 above 15 psi and 12.5 below 15 psi.

 

My actual sensor location is in the exhaust manifold right before the flange where the six runners merge.

 

Ya - the 1650 was with E85 - I was seeing north of 1800F with gas (Sunoco 94), which did make me a bit nervous.

 

Makes sense for higher octane. You run it straight or mix it? It must affect your A/F mixtures

quite a bit.

 

I run "straight" E85 -no mixing. Actually after having used it for a while now, the only thing that would make it not make sense to run would be if it weren't available. The EFI has been tuned to deliver the proper mixtures for E85 - you have to supply quite a bit more fuel - at max power I'm running an AFR of about 7.2, and at cruise I target around 11. Believe it or not 7.2 is acutally leaner than the max power rich numbers I've seen mentioned - which are usually around 6.95

Edited February 28, 2010 by TimZ

[Tony D]

Yeah, assuming proper thermocouple calibration and instrumentation, 1800 would seem to be a bit high.

 

There is power to be had running on the ragged edge of 'too lean' but it has to be 'worth' the effort. If you are constantly drifting into detonation and beaking things, or burning valves, then is the extra 15-20HP on a 600+ HP car worth it for a non-competition engine?

 

That would be an interesting charting and dyno exercise: Tune to maximum horsepower, REGARDLESS OF EGT. But recording it.

 

Then, using EGT as the basis for further experimentation after the power curve was optimized---go back to retune the engine to a given EGT across the board and see what the power gain/loss was.

 

As you can quickly see without much thinking, tuning to a 'set' EGT accross the board is as ludicrous as tuning to a 'set' AFR----which was the point of the SDS article.

 

EGT is a 'maximum limit' based on components and metallurgy, but nowadays should likely only be used in that fashion and not as an ultimate tuning tool.

 

Curiously I'll chuck this in as well. Our stationary engines ran 1100F. We had Electro-Pneumatic Air Fuel Ratio Control Panels, which the 'lead' mechanic dorked around with to make the engine 'run smoother'---but which resulted in us running 12psi of boost on full load, as compared to the normal 17.5 psig (as a standard inlet manifold temperature of 135F). Within 12 hours of running like this, 12 of the 16 precombusion chambers had been burned out totally---their glowing stinless steel globules deposited on the exhaust valve stellite facings, resulting in 14 of them being burnt (I have two of these valves still in my posession, if you ever stop by the house I can show it to you! )

 

The net result was that by richening the mixture, the internal combustion temperatures went up to a point where things literally started melting. We decreaseed the mass flow of air into the engine, while the gas volume admitted remained the same (cam actuated gas admission valves through an orifice plate), so in that instance 'richer' meant 'hotter' while lean meant cool. But this was an EXTREME case. Like I said, the engines ran at 22:1 AFR in the main combustion chamber, and the precombustion chamber would run around Stoich and blow fire into the main chamber to keep the superlean (low emissions) main chamber burning. If it went the way physics tells us, the precombustion chamber went SUPER rich. I don't recall now if we got T.I.T. or any EGT alarms 'high'---I don't think we did till cylinders started dropping. The EGT monitor we had (by Altronic) monitored all 16 cylinders for EGT high, EGT low, and EGT Differential of more than 100F between all cylinders scanned. It also monitored T.I.T and TOT, but we didn't have alarms setup on that system. The turbo ended up going on that fiasco as well. It was the final straw in the 'lead' mechanic being transferred to another facility and me just being let alone to hotrod those big muthas as I saw fit (made 2500+KW on an 1875KW rated set! WOO HOO! They wondered how I could take a 6 hour maintenance down, but never seemed to impact gross production numbers...muahahaha!)

 

One of the old operators hated me, he would always watch me operate the engines and gas them to full load quickly and start chortling and huffing "Hey man, take it easy! This ain't no Z-Two Eighty!" Ahh, Fat Jack, I wish him ill...