Effect of Timing and Air Fuel Ratios on EGT

[jdub]

Began a new thread to avoid hijack of the "MPG on 550's" thread...since this is a discussion of the effect of timing and/or AFR on EGT. Here's the beginning of the discussion...I'll enter the copied thread post by post for clarity.

Forgive me if I'm mistaken but aren't you the guy who recently claimed A/F ratios have no effect on EGT? Did your BSAT teach you that too?

Yup I did.. and yes.. it did. I don't think I said "no effect", however.

EGT's are mostly influenced by timing. You start to see this phenomenon when you deal with a standalone.

You ask.. why do my EGT's skyrocket when I lean my car out?

EGT's skyrocket due to timing being pulled. When you lean out the car too much, you start setting off the knock sensors. When the knock sensors.. sense knock, they tell the ECU to pull timing in order to save the pistons.

When timing is pulled (spark plug ignited later combustion stroke) you start introducing heat (due to ignition of air and fuel) later in the combustion cycle. Thus... EGT's rise.

If you want to see this yourself. Set your car to 0 degrees BTDC. You'll see 100C higher temps on your EGT guage. I drove for 130 miles this way on a new motor. Same air fuel ratios, just some retard set the retarded timing.

 

[jdub]

My response:

retarding igntion timing will greatly effect EGT. Really.. a/f isn't an influence in EGT. The reason why people will see higher EGTs when leaning a car is due to the car seeing knock, and retarding the timing. WHen it pulls timing, EGT's riase.

EGT's are raised due to the point at which the heat is released in the combustion cycle. It is released later and later, and eventually, the exhuast will be open when heat is released (I'm being very simplictic here). EGT's and air to fuel ratios.. really have no correlation.

This is what you actually said Alan

Yup I did.. and yes.. it did. I don't think I said "no effect", however.

EGT's are mostly influenced by timing. You start to see this phenomenon when you deal with a standalone.

You ask.. why do my EGT's skyrocket when I lean my car out?

EGT's skyrocket due to timing being pulled. When you lean out the car too much, you start setting off the knock sensors. When the knock sensors.. sense knock, they tell the ECU to pull timing in order to save the pistons.

When timing is pulled (spark plug ignited later combustion stroke) you start introducing heat (due to ignition of air and fuel) later in the combustion cycle. Thus... EGT's rise.

If you want to see this yourself. Set your car to 0 degrees BTDC. You'll see 100C higher temps on your EGT guage. I drove for 130 miles this way on a new motor. Same air fuel ratios, just some retard set the retarded timing.

I'm not sure where you get this from, but the knock sensors will not pull timing until they detect knock...leaning the mixture out will not necessarily cause knock as you alluded to in the FP/550 discussion. So explain what happens below WOT...say at 75% throttle. Is the ECU gonna pull timing due to knock? EGT's are not gonna go up due to leaning fuel out?

AFR greatly affect EGT...how do I know that? In piston powered airplane there is a red mixture knob...a control pilots are taught very early to respect. We set cruise mixture to get the best "MPG" by setting this knob using EGT as a reference. Mess this up and you'll be finding yourself a place to land pretty darn fast...there's more than one "smoking hole" out there due to leaning the motor, making EGT go through the roof.

There are no knock control systems in a piston aircraft...timing is fixed. EGT is the primary method to set power and economy (fuel flow). The engine is run typically above 75% for hours...100% for takeoff or go around. You manually adjust the mixture according to EGT...you can go to zero fuel (that's how you shut the engine down) to 100% fuel...complete control over the mixture. There is no ECU, no O2 sensor...the pilot is the ECU

Not too sure what school you went to, but pilots (and I am one) know a great deal about this...AFR has a far greater impact on EGT than timing ever will.

 

[jdub]

Alan's Response:

This is what you actually said Alan

Ya. That's it. Thanks for reinforcing my thoughts with an earlier post.

I'm not sure where you get this from, but the knock sensors will not pull timing until they detect knock...leaning the mixture out will not necessarily cause knock as you alluded to in the FP/550 discussion. So explain what happens below WOT...say at 75% throttle. Is the ECU gonna pull timing due to knock? EGT's are not gonna go up due to leaning fuel out?

Leaning the mixture will not always cause knock.. depends on where you start leaning it from. If you continue leaning, preignition (pinging) happens and the knock sensor pulls timing.

I get this from tuning an AEM on a talon for a three hours in addition to *weekends* spent with another AEM owner getting his car just right. I get this from a 4 year automotive degree from a NAIT (national association for industrial technology) accredited university. I get it from my own experiences.

I *CHALLENGE* you to do this. Set your timing to 0 degree BTDC. Drive the car at cruise on the highway at 80mph. Look at your EGT's. My greddy guage told me I was seeing 750C(ish) at the collector. Normally I'd see 600ish. I drove a round trip of 140 some miles that day. No damage to the car.

Do this.. and get back to me. Tell me that EGT's aren't influenced by timing.

AFR greatly affect EGT...how do I know that? In piston powered airplane there is a red mixture knob...a control pilots are taught very early to respect. We set cruise mixture to get the best "MPG" by setting this knob using EGT as a reference. Mess this up and you'll be finding yourself a place to land pretty darn fast...there's more than one "smoking hole" out there due to leaning the motor, making EGT go through the roof.

So.. leaning out by 5% across the board shows a difference on the egt guage? How much of a difference? 10%? How much hotter does 10% get you?

Didn't you bring up comapre apples to apples?? An aircraft that travels at 10k feet above ground compared to some a car that travels on the ground.

There are no knock control systems in a piston aircraft...timing is fixed. EGT is the primary method to set power and economy (fuel flow). The engine is run typically above 75% for hours...100% for takeoff or go around. You manually adjust the mixture according to EGT...you can go to zero fuel (that's how you shut the engine down) to 100% fuel...complete control over the mixture. There is no ECU, no O2 sensor...the pilot is the ECU

I don't know much if anything about aircraft motors.. so I can't comment on this. How much resolution does this EGT have?

Not too sure what school you went to, but pilots (and I am one) know a great deal about this...AFR has a far greater impact on EGT than timing ever will.

I used to think that EGTs were influenced by air/fuel ratios. I was on a forum started by Corky Bell many years ago (even have an autographed copy of Maximum Boost by him ). He was the one that explained it to me years ago. I didn't believe him and questioned it further. He was very technical in his explanation. It took me a while to see it, but eventualy I did. All of this was further reinforced by my personal experiences on a dyno and aem time.

 

[jdub]

Thread is up-to-date:

Ya. That's it. Thanks for reinforcing my thoughts with an earlier post.

Yes you did and the point being is the statement "EGT's and air to fuel ratios.. really have no correlation." and "EGT's are mostly influenced by timing."

That's just plain wrong...it's making a statement in a very black/white manner. When in fact the AF ratio has a great effect on EGT compared to timing when the engine is set in the normal timing range.

Leaning the mixture will not always cause knock.. depends on where you start leaning it from. If you continue leaning, preignition (pinging) happens and the knock sensor pulls timing.

I get this from tuning an AEM on a talon for a three hours in addition to *weekends* spent with another AEM owner getting his car just right. I get this from a 4 year automotive degree from a NAIT (national association for industrial technology) accredited university. I get it from my own experiences.

I *CHALLENGE* you to do this. Set your timing to 0 degree BTDC. Drive the car at cruise on the highway at 80mph. Look at your EGT's. My greddy guage told me I was seeing 750C(ish) at the collector. Normally I'd see 600ish. I drove a round trip of 140 some miles that day. No damage to the car.

Do this.. and get back to me. Tell me that EGT's aren't influenced by timing.

I never said timing has no effect on EGT...not once. But, you did say AF ratios "really have no correlation"...I'm not dealing with or making statements based on absolutes.

You are basing your assertion on the knock sensors pulling timing...now you say leaning doesn't always cause knock. What happens to EGT when the motor is leaned out, but not enough to activate the knock sensors? You kinda side stepped this question Alan...it's fairly obvious EGT will increase.

I don't have to do this...anyone who has installed a CPS one tooth off and has an EGT gauge can attest to what happens...EGT will go up. But your trying to say AF ratios has no effect...so, (since you have an AFC) lean the mixture down and watch what happens or make it pig rich at 3000 rpm and watch your cylinder temps drop a 100 deg C.

On a properly timed motor with valve timing set correctly (0 degree BTDC is not normal), the effect of moving the timing in the normal range or the effect of the knock sensors pulling timing (the table the ECU uses is in the valve timing range) will not have near the effect you describe above. Also, with an AEM EMS (which few MK III owners have), you can set the parameters for the injectors, timing, etc just about anyway you wish...my experience tells me (both in aircraft and with the 7M) that AFR will affect EGT.

So.. leaning out by 5% across the board shows a difference on the egt guage? How much of a difference? 10%? How much hotter does 10% get you?

Didn't you bring up comapre apples to apples?? An aircraft that travels at 10k feet above ground compared to some a car that travels on the ground.

I don't know much if anything about aircraft motors.. so I can't comment on this. How much resolution does this EGT have?

You see 100-200 deg swings on an aircraft engine, depending on throttle and mixture setting...they are designed to operate from sea level to the service ceiling of the aircraft. In the airport traffic pattern, the pilot goes rich on the mixture due to the constantly changing throttle setting...leaning the mixture out in the pattern is asking for engine failure. At cruise is where setting EGT comes into play...you normally climb at 100% throttle. At level off, you pull the throttle to 75% or so...EGT drops just as coming off WOT on the 7M. Then you set the mixture, leaning the engine for max fuel economy...EGT will increase as a result. Understanding what the mixture does is one of the basics in flying piston powered aircraft.

Most light aircraft fly around at 5,000' above sea level or less in my neck of the woods...takes too much fuel to climb higher for little gain in economy. I do believe Denver is about 5,000' and quite a few members on this board live there and drive their cars in the mountains
Sounds like the comparison is valid to me...at least from an operating environment stand point.

Aircraft engines are built to a much higher standard than a puny 7M...they have to be. The HP power to weight of the motor is impressive...many aircraft engines are turbocharged as well to achieve performance at high altitude. The instrumentation is at a much higher standard than automotive...the FAA requires extensive testing of all aircraft components and the engine requires inspection/overhaul at specific hour intervals. Using automotive components in an aircraft engine is a big no, no.

I used to think that EGTs were influenced by air/fuel ratios. I was on a forum started by Corky Bell many years ago (even have an autographed copy of Maximum Boost by him :icon_bigg ). He was the one that explained it to me years ago. I didn't believe him and questioned it further. He was very technical in his explanation. It took me a while to see it, but eventualy I did. All of this was further reinforced by my personal experiences on a dyno and aem time.

I'd like to see it. Like I said, I do know timing affects EGT...I also know AFR does too...any pilot will tell you that and it's proven with thousands of hours flown daily...FAA approved training courses incorporate it as basic knowledge. And as long the timing is in the normal range for the engine, I'm pretty convinced AFR will have the greater effect on EGT.

 

[Nick M]

"Lean is mean" is a correct cliche' from racers. The more heat you extract from combustion, the more power you produce. And the exhaust temps go up.

Another thought on it. EGT and combustion temps, those are two different things, but of course are related.

I just thought of something else with jdubs post. The type of fuel used. Different ratios may yield different results with different fuel. JP8 does not burn like gasoline obviously.

 

[jdub]

Small piston aircraft use 100 Octane low lead

And you are correct on the cylinder temps being not the same as EGT...there is (as you noted) a direct correlation.

 

[starscream5000]

If you run pig rich in your A/F's won't it cool the EGT's due to the extra fuel cooling it? And if you lean it out too much, won't the extra air also lower EGT's? If that's true, then this guys statements are kinda moot when saying timing affects EGT's more....:nono:

 

[Nick M]

If you run pig rich in your A/F's won't it cool the EGT's due to the extra fuel cooling it? And if you lean it out too much, won't the extra air also lower EGT's? If that's true, then this guys statements are kinda moot when saying timing affects EGT's more....:nono:

Because exhaust gas is just that. And combustion is what happens inside the cylinder. If you delay the starting point of combustion by retarding the ignition, it will not burn as hot, but the will heat will transfer into the exhaust manifold when that valve opens.

Retarding timing can lower combustion temps, but raise EGT's.

What Jdub is saying about AF ratio's is correct.

 

[starscream5000]

Ok I see now. Thanks!

 

[dav_dman]

i lowered the egt temp on my two stroke engine by raising timing, to a point. There is no knock sensor..either i get it right or i deto into meltdown.

I also lowered my egt richening the mixture, but again, only to a point. I did it, i measured it, i saw it.

both affect combustion temp, as does dome design and squish band.

 

[MDCmotorsports]

Im with Al on this one...

 

[aljordan]

Thread is up-to-date:

Yes you did and the point being is the statement "EGT's and air to fuel ratios.. really have no correlation." and "EGT's are mostly influenced by timing."

That's just plain wrong...it's making a statement in a very black/white manner. When in fact the AF ratio has a great effect on EGT compared to timing when the engine is set in the normal timing range.

AF has SOME effect on egt (note my use of the words mostly and highly, ect) . Obviously it has an effect. You start at 10-1 a/f and go to 11-1 (not to the point where the knock sensors are tripped) you'll see hotter temps. If you start at 10-1 and go to 11-1 AND you get to the point where you introduce knock (knock sensors pull timing), you'll see MUCH higher temperatures.

Define normal timing range. A motor where timing isn't being pulled by the knock sensors? Or a motor that's static timing is correctly set? If you say both.. my agrument is moot as timing being pulled effects egt to a higher and greater degree compared to a/f was my agrgument.

I still say that you need to try my challenge. You'll see a/f ratios are the same, yet egts are 150C above normal. The only change would be static timing. Which is when the plug ingnites the mixutre.

I never said timing has no effect on EGT...not once. But, you did say AF ratios "really have no correlation"...I'm not dealing with or making statements based on absolutes.

I used the term really in an Indiana context. Sorry about that. I should have used the term "hardly have any correlation".

You are basing your assertion on the knock sensors pulling timing...now you say leaning doesn't always cause knock. What happens to EGT when the motor is leaned out, but not enough to activate the knock sensors? You kinda side stepped this question Alan...it's fairly obvious EGT will increase.

Leaning doesn't always cause knock. leaning from 10 to 11.5 on a wideband shouldn't (altho it may) introduce knock. Leaning from 11 to 12.5 would very likely introduce knock. EGT will increase, but to a lesser degree compared to that of timing being pulled. Say 50C by leaning comapred to 200C with timing being pulled. The delta is much greater with the latter.

I don't have to do this...anyone who has installed a CPS one tooth off and has an EGT gauge can attest to what happens...EGT will go up. But your trying to say AF ratios has no effect...so, (since you have an AFC) lean the mixture down and watch what happens or make it pig rich at 3000 rpm and watch your cylinder temps drop a 100 deg C.

I don't beleive that I've never said "no effect". My agrument was that timing is a much greater influence on EGTs when compared to a/f.

On a properly timed motor with valve timing set correctly (0 degree BTDC is not normal), the effect of moving the timing in the normal range or the effect of the knock sensors pulling timing (the table the ECU uses is in the valve timing range) will not have near the effect you describe above. Also, with an AEM EMS (which few MK III owners have), you can set the parameters for the injectors, timing, etc just about anyway you wish...my experience tells me (both in aircraft and with the 7M) that AFR will affect EGT.

0 BTDC is NOT valve timing. I'm not talking valve timing in this.. I'm talking about static timing. The point at which the plug is fired. I'm sure you just made a typo. At least I hope you weren't thinking of valve timing the entire time.

I know very few mk3 owners have an AEM. I'm lucky enough to have a good friend who has one, and who is doing extremely well with it. I keep bring up an AEM for the VERY reason that you can adjust parameters seperate of others. Such as puling back timing, yet keeping a/f the same. A deffinate NOTICEABLE (100C<) increase in EGTs will result.

As I've always stated... timing will have a greater (I've used greatly and mostly in the past) influence on egts compared to a/f ratio.

You see 100-200 deg swings on an aircraft engine, depending on throttle and mixture setting...they are designed to operate from sea level to the service ceiling of the aircraft. In the airport traffic pattern, the pilot goes rich on the mixture due to the constantly changing throttle setting...leaning the mixture out in the pattern is asking for engine failure. At cruise is where setting EGT comes into play...you normally climb at 100% throttle. At level off, you pull the throttle to 75% or so...EGT drops just as coming off WOT on the 7M. Then you set the mixture, leaning the engine for max fuel economy...EGT will increase as a result. Understanding what the mixture does is one of the basics in flying piston powered aircraft.

I'm guessing that 100-200 is Fahrenheit and not Celcuis. 100F is only 38C and 200F is 93C. A swing of 100C is certialy possible when leaning out a motor, however, timing will have a GREATER change such as 200C+(392F).

Most light aircraft fly around at 5,000' above sea level or less in my neck of the woods...takes too much fuel to climb higher for little gain in economy. I do believe Denver is about 5,000' and quite a few members on this board live there and drive their cars in the mountains
Sounds like the comparison is valid to me...at least from an operating environment stand point.

What about the guys who fly in Denver? I don't know if a fixed timing motor with antiquated (as it seems) engine controls rivals that of a motor which has on the fly timing adjustment (knock sensors).

Aircraft engines are built to a much higher standard than a puny 7M...they have to be. The HP power to weight of the motor is impressive...many aircraft engines are turbocharged as well to achieve performance at high altitude. The instrumentation is at a much higher standard than automotive...the FAA requires extensive testing of all aircraft components and the engine requires inspection/overhaul at specific hour intervals. Using automotive components in an aircraft engine is a big no, no.

"The HP to weight of the motor is impressive.." you're not comparing the weight of the motor.. to it's hp output are you? My 7m is near 1hp her pound if that's the case.

I believe they are turbocharged so they can get some oxygen to burn. O2 is few and far between comapred to what we see at sea level. Forcing in 2 atmospheres effectively doubles the amount of o2 in each gulp.

I'd like to see it. Like I said, I do know timing affects EGT...I also know AFR does too...any pilot will tell you that and it's proven with thousands of hours flown daily...FAA approved training courses incorporate it as basic knowledge. And as long the timing is in the normal range for the engine, I'm pretty convinced AFR will have the greater effect on EGT.

Again... my ENTIRE argument is that timing influeces egt to a MUCh GREATER degree compared to a/f ratio. I've tried to reiterate this throughout this entire thread.

 

[donnys90T]

You're wrong. Aircraft and auto technology may be apples to oranges but combustion theory remains identical. I'm surprised this issue is even being debated because it's so basic. Unless there is some sort of misunderstanding here you need to get your money back from whatever school you went to.

Of course if you changed timing to a great extent it'll have a great effect on egt but if we're going to stick with your example the maximum correction in a knocking 7M can never be more than 10 degrees. In that context a/f ratio would have a far greater effect. It all comes down to how much of a change in either you're talking about but since a/f ratio is directly proportional to fuel it's effect on egt will be more pronounced over the range timing is changed during knock correction.

Look, we're off on a tangent. This entire thing started because you said this:

"EGT's and air to fuel ratios...really have no correlation."

That's just wrong. If you had experienece operating an engine that comes standard with instrumentation displaying EGT and CHT for all cylinders, along with fuel flow, an engine that offers full manual control of mixture, you'd know that's nonsense. If you didn't mean to say that you should have chosen your words more carefully

Here's a question for you: Fir any given a/f ratio if you had two plugs in the same cylinder firing at the same time and you shut one plug off what will egt do? Rise, fall, or stay the same? And why?

 

[aljordan]

donny and jdub. I misstyped "EGT's and a/f ratios.. really have no correlation". My bad. However, this this entire god damn thread.. I've said "influences heavily", "mostly", and "greatly". These words are not aboslutes.

Sure a/f can change egt. But not *near* as much as timing. This is my argument. Always has been.

If EGT is so highly influenced by a/f, then why even bother with a wideband?

I know what I know by experience, backed up by theory, and backed up one of the more well known tuners in the US. Not much more I can cover.

To answer your question donny... it wouldn't change. Adding (or subtracting) an ignition source should not change burn temps of the fuel charge. Only way to change burn temps would be to introduce more combustable material. Would be similar to starting a fire in 2 spots of a piece of paper, measuring the temps of each fire, then measure the temp as they join to become one. Same terperature since the same combustable material is being burnt.

 

[donnys90T]

"If EGT is so highly influenced by a/f, then why even bother with a wideband?"

EGT is used by many in the automotive field for monitoring A/F ratios and as the other poster pointed out several times it's the only way power is set in aircraft. WB is used because it responds faster. You must be a young fellow because the WB sensor is a recent invention. What do you think was used for tuning A/F ratio prior to them?

"To answer your question donny... it wouldn't change."

Incorrect. EGT will increase and for good reason. Again, ask any pilot. Looking specifically for an increase in EGT is how each portion of the dual ingition system used in aircraft is checked. The same thing would occur in any 4 cycle gasoline powered engine using dual ignition. Sorry guy but its hard to buy into what you're pushing when you keep demonstrating an ignorance of basic combustion theory. I suggest a study of flame front and its propagation.

 

[aljordan]

EGT is used by many in the automotive field for monitoring A/F ratios and as the other poster pointed out several times it's the only way power is set in aircraft. WB is used because it responds faster. You must be a young fellow because the WB sensor is a recent invention. What do you think was used for tuning A/F ratio prior to them?

So what temperare equates to what temperature reading? Why use a wideband while a simple and much cheaper narrow band sensor will tell us quickly if we're rich or lean. Since EGT can be used to see a/f ratios this seems usesless.

Incorrect. EGT will increase and for good reason. Again, ask any pilot. Looking specifically for an increase in EGT is how each portion of the dual ingition system used in aircraft is checked. The same thing would occur in any 4 cycle gasoline powered engine using dual ignition. Sorry guy but its hard to buy into what you're pushing when you keep demonstrating an ignorance of basic combustion theory. I suggest a study of flame front and its propagation.

For good reason???? WHAT IS THAT REASON?? Since you understand things.. let us all know.

 

[jdub]

Normal timing range of the Toyota TCCS starts with base timing set at 10 deg BDTC. Under normal operation (ECU not in diagnostic, fail safe, or back-up mode) the TCCS utilizes a spark advance based on a look-up table in the ECU. This spark advance map covers any combination of engine speed, load, coolant temperature and throttle position. The knock sensors adjust for variances in fuel octane...to prevent engine knock...the knock sensors (as Donny correctly stated) will not pull timing more than 10 degrees. This is what I mean by normal timing range or conditions.

Under these conditions, retarding timing to the degree you state Alan is not possible...unless you are using a stand alone or some other electronic piggyback to do so. However, if you severely retard base timing by setting the CPS off by a tooth...well, that will cause EGTs to shoot up. But this is not a normal condition of the engine or the TCCS.

The primary purpose of the TCCS is to keep timing, AFR, rpm, etc in balance. It is almost impossible to change one without inducing a change in another. That is why I used light aircraft engines as the example...the engines are not archaic Alan...they are designed to be simple for a reason. Simple means less failures (remember the KISS principle?)...use of an EMS on these may cause the motor to perform in a way unexpected to the pilot. Keep in mind many of these light airplanes are used to train new pilots...a task much more complicated than driving a car. A motor based on simple operating principles is good

This is why it is very easy to see the effect of mixture on EGT. You don't have an EMS changing anything else. In an airplane piston engine at cruise (75% throttle) you can run at peak EGT, rich of peak, or lean of peak. 200 deg F on the rich side yields best power and highest cylinder head temps, peak EGT yields best economy for the speed, and lean of peak yields even greater economy along with a cooler and cleaner running engine. Power drop and roughness occurs at about 100-150 deg F on the lean side of peak. At 75% throttle you can't damage the engine by leaning it out (you can make it run rough or cut off though) and the same applies to car engines...knock/detonation is not going to occur at 75% throttle. The point here is you are changing EGT 100 to 200 deg F by adjusting the mixture alone and the difference in change for deg C is very close at the temps we are talking about (see below)

Might want to check your C to F temp conversion It depends on the temperature range you're looking at...you have to convert the low C temp vs the high C temp both to F and take the difference. For example: 700 deg C = 1292 deg F....600 deg C = 1112 deg F. The difference in temp is 180 deg F for that scale.

As Donny pointed out, the design of aircraft piston engines and automotive engines are far different, but the principles they run on are identical. Turbos are used in aircraft engines for the same reason as in an automotive engine...to produce more power. This is an advantage to airplanes due to the higher altitudes...it's the same advantage in a Supra being run in the mountains at 7,000' vs a NA engine. The ability of an aircraft to achieve higher altitudes is moot in this discussion.

Edit: C to F temp conversion for accuracy

 

[aljordan]

I'm not going round and round on this discussion. I have more important things to do than battle this trivial bullshit.

I'm heading over to piperforums to read up on toyota TCCS operation.

FYI, your C to F calc is fucked up. "Google 700 c to F" and you'll see 1292F.

 

[jdub]

FYI, your C to F calc is fucked up. "Google 700 c to F" and you'll see 1292F.

Yeah...you're right...that's what I get for doing it in my head
I guess the temp difference is actually 180 deg F for an increase of 600-700 deg C.

 

[donnys90T]

Knowledge is never trivial.

I'm assuming you're asking what EGT temperatures equate to what A/F ratios. The above poster has it correct. Peak EGT occurs at sotichiometric while best power can be found about 200 degrees on the rich side of peak.

To answer your other questions I'm sure you already know a narrowband sensor isn't effective on either side of stoichiometric so it's useless for accurate tuning of A/F. An EGT probe isn't as fast as a wideband but it was all we had not long ago. It still has it's place for measuring such things as turbine inlet temperature on a turbocharger and remains a much more accurate way of setting A/F ratio when the engine is operated at the fairly constant power settings used in some forms of racing. This type of operation negates the EGT's slightly slower response time but even with it EGT remains a good back up for street use because of it's close correlation with A/F ratio.

Other points: auto engines are computer controlled while most aircraft engines are manually controlled. In an airplane engine operating at 75% power EGT settings can be approached from the rich, or "safe" side. That's more difficult to do with an ECU controlled mixture in cars. Another difference is aircraft engines are operated at constant power settings while auto engines are generally not. Why don't aircraft use WB sensors? Because EGT is a far more accurate method of determining air fuel ratio than measuring O2 in the exhaust. Lambda is an indirect indication of A/F ratio while EGT is direct. I keep telling you that but you refuse to listen.

Why does EGT rise when one plug is disabled in a dual ignition system? Two plugs in one cylinder are obviously not going to be mounted next to each other. What would be the point? Dual ignition is not only used to provide redundancy. It's used to insure equal flame front propagation which produces many benefits. I remind you combustion is not an explosion. It's a controlled burn.

One plug is placed at an angle on one side of the cylinder head while the other plug is placed at the same angle on the other side. The two plugs ignite the air/fuel charge simultaneously and the flame front propagates outward from each plug. If one plug fails to fire the flame front burns across the cylinder. In such a case it should be obvious more time is required for full combustion to take place.

Since valve timing remains unchanged when the exhaust valve opens the air/fuel charge that hasn't been fully consumed (or only recently consumed and hasn't had time to cool compared to when both plugs ignited it) passes into the exhaust system. The result is an increase in EGT on the order of 100-200 degrees. It should also be clear less power is being produced in that situation.