LOP Questions

[jlunseth]

Some wrong statements here. LOP results in lower cylinder temps, having nothing to do with lower power. I run consistently LOP at 71% with significantly cooler CHTs than an equivalent ROP setting. The reason for cooler temps is not extra air cooling the cylinders, it is changing the power curve produced by the combustion process, to slow it down so the result is more of a push than a blow. It is the high Internal Cylinder Pressure resulting from more rapid combustion that raises temps. One could achieve the same result (slowing the combustion curve) with a ROP setting, but the fuel flow would be much higher than what is in the POH and higher than we are conditioned to think of as normal, so nobody does it that way. For 231 operators, the fuel flow to do that would be somewhere in the 14-15 GPH range where the POH uses numbers in the twelves. Even 125 degrees ROP is about 13.5 at 75%.

The percent HP function in the JPI, at least the one I have, is not accurate in either ROP or LOP. I just ignore it. When I operate ROP it is off by at least 8 percentage points. When LOP, if I have not put the unit in LOP lean find mode, it is ridiculously off because it is using the ROP power algorithm, which is completely different from the LOP algorithm. If I do use the LOP lean find mode, the percent power will be more accurate because it uses the LOP power formula, but the degrees lean of peak readings (the hanging icicles) will be wrong.

When using the “big pull” method, you should not use the LOP lean function, in fact, from what I can tell in my engine you should never use the LOP lean function at all, not in a 231, because it does not result in a measure of degrees lean of peak that has any accuracy. You do the big pull first, and then if you want to find a setting that is x degrees lean of peak, you use the “first cylinder to peak” leaning function in the JPI, also known as the ROP lean function, and you read that right, the ROP lean function. You enrich the mixture until the first cylinder peaks, then go back lean of peak the desired number of degrees. The JPI does not have a clue when you use one of the lean functions, if you are lean or rich of peak. It only measures first cylinder to peak (ROP lean function) or last cylinder to peak (LOP lean function). If you do the big pull followed by the ROP lean function, the change in the mixture is relatively small and you will get a reasonably accurate measure. Yes, I know, your EGT graphs won’t hang upside down and the percent power number will be way off. It is the engine you are concerned with, not the picture on your JPI screen. 

As I have said before, the JPI lean function is designed using assumptions, not measurements. The assumptions don’t work in an engine with power controls like the 231. Think of an NA engine. You leave the throttle wide open and then you lean the fuel out to go LOP. The MP does not change at all unless you change altitude. The JPI assumes that you are changing only fuel flow as you lean out, and not MP. That is one of the design assumptions in the JPI lean function. In the 231 the MP changes when you change the fuel flow. When you change both at the same time, you do not find a valid peak, not one you can use to make a setting where you have changed both MP and fuel flow some more. In fact, if the interlink worked perfectly you would not be lean of peak at all, you would be at the very same rich of peak air/fuel ratio you started with, just at a lower power setting. The interlink does not appear to me to work perfectly when fuel flow is changed, but it is trying, it changes MP. MP also changes simply because power output is dropping, and therefore the turbo is slowing down.

Also remember that LOP operation is, by definition, a lean fuel/air ratio - more air than is needed for the available fuel. One way to get that is by reducing the fuel flow while leaving the MP the same. There is another way, and that is by increasing the MP while leaving the fuel flow the same. Increasing the MP has no effect on the power produced when LOP, the power is entirely dependent on fuel flow, at least that is what the GAMI guys teach us. So you can find a lean of peak setting at, say, 30”, and if you want to go more lean of peak without changing the power output, you can increase the MP to 32 or 34, as long as you keep adjusting the fuel flow so it stays at the same number and as long as your engine stays smooth. I find that if I do that in my engine, there is a little bit of a power increase, but not nearly as much as you would find if the settings were ROP settings, where power is much more dependent on MP.

If you have a valid power setting and either MP or fuel flow changes, just do what Paul says, put it back, but remember to make sure both values go back where they were.

[exM20K]

10 hours ago, jlunseth said:

Increasing the MP has no effect on the power produced when LOP, the power is entirely dependent on fuel flow, at least that is what the GAMI guys teach us.

Fuel flow on the CMI system does vary with MAP.  Do you lean when you reduce power in the descent? 

Good essay on leaning and LOP from the Dean of LOP here.

[jlunseth]

52 minutes ago, exM20K said:

Fuel flow on the CMI system does vary with MAP.  Do you lean when you reduce power in the descent? 

In practice, I set my cruise power setting which is 34” and 11.1 GPH. That is about 71% power. It works in my engine up to about 15 or 16k where I can’t keep the TIT at or under 1600 any longer, so I will go ROP. For the descent, I just pull off an inch or so of MP and tip the nose over, assuming clear air, and enjoy the ride. The MP has to be adjusted as the plane descends to stay at or under 34”. I use the same 34” at 3,000 MSL that I do at 10k. If I want to slow to an approach speed I just pull the MP back to 24-25”, whatever gives me 120 KIAS, depends on the OAT. The fuel flow comes back with the MP so at 24 it is about 8.2 GPH and at 25 it is around 8.6. If I want to slow from cruise but not go all the way to 25” I just pull the MP back, the FF comes with it, and generally the lower MP mixes are leaner than my 34” and 11.1. I keep the fuel leaned out even during the final approach so I don’t get burbling in the engine, but either somewhere over the fence, or on the ground, I put some full flow in just so I don’t have to push the knob so far to full if I have to go around.  This works in my engine, which has GAMI’s. The 8.6 GPH setting at 25” is somewhat lower than Paul’s (gsxpilot) 25 and 9.5. Mine results in about 56% power. I use that for maneuvering, approaches, holds and the like. I have not done a lean find in a few years. I just use settings that I know work, and with the cruise setting I manage to a max TIT of 1600. If the TIT goes over that I pull off a little fuel to cool it, but somewhere around 10.7-10.8 I just switch to ROP. EGTs will be about 100 dF higher than an equivalent ROP setting, and CHTs will be cooler. I have just one cylinder that runs warmer than the rest likely because the baffling is not doing a great job. My compression tests, on an engine with nearly 2100 hours, have been slowly improving in the last three years, except for the warm cylinder which is about level or falling a little.

[A64Pilot]

You get more power if you add more air even LOP because our engines develop power by the rapid expansion of air when it’s heated, if you have more air mass to heat you will get more power. Of course there is a limit as to how lean you can be and still get combustion, that’s the difference between us and Diesels. It’s not a whole lot of power and often it’s masked by the power loss of being too lean and uneven combustion.

‘Internal combustion engines do not get power from “exploding fuel” there should be no explosions, just burns, explosions are detonation and we know what that does.

To get an idea how spark ignition engines operate LOP, it helps to have an in-depth understanding of the Diesel engine principles, Diesels only throttle fuel, there is no air throttle, they are the ultimate LOP engine if you will, even turbines throttle air through inlet guide vanes, bleed valves etc. There is never any vacuum in the intake manifold of a Diesel, if you put a manifold pressure gauge on an NA Diesel regardless of throttle setting and RPM/ load, at sea level it should always read about 30”, even at idle.

A turbo Diesel will have a max pressure limit often controlled by a waste gate, but other than that the engines gets all the air it can even at idle.

Edited May 21, 2021 by A64Pilot

[carusoam]

The challenge of adding more air...

There is only so much heat to expand all of the air...

Net result... you are compressing as much air as it expands... it adds a bit of frictional losses with that... but no additional power...

+1 for the extra air not really cooling the flame temperature inside the cylinder.... but the extra molecules get in the way of gas and oxygen meeting.... so the reaction time is slowing down...   

The flame temperature is set by the chemicals involved....
 

Does anyone fly their plane LOP in the climb?

It was something I contemplated early on... but the reality of it.... the climb isn’t that long where I’m going... and the risk of goofing something up is much larger...

PP thoughts only, not a chemist...

Best regards,

-a-

[jlunseth]

5 hours ago, carusoam said:

Does anyone fly their plane LOP in the climb?

It was something I contemplated early on... but the reality of it.... the climb isn’t that long where I’m going... and the risk of goofing something up is much larger...

 

On occasion, if I have a short climb, I will just leave my LOP cruise power setting where it is and climb the aircraft. I am talking about the situation where, say, you are departing a Bravo and the controller has you under your filed altitude by a couple of thousand feet for quite awhile, so you put the cruise setting in, and then the controller gives you your filed altitude and you have one or two thousand to climb. But it does not work well for a long climb in my aircraft, esp. a climb to the high teens/flight levels, there is too much heat build up. There can be quite a bit of heat build up on a hot summer day, long climb, even if you are full power full rich. Maybe it would work in an NA, don't know. If the temps build up you can just push the knobs in, mixture and prop for us 231 guys. 

[N201MKTurbo]

6 hours ago, carusoam said:

Does anyone fly their plane LOP in the climb?

I have to agree with @jlunseth. I will do a cruise climb LOP. The problem is, I cruise at MAX LOP power. Either limited by CHTs or TIT. There is no way to increase power without exceeding your temps. The reduced airspeed further exasperates the problem. The only way to get climb power is ROP.

[Bob - S50]

Me too, me too.  If I've already leaned and then I want to climb only 1000' or 2000' and I'm not in a hurry, I'll leave the mixture set.  If I'm climbing 1000' I'll increase the MP by 1" and set a slow rate of climb like 200 or 300 FPM.  I just make sure the climb rate doesn't slow me down so much that I drastically reducing cooling air over the engine.  By increasing the MP 1" for each 1000' of climb, once I level off, I'll have the same power setting I had when the climb started and I won't need to lean again.

[A64Pilot]

You can run LOP at any altitude and any flight condition without harm, so long as you don’t increase power by too much, if you do you could cause harm. I didn’t say you will cause harm, just saying that at high power it’s possible to if lean.

For me the fuel saving isn’t worth the risk. Let’s say you have a 10 min climb, and your burning 10 GPH more being ROP. I’m a simpleton and like simple numbers.

‘So that climb is 1/6 of an hour, so you will save 1.6 gallons LOP, and that’s with a 10 GPH difference, which is probably a little excessive. Check my math, I’m not good at math

But if I’m turning and need to climb 1000 ft to maintain correct altitude, then I’ll leave power alone and just slow to climb.

‘But in cruise flight when traveling I’m often up high for comfort and am leaned out and at full throttle due to HP loss at altitude, so then I’ll just slow at little to climb as going rich isn’t a whole lot more power anyway.

‘You could of course climb ROP to say 7500 then transition to LOP and continue the climb, but I don’t but then my cruise is usually around 9 to 10 thousand anyway.

[Shadrach]

On 5/20/2021 at 10:27 AM, A64Pilot said:

what you would want is an O2 sensor, that will tell you mixture ratio accurately based on remaining oxygen, of course it’s how computer controlled automobiles precisely trim fuel. I know someone with a Maule that has one, put it in as a field approval, it is a monitor only of course, it does not control anything

But here’s the thing, leaded fuel is supposed to kill a lambda sensor in a hurry, but last I heard it hasn’t yet. When it does they are relatively cheap and as easy to change as a spark plug

There is a whole lot of misinformation “sold” about LOP, like “excess” air cools your cylinder heads etc. So tell me how does exhaust thats 25 degrees cooler than peak cool anything?

Cylinder head temp is function of power, it’s the lower power that makes the heads cooler.

Flame suit on.

On edit, airflow sensors are easy the more modern ones are just a heated wire, air mass is measured by how which the wire is cooled, the older ones were a door, but it’s air mass you really are measuring, and that’s of course what you want to measure, by measuring mass, it autocorrects for density altitude. 

Your understanding of combustion science seems very basic. It’s clear that you believe your misunderstanding to be misinformation. 
What’s also clear that you’ve never taken the time to look at or understand a BSFC graph. BSFC simply stated is the amount of fuel used to make a unit of power. The lower the BSFC, the less fuel required to make a unit of power. The lowest BSFC numbers for any aero engine currently in service occur on the lean side of peak EGT...This is not opinion, it is not sales, it is not misinformation...it is combustion science and has been well understood for nearly 80 years. 

A bit about “Air Cooling Cylinder Heads”...  From a combustion standpoint, surplus air does not cool the cylinder and neither does surplus fuel, but folks like to state things simply. If I were to tell a new pilot to enrichen the mixture to keep CHTs cool in a climb that would make sense to him. If I tell a new pilot to enrichen the mixture in order to slow the combustion event in order to reduce peak internal cylinder pressure in order to reduce CHTs he’s going to look at me cross eyed.  Brevity in the cockpit is a good thing. It doesn’t explain the why, only cause and effect. Surplus air (LOP) or surplus fuel (ROP) can be used to control the speed of the combustion event relative to piston/crank position. By adding more fuel or more air the flame front’s progress is inhibited by non combustible fuel molecules that have not paired with oxygen molecules (ROP) or by non-combustible Oxygen molecules that have not paired with a fuel molecule (LOP).  A surplus of either one slows the combustion event and moves the peak pressure point away from TDC reducing peak pressure. Lower peak pressure means lower CHT.  Does lower peak pressure mean less power? With regard to normally aspirated engines, it typically does, by how much depends on the setting.

Cylinder head temperature is not a function of power. It is a function of internal cylinder pressure and is greatly influenced by peak cylinder pressure.

Power is a function of the Mean Effective Pressure.

The same Mean Effective Pressure can be produced at a number of mixture settings. ROP settings tend produce higher peak pressure early in the power stroke. LOP mixture settings tend to produce lower peak pressure but more even pressure throughout the power stroke. 

Indeed there is power loss in a normal aspirated engine going from ROP to LOP. However the corresponding reduction in CHT is not simply due to that power reduction. There are many other factors at play. Folks with turbo engines don’t have to take the power loss, they can add additional manifold pressure and run at the same horsepower level as long as they’re not limited by TIT or MP restrictions. Two turbo engines can be set for 75% power and yield the same speed while burning dramatically different amounts of fuel and generating very different CHT numbers. This is not “Sales”, this is not “misinformation”, this is well understood science.

Your posts bother me not because you’re ignorant (we’re all guilty of that) but because you seem to know so much that isn’t so...

 

Edited June 7, 2021 by Shadrach

[A64Pilot]

I am not the one who printed an article trying to sell injectors and claimed that excess air cooled cylinder heads when LOP, your “combustion scientist” did. 

He made thet statement over and over, it was one of his prime selling points. That’s been years ago, one I read when I bought Gami injectors for both the C-210 and Maule, maybe 04 or so?

But what has come out over and over with your posts abdicating use of non approved parts etc is your belief that your more knowledge than the FAA etc.

‘In the Army you woud have been an outhouse lawyer

[Shadrach]

25 minutes ago, A64Pilot said:

I am not the one who printed an article trying to sell injectors and claimed that excess air cooled cylinder heads when LOP, your “combustion scientist” did. 

He made thet statement over and over, it was one of his prime selling points. That’s been years ago, one I read when I bought Gami injectors for both the C-210 and Maule, maybe 04 or so?

But what has come out over and over with your posts abdicating use of non approved parts etc is your belief that your more knowledge than the FAA etc.

‘In the Army you woud have been an outhouse lawyer

Show me he quotes (in context please) 

George Braly, John Deakin and Walt Atkinson have done more to educate operators with the facts surrounding applied combustion science than any other individual, group or organization in the last five decades.  Regardless of the users preferred mixture setting there are gains to be had in efficiency, smoothness and in available efficiency ratios by normalizing F/A ratios from cylinder to cylinder...AKA GAMI spread. Many people are driven to buy GAMI injectors because they’re trying to access efficiency ratios (mixture settings) that their factory engine will not achieve smoothly. That does not mean there are no other benefits.  BTW - This is coming from someone who has never purchased Gami injectors nor taken an APS course.  Nevertheless, I am truly grateful to those gentleman for what they’ve freely given to the community. I’m not ashamed to say that it pisses me off when someone suggests that they peddle misinformation to sell injectors. It’s an ignorant statement and someone with your experience should know better. In the case of a conforming engine, GAMI would be the first to tell you that you don’t need their product. Most injected angle valve Lycomings do not need GAMI injectors although I’ve recently heard anecdotal reports of Lycoming delivering engines with pretty lousy fuel distribution.

[Ragsf15e]

1 hour ago, A64Pilot said:

I am not the one who printed an article trying to sell injectors and claimed that excess air cooled cylinder heads when LOP, your “combustion scientist” did. 

He made thet statement over and over, it was one of his prime selling points. That’s been years ago, one I read when I bought Gami injectors for both the C-210 and Maule, maybe 04 or so?

But what has come out over and over with your posts abdicating use of non approved parts etc is your belief that your more knowledge than the FAA etc.

‘In the Army you woud have been an outhouse lawyer

Luckily we’re not in the army (anymore).

[jlunseth]

Don’t want to argue. I am sure some people have made the simplistic statement that excess air or excess fuel cools cylinders by absorbing and carrying off excess temp. To a very small degree, inconsequential to the health of the engine, that is probably true. But the point Shadrach makes that slowing the combustion event and reducing ICP is what actually cools the CHT’s, is proven science. Those of us lucky enough to attend the APS/GAMI live class in Ada saw that for ourselves, with an engine being actually run on a test bed.

I took some pictures of my cruise setting on my last Angel Flight, so people could see for themselves what the result looks like. My setting is 34” of MP, in this instance 11.4 GPH, and 2450 RPM. Normally, I would tweak the fuel flow down to 11.0-.1 GPH but the cooling conditions were really good and I didn’t bother. Also, my number 2 cylinder, as I have said before, runs warm. There is a warp in the baffle behind it, it is the cylinder closest to the firewall. My LOP operated engine is now about 280 hours over TBO so not much point in fussing with the baffling with a possible overhaul in the future. On the other hand, with the compressions in each cylinder either stable or improving there is not much incentive to re-engine either.

Please note the CHTs at 71% HP with the cowl flaps fully closed. Also, ignore the percent HP display, the JPI is calculating that number assuming the engine is ROP and it is not. As I have said before, the LOP lean find on the JPI, which would give the correct %HP number, is not worth the effort.

Aaagh, Anthony, can you work your magic. I am on an iPad and don’t have the tools to flip the photos.

[squeaky.stow]

4 hours ago, Shadrach said:

GAMI would be the first to tell you that you don’t need their product.

True. I sent my monitor data to GAMI when I first bought my 252 and asked them if I could order a set of GAMI injectors. They told me my spread was .3 and I would be wasting my money trying to improve it. That convinced me of their integrity.

2 hours ago, jlunseth said:

I took some pictures of my cruise setting on my last Angel Flight

Not to derail the thread with something totally off topic but what’s with the difference between the angle of bank on the main AI and the GI275?

[jlunseth]

48 minutes ago, squeaky.stow said:

True. I sent my monitor data to GAMI when I first bought my 252 and asked them if I could order a set of GAMI injectors. They told me my spread was .3 and I would be wasting my money trying to improve it. That convinced me of their integrity.

Not to derail the thread with something totally off topic but what’s with the difference between the angle of bank on the main AI and the GI275?

New installation. My avionics shop has been advised and they are slotting the aircraft in to fix it. The 275 is correct, there was no bank.

[Shadrach]

On 5/22/2021 at 2:30 AM, carusoam said:

The challenge of adding more air...

There is only so much heat to expand all of the air...

Net result... you are compressing as much air as it expands... it adds a bit of frictional losses with that... but no additional power...

+1 for the extra air not really cooling the flame temperature inside the cylinder.... but the extra molecules get in the way of gas and oxygen meeting.... so the reaction time is slowing down...   

The flame temperature is set by the chemicals involved....
 

Does anyone fly their plane LOP in the climb?

It was something I contemplated early on... but the reality of it.... the climb isn’t that long where I’m going... and the risk of goofing something up is much larger...

PP thoughts only, not a chemist...

Best regards,

-a-

I have made small changes (2000”) while remaining LOP but I prefer to minimize the time spent in climb so it’s not my SOP. I have experimented with climbing LOP just after departure to cruise. My recollection was that the degradation in climb performance negated the fuel savings. 

Edited June 6, 2021 by Shadrach

[PT20J]

Let's think for a moment about how our engines work both LOP and ROP.

Gasoline takes time to combust and the reaction is complicated by the fact that the piston is moving and thus changing temperature and pressure during the event. Once the spark ignites it, the fire starts slowly, builds to a maximum rate and then slows down and eventually snuffs out. If the spark occurs too late, the pressure doesn't build sufficiently until the piston is already well down the cylinder and not a lot of work is done. If the spark is too early, too much pressure rise occurs while the piston is travelling up on the compression stroke and this is obviously counter productive. Intuitively, we can see that there must be an optimum timing and it it called Maximum Brake Torque (MBT) timing. It turns out that at MBT timing, half the peak pressure rise occurs by TDC and this is also the point of maximum rate of change in the pressure and the peak is generally around 16 deg ATDC. The position of the peak really doesn't matter much -- it just a byproduct of the timing. It's not the peak pressure that does the work but the average pressure. The peak magnitude is important because too much can overstress engine components (this is taken care of during design) and too much pressure causes too much compression heating and can lead to detonation. 

For reasons related to the chemistry of combustion (primarily dissociation and chemical equilibrium effects) the maximum combustion temperature occurs around 10% rich of stoichiometric and the maximum power occurs about 20% rich of stoichiometric.  An aircraft engine would normally have timing set for MBT at cruise power with the best power mixture. Any other mixture would cause the flame speed to slow and delay the peak. 

RPM has a timing effect also. Faster speed retards the pressure peak but not as much as you might think because higher rpm increases turbulence in the cylinder which increases the burn rate somewhat. Over the small range of available cruise rpm, there isn't likely a lot of effect.

When you run LOP, the burn rate decreases and this results in the pressure curve having a lower and delayed peak. This is really just showing the power loss from the timing no longer being optimum. If you could advance the timing you could get back to MBT and the peak would be back where it should be. The available power would still be less LOP than ROP because all the air is not being utilized. But, as long as you can get the power you want, LOP is more efficient.

Skip

[N201MKTurbo]

1 hour ago, PT20J said:

Let's think for a moment about how our engines work both LOP and ROP.

Gasoline takes time to combust and the reaction is complicated by the fact that the piston is moving and thus changing temperature and pressure during the event. Once the spark ignites it, the fire starts slowly, builds to a maximum rate and then slows down and eventually snuffs out. If the spark occurs too late, the pressure doesn't build sufficiently until the piston is already well down the cylinder and not a lot of work is done. If the spark is too early, too much pressure rise occurs while the piston is travelling up on the compression stroke and this is obviously counter productive. Intuitively, we can see that there must be an optimum timing and it it called Maximum Brake Torque (MBT) timing. It turns out that at MBT timing, half the peak pressure rise occurs by TDC and this is also the point of maximum rate of change in the pressure and the peak is generally around 16 deg ATDC. The position of the peak really doesn't matter much -- it just a byproduct of the timing. It's not the peak pressure that does the work but the average pressure. The peak magnitude is important because too much can overstress engine components (this is taken care of during design) and too much pressure causes too much compression heating and can lead to detonation. 

For reasons related to the chemistry of combustion (primarily dissociation and chemical equilibrium effects) the maximum combustion temperature occurs around 10% rich of stoichiometric and the maximum power occurs about 20% rich of stoichiometric.  An aircraft engine would normally have timing set for MBT at cruise power with the best power mixture. Any other mixture would cause the flame speed to slow and delay the peak. 

RPM has a timing effect also. Faster speed retards the pressure peak but not as much as you might think because higher rpm increases turbulence in the cylinder which increases the burn rate somewhat. Over the small range of available cruise rpm, there isn't likely a lot of effect.

When you run LOP, the burn rate decreases and this results in the pressure curve having a lower and delayed peak. This is really just showing the power loss from the timing no longer being optimum. If you could advance the timing you could get back to MBT and the peak would be back where it should be. The available power would still be less LOP than ROP because all the air is not being utilized. But, as long as you can get the power you want, LOP is more efficient.

Skip

I have a book published in 1938 that goes into great depth including all the calculus and chemistry, to figure out how much power an aircraft engine will produce without burning a single drop of gasoline. Anybody who thinks they didn’t understand engines back then is terribly mistaken. They even cover LOP and ROP operation.

[PT20J]

14 minutes ago, N201MKTurbo said:

I have a book published in 1938 that goes into great depth including all the calculus and chemistry, to figure out how much power an aircraft engine will produce without burning a single drop of gasoline. Anybody who thinks they didn’t understand engines back then is terribly mistaken. They even cover LOP and ROP operation.

You might find this one interesting...

NACA-TN-772.pdf

[N201MKTurbo]

1 minute ago, PT20J said:

You might find this one interesting...

NACA-TN-772.pdf 8.5 MB · 0 downloads

Thanks, looks like a good read.

Makes a good case for advancing the timing If running LOP.

[carusoam]

I enjoy the tech discussion...

And when it comes to burning fuel in a cylinder... I always make sure Ross is invited... 

He has covered what is going on in the cylinder at a level that Chemical engineers discuss in one of their favorite classes...  Physical Chemistry...

Essentially a mathematical treatment of how two chemicals react, regarding their rates of reactions.... with other non-reactive  molecules in the chamber... in this case lots of Nitrogen, CO2, and others thrown in...

When it comes to flame temps...  we probably want to include the phase changes that are occurring at the same time...

Why sending excess gasoline into the system is pretty affective at lowering the EGT... compared to excess air...

There is a very large energy absorption in the process of gasoline evaporation...

See how much energy is absorbed by evaporating a couple of extra gallons of gasoline every hour... then raising it’s temperature up to the EGT...

Heat capacities of all the reactants and products, along with all the phase changes that are included... on the way to the power stroke...

The ChEs call this doing an energy balance around the reaction....

Yes, there are combustion engineers that specialize in analyzing burning things...

+1 for the ancient engineering of chemistry... It may have preceded the combustion engine...

+1 for Having respect for all the people in the room while having a technical discussion is important... takes a bit of extra effort.  Always re-read your posts after you hit send...

It is way too easy to be accidentally insulting... (I’m still working on this myself) 

PP thoughts only, it is great to have the opportunity to discuss such a great topic, WITH everyone.

Best regards,

-a-

[carusoam]

And for my buddy JL...

Who is my favorite author of all things TC’d around here....   

Holy cow... that reminds me...   remember to include compressibility of real gasses into the energy balance... that whole PV=nRT thing...

 

This End Up!

-a-

[PT20J]

1 hour ago, carusoam said:

Why sending excess gasoline into the system is pretty affective at lowering the EGT... compared to excess air...

There is a very large energy absorption in the process of gasoline evaporation...

See how much energy is absorbed by evaporating a couple of extra gallons of gasoline every hour... then raising it’s temperature up to the EGT...

Heat capacities of all the reactants and products, along with all the phase changes that are included... on the way to the power stroke...

Anthony, Here's a source that did the math on that:

You CAN be too Rich __ Application Notes.pdf

[carusoam]

Hmmmm....

Great article Skip!

1.2 pages or so... of easy to read, right on topic... excellence...   

It even touches on the affect of pressure on the rate of combustion....

If you have a TC’d engine.... the speed of combustion can be higher... the total compression ratio really builds pressure inside the cylinder before ignition...  (turbo pressure + CR)

This is probably what gives the electronic ignition engineers the willies.... when they start discussing changing ignition timing...

Pilots want to get the most out of their combustion event...

• burn all the gasoline down to H20 and CO2 if able...
• do it within the time of 25° BTDC and when the exhaust valve starts to open...
• maximize the work done to match the best arm on the crank... as it goes from a low arm at the top of the stroke, to max arm in the middle of the stroke back to a low arm as the exhaust valve opens again...  with the best(?) pressure...
• And keep this all in mind while the volume of the chamber is changing...

Where we get the most out of this knowledge...

• How it works for us individual owners/pilots...
• What today’s goal is... Speed vs. Efficiency or something in the middle...

Flying LOP enough to have no CO early in the exhaust stream.... is a sign of getting the most energy out of the gasoline...

That would be hard to measure...

But, if we did measure a high CO content late in the exhaust stream... that would be a sign that we can do better...

That final step of converting CO to CO2... is described by (By Klaus Allmendinger, VP of Engineering, Innovate Motorsports) as two step process...

Way cool.... 

See if we can measure nmpg close enough to capture the efficiency improvements...

Now that’s complex!

This is where the instrumented engine at GAMI really earned its keep...

 

Reminder...  No prizes will be awarded for any melted piston crowns.... a side effect of pre-ignition... that can take only a minute or two...

PP thoughts only, not a combustion engineer...

Best regards,

-a-