Exactly, we are not talking about more total energy (heat), we are really talking about the combustion taking place outside of the cylinders where it can cause damage. Although this results in locally higher EGT (due to the combustion), it would probably result in lower temperatures downstream, after the combustion products are mixed. It took me a while to understand his point.

So where exactly is this new supply of oxygen coming from ?

Taking the example to the extreme, if you had no oxygen, the mixture would be extremly rich but the EGT would be very low because the fuel would not burn.

So where is the "knee" in the curve?

P E H

If I understand the argument he's making, a fairly large percentage of excess O2 is required to ensure complete combustion during the time allowed by the power stroke. If there is only a small percentage of excess O2, the combustion process will be less efficient and will not be completed by the time the exhaust valves open (possibly due to imperfect mixing within the combustion chamber?). At that point the mixture, including some unburned O2 will continue to burn as it enters the exhaust manifold. It also seems (to me anyway) that there could be additional O2 available in the exhaust manifold (possibly due to intake/exhaust valve overlap?). Im also trying to understand why people would observe higher EGTs with richer mixtures.

I once had a Mercury Capri and was returning from Long Island back to Detroit. It began to lose power and finally wouldn't go faster than about 40 mph. We thought it jumped a tooth on the timing belt and the cam was late.

It stalled several times on the trip back. I recall one of these stalls. We opened the hood and the exhaust manifold was so red that it seemed translucent. Just unbelievable heat.

We fiddled with the points and got it running again. Ran like crap. Stalled once or twice again. Got to Detroit, finally, about 8 hours behind schedule.

Turned out that the rubbing block for the points had worn and the dwell angle went to nothing. Timing was very late and the fuel was burning in the exhaust. Put new points, and plugs in it and it was fine. No damage to the valves from the excessive heat.

So, I'm convinced that anything that delays combustion and allows it to continue into the exhaust manifold will raise the EGT. But, the EGT is climbing not from the addition of more fuel, or the engine doing more work, it's just caused by late or incomplete combustion in the cylinder.

I believe that was BHD's point, it just took us a while to get there.

I am not buying it on a diesel...
You have the same mixture in the combustion chamber AND the entire Power Stroke for it to burn... The CO2 , if it is going to inhibit the combustion... which I am pretty sure it will do... will be the same thing to affect it after the power stroke and on the exhaust stroke... where the expansion of the gases during the power stroke will have given the mixture plenty of cool down time...
Anyone seen what happens to the exhaust smoke when the fuel is injected late ? And in that situation you DO still have that ' extra ' oxygen in there and no CO2 for inhibition purposes....
In gasoline engines the fuel is part of the cooling process.. that is why too little fuel will overheat the engine... and the ignition is caused by a spark plug.. very different from the short period at which the air is compressed and hot enough for complete combustion in the diesel cycle...

This is how a gasser works...its opposite in a diesel.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Stick an EGT pyrometer on a gasser and richen up the mixture...EGT drops..

do the same on a diesel and the EGT climbs......

I have EGT guages on two of my three diesels and the IP has been turned up in those two....this effect is far easier to see on a N/A diesel....in fact try it on a 6.2 GM diesel....it can be turned up without removing the IP to do it...

The normal excess of air in a diesel is far less so on a Non turbo...however that excess can quickly become insufficient when you do something that will reduce the percentage of O2 in the intake air charge. And the end result is the very same if you increase th efuel delivery without making coresponding changes to the intake air charge to maintain that the O2 availible excedes the needs for complete combustion. Too much fuel for too little air makes for high EGT....doesn't matter if you deprive it of O2 via CO2 indroduction or it you crank up the fuel delivery without making changes to the intake air volume. End result is the same.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

you have injected co2 into your diesels?

or is this theory?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

CO2 does not combust....it dispaces O2 that does....basic chemistry...

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

"combustion. Too much fuel for too little air makes for high EGT....doesn't matter if you deprive it of O2 via CO2 indroduction or it you crank up the fuel delivery without making changes to the intake air volume. End result is the same."-TGHD

To help you get a grip on why this is not true.... lets take the extreme example on the spectrum.... you send into the intake increasing amounts of Nitrogen compared to Oxygen.... and you are claiming that the EGT will continue to rise if the fuel input is increased at the same time...

But at some point you should be able to visualize the END OF COMBUSTION... and thus the end of the heat producing conditions inside the combustion chamber...

Now, back off that extreme... and you will find a place where the decrease in the available oxygen starts starving the combustion process and thus subtracts heat from the situation regardless of the amount of fuel added.
That is the condition I think exists when you add CO2 into the air stream, depriving the combustion process of oxygen.

In other words, you take the normal 79 percent Nitrogen, a non burning gas, add CO2 ...another non burning gas used in fire extinguishers and you do not have an excess of oxygen available in the overall situation to allow a continued climb in EGT just based on increase fuel input.

Anything you do to decrease O2 in the intake charge on a diesel will increase the EGT....

I used the NON turbo diesel as an easier reference to understand becasue a N/A diesel struggles to get enough air .....

Disbelieve me? Turn up your full load limit and see what happens to your egt...that will have you end up with more fuel than your have availible O2 to burn completely...your EGT will soar above 1,200 degrees and you WILL damage the engine.

Like I said...its all about how much O2 is availible for any given ammount of fuel. Total quantities do not matter...its the ratio that does...You can melt down a non-turbo OM617 on far less fuel than a factory Turbo OM617 runs happily on for 500K miles or more.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Like most blanket statements that won't hold water.... if you send only non combustion supporting gasses into the engine there won't be any combustion and you can't get any rise in the EGT ... in fact you will be cooling the air from ambient from the same process used in Air Conditioning... atomizing fuel into the combustion chamber.



Simply turning up the full load limit WITH THE SAME AMOUNT OF OXYGEN IN THE EQUATION is not comparing the effects of a REDUCTION in total oxygen available in the gas input of the equation. ( apples to oranges )



Total quantities DO matter because the capacity of the combustion chamber is limited... once you substitute a NON burning gas like CO2 then you have automatically reduced the oxygen going into the chamber... and once you do that then at some point you take away your ability to BURN more fuel... so adding the fuel once you have reached that point WILL NOT INCREASE EGT.

No...becasue you are creating a condition that does not support full adn complete combustion of the fuel injected into the engine...that is still a overly rich condition...

The analogy of cranking up the fuel is in effect the very same thing...why? Becasue we are talking a given amount or O2 in relation ot a given amount of fuel to be burned...reduce your O2 you in effect richen the mixture and raise the EGT of a diesel.

Total quantites? thats why I compared a Turbo vs non-turbo OM617.

Put the fuel quantities of the turbo through the non-turbo you get meltdown? Why becasue there is insufficient O2 availible for the volume of fuel.

Non computer controled engines are tuned based upon the given fact that O2 is a certain percentage of the air....Nitrogen and CO2 are both non-combustible gasses....Injecting CO2 artificially tampers with that ratio in effect richening it up by way of reducing availible O2.

The definition of rich being a ratio of Fuel to air where fuel excedes the optimum ratio for a full burn...

A lean ratio is where air is in excess of whats needed for full combustion...

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche