Cooling EGT with fuel ?

Leiffi

Leiffi

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On another thread some people claimed they are getting lower EGT by adding more fuel. What's the theory behind that ? Is it really cooling or just fooling EGT probe ?
 
I've spent a ton of time on the dyno with exposed junction fast egt probes and excess fuel cools combustion. You see it even when you are spooling turbos, too much fuel cools the exhaust and kills turbine performance.
 
Pretty much every combustion process on earth will cool relative to peak if the stoichiometric ratio is too rich.
 
Joesixpack said:
I've spent a ton of time on the dyno with exposed junction fast egt probes and excess fuel cools combustion. You see it even when you are spooling turbos, too much fuel cools the exhaust and kills turbine performance.
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Yes but how ?

Raw fuel just vaporizing and cooling end gases or raw fuel cooling cylinder temps and ending combustion sooner and causing even less fuel being burned ? My bet is latter because too much fuel also makes less power.
 
When you reach a rich condition you have more fuel then the air will burn and then it becomes a cooling agent like water injection. The unburnt fuel would quench the flame in the cylinder a bit and what isn't burnt in combustion would then in turn help absorb the heat as it exits the cylinder as a fuel steam. Just my theory
 
There are a lot of papers written on this subject, both SAE and DieselNet. Though there are a lot of contributing factors, the net effect is that the burn happens faster. Ignition delay(the time between when the fuel is injected and when the burn starts) is reduced, and the speed of the combustion itself is increased. You of course can go too "rich" and engine torque will be reduced. Most people consider running stoichiometric mixtures will produce maximum hp, but this is rarely the case. Mixtures slightly richer the stoichiometric will generally produce more hp, with lower EGT's, though some exhaust emissions will be higher.

If you have access to DieselNet articles this is a great one to read: https://www.dieselnet.com/tech/diesel_comb.php

Paul
 
paulb said:
Ignition delay(the time between when the fuel is injected and when the burn starts) is reduced, and the speed of the combustion itself is increased.

Paul
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How can ignition delay be reduced when that extra fuel is added to the end of injection period ?
 
DISTURBED said:
When you reach a rich condition you have more fuel then the air will burn and then it becomes a cooling agent like water injection. The unburnt fuel would quench the flame in the cylinder a bit and what isn't burnt in combustion would then in turn help absorb the heat as it exits the cylinder as a fuel steam. Just my theory
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Like I asked earlier, why not just reduce fuel to get lower EGT. Added bonus is no cylinder wall washing and no risk for flame out.
 
Leiffi said:
Like I asked earlier, why not just reduce fuel to get lower EGT. Added bonus is no cylinder wall washing and no risk for flame out.
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If your talking about a sled pulling motor that just doesn't work.
 
Leiffi said:
Like I asked earlier, why not just reduce fuel to get lower EGT. Added bonus is no cylinder wall washing and no risk for flame out.
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reducing fuel will increase EGT if you're already using it to lower EGT

otherwise it just reduces power

how much cylinder washing do you think is occurring in a direct injected diesel with the fuel being injected into the piston bowl? :confused:
 
I noted with a data logger as well, excess fuel cools egt.
 
Scooter's Roofing said:
reducing fuel will increase EGT if you're already using it to lower EGT

otherwise it just reduces power

how much cylinder washing do you think is occurring in a direct injected diesel with the fuel being injected into the piston bowl? :confused:
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Forget EGT, power is most important.

A lot. Because raw fuel is still there when gases are pushed out of the cylinders.
 
I think the term "raw fuel" is being used a little lightly.

Power is important. Keeping the engine together is most important.
 
Leiffi said:
Yes but how ?

Raw fuel just vaporizing and cooling end gases or raw fuel cooling cylinder temps and ending combustion sooner and causing even less fuel being burned ? My bet is latter because too much fuel also makes less power.
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Likely both, fuel impingement on combustion surfaces pulls heat from that surface as well as excess vaporizing in a low to no oxygen condition.


Leiffi said:
Forget EGT, power is most important.

A lot. Because raw fuel is still there when gases are pushed out of the cylinders.
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Max power is SMOKEY. Get over it.

YES excess fuel will start to pull power but its not when you start to see a little bit of smoke. Look at my avatar, that is still max power on the dyno but pulled over 200 degrees of egt's.

There used to be common rail's melting down left and right sled pulling burning completely clean simply from exceeding the maximum heat rejection capacity of the cylinders.
 
When you're not permitted to run water injection, you have 2 options.

Cut fuel back to where it does not melt pistons and get your azz waxed because you make 400hp less than everyone else,

Add fuel till you quench the fire enough to keep from melting pistons and make some power.
 
Leiffi said:
many pullers has found out that less fuel makes more power. Forget EGT, its just a number.
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And they probably can't make it through a season without melting a piston.....
I'm happy around 1700-1800 degrees.

Like joesixpack said max HP is smokey. Then add more fuel to cool egts with a very small amount of HP loss if any.
 
I love discussions like this..Someone tell me if I'm wrong here...

In my mind, adding fuel beyond the point of max power means more hydrogen will combine with oxygen to create steam, and the additional carbon will pass through to make for big plumes of smokey goodness. So essentially, we trade away some thermal energy for an increased mole count. The net result is a similar expansive effort and the same amount of work acting on the piston.

Yes, no? Full retard?
 
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