I'm aware that adding more air to a diesel engine lowers EGT's.

But I see guys on YouTube with their performance trucks rolling some serious coal when spooling up turbos. Can a person assume their EGTs are extremely high with all the unburned fuel or are EGTs more affected by timing and there is not a direct correlation between rolling coal and higher EGTs?

 

All that black smoke is a byproduct of heavy fueling and not enough air...yes that means HEAT....if it doesn't clear up once the turbo or turbos spool up then there will be a heat problem.

 

Absolutely understand where black smoke comes from. But if the fuel is unburned, then wouldn't there be less heat? This is what puzzles me.

 

As a bit of an educated guess, I would assume that the temperatures would remain around the same as if the truck was receiving the maximum amount of fuel it's capable of burning, without smoking - if that makes any sense.

In other words, I would imagine that there is a threshold where the fuel would make no difference, and would just be passed through the engine and out the exhaust as black smoke.

Given an amount of air, the truck should only be able to burn a proportionate amount of fuel. Any additional fuel that can't be burnt would end up as waste, thus generating no additional heat.

 

Heavily overfueled will lower egts as the fuel absorbs heat as it's injected into the cylinder.

This is precisely why sled pullers look for a thick but high velocity stream from their stacks....keeps egts down. There is however a crisp balance between a proper plume vs stupid.

 

So it sounds like there's a middle point for high EGTs between running excessively rich and "overly lean" (which I know in Diesel engines doesn't really exist)

 

In a fuel only application, there isint a "Too Lean" of a condition....introduce a "Oxidizer" and you can most certainly have a "Lean" condition that can be detrimental to engine components.

 

Ya...I was referring to cranking in more air via turbo/supercharging, driving up the air:fuel ratio, not adding other oxidizers like nitrous - just working with the basics, then add to that how timing would come into play...

 

What Les said in post 5 is correct...

Also what Lary said is also correct...

Seems like a paradox as both can't be correct, no?

In Lary's example the best way to demonstrate is to think about how the old "smoke switch" trick works. That leads to heavy fueling with little air and high egts. Or when someone with that big slow spooling turbo gets on it and the egts skyrocket until the turbo catches up.

Les nailed it when he pointed out the velocity of the air/exhaust.

I don't want to go down the rabbit hole here, but there is also the whole theory about how the heavy fueled and dirty 12v's survive where common rails that are clean melt down.

 

Timing plays a role in all this too.

I think that Marco from Smarty fame has done more work in this area than anyone.

Timing affects: "more vs less" power
"more vs less" smoke
"more vs less" cylinder pressure
"more vs less" smog (nox)

Too much timing can lead to detonation just like in gassers

Too little leads to lost power and unburned fuel

And then one has to be mindful of the curve throughout the rpm range and powerband. And this curve is a tricky three dimensional thing.

But that's why folks like me pay folks like Les to figure it all out.