How much smoke is optimal for fuel economy?

Right now what I'm wondering is how much smoke is optimal for fuel economy?
It should be obvious that cr
eating boost pressure uses energy, both with back pressure from the turbo and more resistant in the compression stroke. Thus, if you're creating unnecessary boost you're wasting diesel.

What's the optimal level of fuel to air? I've read anywhere from stoich (14.7:1) to around 17-18:1 which is the "smoke limit" where smoke generally makes itself seen.

Has anyone done dyno tests?

No matter how much I try I can't make any smoke (even at night with a car behind me I can't make out any haze) which leads me to think that I am running far too lean.

Good, it sounds like you're engine is running pretty efficiently and not just dumping fuel in.

Sbeghan said:

Right now what I'm wondering is how much smoke is optimal for fuel economy?
It should be obvious that cr
eating boost pressure uses energy, both with back pressure from the turbo and more resistant in the compression stroke. Thus, if you're creating unnecessary boost you're wasting diesel.

What's the optimal level of fuel to air? I've read anywhere from stoich (14.7:1) to around 17-18:1 which is the "smoke limit" where smoke generally makes itself seen.

Has anyone done dyno tests?

No matter how much I try I can't make any smoke (even at night with a car behind me I can't make out any haze) which leads me to think that I am running far too lean.

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Troll much? The TDI only requests boost to match the fuel map, not the other way around. If you're smoking you're not making enough boost for the fuel you're pouring into your engine and thus not burning it completely.

Well, I'm thinking that I want to look for the lightest amount of smoke and then maybe cut back just a bit or leave it there. As while smoking is bad (wasted fuel), no smoke is wasted air, yah?
Every other TDI I've driven will smoke when I stomp on it.

No the efficiency of the burn is where it's at, if the fuel is injected just at the right time for the right length of time and burnt perfectly then you really shouldn't get smoke but better economy.

Why do you want to see smoke?

Sbeghan said:

Well, I'm thinking that I want to look for the lightest amount of smoke and then maybe cut back just a bit or leave it there. As while smoking is bad (wasted fuel), no smoke is wasted air, yah?
Every other TDI I've driven will smoke when I stomp on it.

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A stock TDI won't smoke except briefly at a cold start unless something is wrong. The turbo only provides the amount of air the ECU asks for, nothing is wasted. If you cut the air back until it smokes you don't burn your fuel completely and that reduces your economy. If you hold the air constant and add fuel until it smokes, you're using more fuel reducing your economy. I don't understand why this is such a hard concept for you to grasp.

If it doesn't look like high noon in Beijing, your injector nozzles are still too small!

fnjimmy! said:

A stock TDI won't smoke except briefly at a cold start unless something is wrong. The turbo only provides the amount of air the ECU asks for, nothing is wasted. If you cut the air back until it smokes you don't burn your fuel completely and that reduces your economy. If you hold the air constant and add fuel until it smokes, you're using more fuel reducing your economy. I don't understand why this is such a hard concept for you to grasp.

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Why so mad bro??

Sent from my SPH-L710 using Tapatalk 2

Ib4tl

JarHead said:

Why so mad bro??

Sent from my SPH-L710 using Tapatalk 2

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LOL!

TDIClub, where "facts" = "mad"

I don't understand why its such a hard concept for some of you to grasp that its possible to waste air.
Yes, air is free, up to 450-500mg/stroke which is boost free atmospheric pressure. Can't waste air then. Run as lean as you want.
If I'm asking for 25mg fuel and its giving me boost its wasting fuel because its wasting air that it doesn't need (And if you ask for 25mg fuel it WILL give you boost, about 7 psi). On an ALH the smoke map says at 2000 rpm that you can inject 25mg/stroke fuel at 500mg/stroke air which you get at 1000mbar pressure. The boost target map says that at 25mg/stroke fuel you get 1500mbar pressure. That extra 500mbar of boost is not magically free.

But I don't want to get into a discussion about the ECU programming. What I want to know is, what's the optimal amount of fuel and air to get maximum work?

What is smoke? Can be unburned or partially burned fuel, particulate matter that's a side-effect of diesel combustion, or crankcase oil that's a side effect of blowby or a worn turbo. All TDIs before DPFs will emit some matter under certain driving conditions that can be seen as smoke. And all TDIs will burn fuel with varying efficiency depending on setup, condition, load, and driving habits. I can make my wagon smoke profusely by catching the turbo off boost and requesting a lot of fuel. And it will smoke after a long run at low boost because it's cleaning the accumulated particulates out of the exhaust.

Short answer to optimum efficiency is factory settings on fueling with advanced timing. Further advancing timing and increasing boost through tuning can help, but to a limited degree. And consistent boost at the RPMs where you normally drive will have a bigger impact on economy than whether or not you're over-fueled. Just ask someone with a 2260 in their car.

IndigoBlueWagon said:

What is smoke? Can be unburned or partially burned fuel, particulate matter that's a side-effect of diesel combustion, or crankcase oil that's a side effect of blowby or a worn turbo. All TDIs before DPFs will emit some matter under certain driving conditions that can be seen as smoke. And all TDIs will burn fuel with varying efficiency depending on setup, condition, load, and driving habits. I can make my wagon smoke profusely by catching the turbo off boost and requesting a lot of fuel. And it will smoke after a long run at low boost because it's cleaning the accumulated particulates out of the exhaust.

Short answer to optimum efficiency is factory settings on fueling with advanced timing. Further advancing timing and increasing boost through tuning can help, but to a limited degree. And consistent boost at the RPMs where you normally drive will have a bigger impact on economy than whether or not you're over-fueled. Just ask someone with a 2260 in their car.

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I agree with all of this. The only thing I would add is I don't consider blowing the crap out of the exhaust system "smoke" as it's not occurring in direct relation to the combustion events that are causing it to be blown out the pipe. IE it's "smoke" that already happened, collected and concentrated over time and then purged instantaneously in a visible manner.

>... what's the optimal amount of fuel and air to get maximum work?

The optimum point is a lean burn / zero smoke at zero boost (i.e., low RPMs). This isn't best for the gearbox but that's not what you were asking. Once you start using boost you are out of the optimum zone. If you see smoke then you are wasting fuel.

I was start with saying that stoichiometric ratio for gas is an AFR (by mass) of 14.7:1 (actually between 14.7 and 14.8 depending on the octane and quality of gas also assuming that it is pure gas).

Diesel stoich is 14.5:1 all that means is that it should have a complete burn with lowest emissions if injection timing is correct for the load and RPM.

A question you asked was "What I want to know is, what's the optimal amount of fuel and air to get maximum work?"

That depends on how you define "work" is work max HP/TQ or is work getting/keeping the car moving at a consistent speed using the smallest amount or resources regardless of load?

The first definition of work you really need load dyno and adjust fueling, boost, and timing across the entire achievable RPM and load range regardless of smoke.

The second definition you would want to run with the smallest amount of fuel to keep the engine running and to produce the amount of HP needed to not slow down. That could be 15.2:1 or it could be 26:1 it all depends of the efficiency of the drive train and the load placed on the engine.

To answer the title on this topic "How much smoke is optimal for fuel economy?" about 0.

Sbeghan said:

Well, I'm thinking

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No, you're not thinking. You're speculating WILDLY.

Sbeghan said:

no smoke is wasted air, yah?

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This is, hands down, the silliest logical fallacy I've ever seen.

I'm laughing so hard right now I can't even give a clear answer to your question; then again, there is no more to ad.......

The piston doesn't move because the fuel is expanding, it moves because the air is expanding. All you need to do is figure out how to get more air without requiring the same percentage increase in fuel.
Smoke is a sign that the lean, (fuel economical), expansion is using more fuel and is approaching the limit, and that just means that the trade-off of lower fuel economy for more power is very near the point of even lower fuel economy for no additional power.

I've got it, I've figured out how to get the best possible mpg's! A can of gasoline and a box of matches, that way you can have smoke and good mpg's! Go me, I'm a flippin genius and even surprise myself sometimes

Facepalm

Bill

Seatman said:

I've got it, I've figured out how to get the best possible mpg's! A can of gasoline and a box of matches, that way you can have smoke and good mpg's! Go me, I'm a flippin genius and even surprise myself sometimes

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amidoinitrite?

Now that's a definite fuel saving right there and you get free heat! + Smoke?

fnjimmy! said:

amidoinitrite?...

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I have to confess that I had to google that LOL

The great thing about a turbocharger is that it allows you to scavenge wasted heat out the exhaust, expand it through the exhaust turbine and use that scavenged energy to overcome pumping losses on the intake side. This is where the increased economy of a turbocharger comes from.

Also on the plus side, a turbocharger allows you to produce much more power from an engine vs. a normally aspirated engine of a similar size.

So: wasted air? Sure, there is some wasted energy particularly if the turbocharger is trying to produce maximum boost at low engine load. But the engine management system and proper turbocharger sizing does not allow that.

Think of it this way. If extra air is charged into the cylinder, you will use extra energy in compressing it. But air will spring back, particularly if it absorbs heat from the cylinder walls (we are ignoring the obvious effects from combustion in order to isolate the 'extra' air problem). That spring back represents energy that will be recovered on the next piston stroke.

So really, the losses from pumping extra air are not a large loss, are mainly overcome with efficiencies gained from harvesting energy from the hot exhaust by the turbocharger, and aid combustion by providing excess air where it can be most efficiently used in the cylinder.

I think you'd see better efficiency gains by: 1) replacing all the bearings in the rollers of the timing belt path with ceramic ball bearings and 2) replacing flat tappet lifters under the cam with roller lifters.

Cheers,

PH

I think what the OP is trying to do is cut down on boost, as he sees boost as wasted energy. Trying to cut boost out of highway cruise to try and increase MPG.

IndigoBlueWagon said:

Short answer to optimum efficiency is factory settings on fueling with advanced timing. Further advancing timing and increasing boost through tuning can help, but to a limited degree. And consistent boost at the RPMs where you normally drive will have a bigger impact on economy than whether or not you're over-fueled. Just ask someone with a 2260 in their car.

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Si, correcto.
There is an optimal point somewhere when it comes to boost pressure and efficiency. You convert hot expanding exhaust gases into mechanical energy through the turbo, but to a point. Too boost and you start losing efficiency because of increased pumping losses. If you ran with no boost, then you go the other way. Your volumetric efficiency is terrible and you end up running richer to make the same power -> wasted fuel.
Moderate (couple psi) increases in boost a cruising speed/load show little to no difference. Advance timing, there you go. Magic wand.
Ben

http://www.ecuconnections.com/forum/viewtopic.php?f=2&t=5058&hilit=economy

http://www.ecuconnections.com/forum/viewtopic.php?f=2&t=9612&hilit=good+old+days
From the first thread

No. Let me explain why: you need energy to make the turbo boost! You then lose energy so that the MAXIMUM amount of power produced by your engine is higher.

A 4l engine with no boost would be more powerfull than a 2l engine with 2bar turbo pressure even if injection quantities are equal.

I have built my own boost controler and at first it would oscillate all the time. At 100km/h when the boost increase of 5psi, you can feel the car slowing down a little!!!!



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