Why IDI diesels require glow plugs

[asavage]

It's likely that your IH Six has an intake manifold heater; many did. Isuzu medium-duty trucks (think NPR) are set up that way, as are the B series Cummins I believe. Look for one or two 10 gauge wires going to a flange plate (Cummins) or a largish screw-in device (Isuzu) on the intake manifold.

[philip]

It's likely that your IH Six has an intake manifold heater; many did.

Sounds like a DT series diesel which were electronic & DI.

[Knucklehead]

Thank you Carimbo for finding that. I particularly liked the paragraph that began:

Even at equal power, a forced-air diesel engine has an advantage over a naturally aspirated engine.

[philip]

I particularly liked the paragraph that began:

Even at equal power, a forced-air diesel engine has an advantage over a naturally aspirated engine.

The whole paragraph:

"(1)Even at equal power, a forced-air diesel engine has an advantage over a naturally aspirated engine. (2)The increased air mass decreases the fuel-air ratio and, thereby improves the engine's thermal efficiency (fuel economy). (3)In addition, the decrease in fuel-air ratio at part power can also improve emissions performance, depending on other factors. "

(1)In this passage, I infer 'forced-air' to be denser than atmosphere ... because the air is pressurized unless ... there is a mitigating factor (?).
(2)So forcing air in should -increase- air/fuel ratio (ie 20:1 is a ratio increase from 10:1, right?).
(3)Decreasing (lowering) the air/fuel ratio means to me the engine is running richer ...yes? What diesel exhaust emissions benefit from this condition? NOx? Certainly soot would rise.

Help me out here Galen .

(PS: ) At times, the temperature of "Forced air" is considerably higher than atmosphere which suggests to me that without a charge cooler, one COULD have hot (much less dense) air entering the engine which would negate much of the benefit from pressurizing the air in the first place. Pressurized & hot intake air could improve fuel atomiztion (MPG) and emissions (?) Is this what Chevron means?

[moose60]

"(1)Even at equal power, a forced-air diesel engine has an advantage over a naturally aspirated engine. (2)The increased air mass decreases the fuel-air ratio and, thereby improves the engine's thermal efficiency (fuel economy). (3)In addition, the decrease in fuel-air ratio at part power can also improve emissions performance, depending on other factors. "

(1)In this passage, I infer 'forced-air' to be denser than atmosphere ... because the air is pressurized unless ... there is a mitigating factor (?).
(2)So forcing air in should -increase- air/fuel ratio (ie 20:1 is a ratio increase from 10:1, right?).
..yes? What diesel exhaust emissions benefit from this condition? NOx? Certainly soot would rise.

Philip-

The initial post states that fuel to air ratio would be decreased, where as you have (correctly) stated that air to fuel ratio would increase.
However, you kept the same ratio, ie. air to fuel, ratio when refering to the original post in #3 above.

(3)Decreasing (lowering) the air/fuel ratio means to me the engine is running richer .

You are dealing with two different ratios here.
1. Examples of air/fuel are 14/1, 20/1 etc.
2. Examples of fuel/air (as in the article) 1/15, 1/20. The article is referring to this second set of ratios. Lowering this ratio (1) leans the mixture.
Lowering 2. will enrichen the mix.
It' s just a finickey distinction.

[philip]

"(1)Even at equal power, a forced-air diesel engine has an advantage over a naturally aspirated engine. (2)The increased air mass decreases the fuel-air ratio and, thereby improves the engine's thermal efficiency (fuel economy). (3)In addition, the decrease in fuel-air ratio at part power can also improve emissions performance, depending on other factors. "

(1)In this passage, I infer 'forced-air' to be denser than atmosphere ... because the air is pressurized unless ... there is a mitigating factor (?).
(2)So forcing air in should -increase- air/fuel ratio (ie 20:1 is a ratio increase from 10:1, right?).
..yes? What diesel exhaust emissions benefit from this condition? NOx? Certainly soot would rise.

Philip-

The initial post states that fuel to air ratio would be decreased, where as you have (correctly) stated that air to fuel ratio would increase.
However, you kept the same ratio, ie. air to fuel, ratio when refering to the original post in #3 above.

There it is, by golly. You're right! In air/fuel, increasing the ratio means leaning. In fuel/air, decreasing the ratio means leaning.

In the context of diesel, I find it odd to use "fuel/air" because fuel is regulated but not air (with our vacuum controlled rack SD the exception )


Makes me wonder about the origin of the engineer or editor. Such an inversion I've seen in European tech articles.

[Knucklehead]

That reminded me of the time I watched my friend pull out a cigarette and put it in his mouth backwards.

At times, the temperature of "Forced air" is considerably higher than atmosphere which suggests to me that without a charge cooler, one COULD have hot (much less dense) air entering the engine which would negate much of the benefit from pressurizing the air in the first place. Pressurized & hot intake air could improve fuel atomiztion (MPG) and emissions (?) Is this what Chevron means?

I don't think that is what they mean. At least not with the hot air part. I think it is simply that fact that more than enough air aids complete burn in the same way that swirl does: it increases the chances that a hydrocarbon will meet an oxygen.

(2)The increased air mass decreases the fuel-air ratio and, thereby improves the engine's thermal efficiency (fuel economy).

I don't see what they're talking about. It appears to me that they are making an error in using fuel economy as a synonym for thermal efficiency. Maybe my cigarette is in backwards.

Perhaps not really significant to the end of this thread but to the post, I did some calculations just for kicks on the hot air implications.

With an average turbo of 70% efficiency, an intercooler of 60% efficiency, and 80F ambient air,
7lbs. w/o an intercooler is 170F, making 72hp; with, 116F and 75hp.
15lbs. w/o an intercooler is 250F, making 88hp; with, 148F and 99hp.
20lbs. w/o an intercooler is 292F, making 97hp; with, 165F and 113hp.

Hopefully I will soon be able to give empirical results rather than calculations.

[philip]

2) The increased air mass decreases the fuel-air ratio and, thereby improves the engine's thermal efficiency.

I don't see what they're talking about. It appears to me that they are making an error in using fuel economy as a synonym for thermal efficiency.

Yes you do! (efficiency) ... increases the chances that a hydrocarbon will meet an oxygen." I credit the EPA years ago for redefining "efficiency" to mean" how completely combustion occured. Remember all those "smog motors" that were more "efficient" but got lower MPG?

Now the Europeans are hiding MPG under the code name "carbon dioxide emissions" which makes diesel all the more attractive if ... you get a handle on NOx.