Heat Pump on Exhaust

[Occasionally6]

These might be of interest:

Steam ejector based A/C:

Steam Jet Refrigeration Systems:

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Air based cooling:

Nortel Manufacturing - Home of the Minor and the Mega Torch

[IamIan]

@Occasionally6

In an effort to resolve this ... I'm going stay focused and skip the side comments , distractions , etc ... and things that are not directly relevant.

So only ... One thing at a time.

The question at hand from 5 days ago still remains.

Originally Posted by IamIan

Do you have a reference?

So far you have not yet provided a reference that actually backed up the claim of yours in question ... that is what remains in question here.

Do you have a reference that supports your claim that real world automotive engine exhaust always goes supersonic?

Do you have one or not ?

[Occasionally6]

If you can't find any you are not looking. Every discussion of the flow across an exhaust valve covers sonic flow on blow down.

[mort]

Originally Posted by Occasionally6

If you can't find any you are not looking. Every discussion of the flow across an exhaust valve covers sonic flow on blow down.

Hi Occasionally6,
I've been watching this discussion, it looks like a fine example of the Dunning–Kruger effect.

But to help out - this:
Internal Combustion Engine Fundamentals by John Heywood, page 225 in my copy. He even mentions choked flow for intake valves!
But here are two excerpts, one from chapter 6 Gas Exchange Processes



and the other from appendix C.



Everybody knows this, so I thought a discussion of it being just theoretical was amazing.
Now Heywood never says supersonic, or even sonic, he says "velocity of sound" or sometime Mach = 1. In my experience, and probably yours too, when an engineer says "supersonic" they mean speed of sound or higher. Only pedants say sonic - sorry, I see you just did.

-mort

[Occasionally6]

Originally Posted by mort

Hi Occasionally6,
Now Heywood never says supersonic, or even sonic, he says "velocity of sound" or sometime Mach = 1. In my experience, and probably yours too, when an engineer says "supersonic" they mean speed of sound or higher. Only pedants say sonic - sorry, I see you just did.

-mort

Ha ha.

Originally Posted by Occasionally6

Yeah, same thing. If you want to be pedantic, sonic is where the flow velocity exactly matches the local speed of sound, supersonic is where the flow velocity exceeds that speed of sound.

[IamIan]

Originally Posted by Occasionally6

If you can't find any you are not looking. Every discussion of the flow across an exhaust valve covers sonic flow on blow down.

= you don't have one.

A simple 'no' would have saved days of back and forth.

You are completely entitled to your opinion on why you think it always goes supersonic ... I am not interested in trying to change your opinion ... I was interested in if you have a reference to back it up... the reference would have been interesting.

So it seems I have my answer ... no , you don't.

Reminder ... again ... as I said before ... Sonic is not = to your claim of Supersonic ... they are not the same thing.

Originally Posted by mort

Everybody knows this, so I thought a discussion of it being just theoretical was amazing.
Now Heywood never says supersonic, or even sonic, he says "velocity of sound" or sometime Mach = 1. In my experience, and probably yours too, when an engineer says "supersonic" they mean speed of sound or higher. Only pedants say sonic - sorry, I see you just did.

Bold = Exactly my point.

And one more reference that is NOT supporting the claim of automotive exhaust always going supersonic ... if anything it seems to me to refute the supersonic claim.

The discussion about theoretical was not about there being chocked flow or not ... it was about a reference Occasionally6 posted ... that was itself a theoretical case ... one which based the theoretical case partially on an incorrect base assumption about the location of atmospheric pressure in an automotive system ... that was 100% just theoretical.

[jeff88]

Originally Posted by t vago

Heh - my EGR experiment that I did earlier this year took me into the realm of MPGuino. Soon, hopefully, I can go back into EGR.

I remember when you had started this, but missed the continuation of the experiment. A 7.7% increase is definitely well worth it. What caused the hiatus (so to speak) of the experiment?

I found this site, learned a few things... Allpar

I'm wondering, if the EGR decreases the temperature of the combustion, would increasing the EGR amount into the intake mean an even colder combustion (more mass means harder to heat up)? If so, would colder spark plugs be of benefit?

At the end of the EGR section, it says the reason EGR increases FE (among other things) is because it increases the mass on the piston, helping to force it down. I wonder if the reason why pgfpro's turbo helped increase mileage was because it helped increase the pressure on the piston, forcing it down against the vacuum.

[t vago]

Originally Posted by jeff88

I remember when you had started this, but missed the continuation of the experiment. A 7.7% increase is definitely well worth it. What caused the hiatus (so to speak) of the experiment?

I stopped gathering data points when I found that the UltraGauge was not reading my fuel savings correctly with the EGR mod in place, after I had spent a month calibrating it to accurately report FE. In fact, it continues to read really low even now. I'll fill up, calculate my tank FE at 24 or 25 MPG, and the UltraGauge will faithfully (?) report that I got 21 MPG. I don't want to have to continually recalibrate the dumb thing, every time I make an engine modification, so I went with the MPGuino instead to measure fuel economy. (the EGR mod is still in place - I'm not going to remove something that is saving me money)

Along the way, I had to modify the MPGuino source code a bit, to account for Chrysler's peculiar fuel pressure regulation, among other things. However, now that the code is (finally) more-or-less stable, I can resume my EGR experiment.

Originally Posted by jeff88

I found this site, learned a few things... Allpar

I'm wondering, if the EGR decreases the temperature of the combustion, would increasing the EGR amount into the intake mean an even colder combustion (more mass means harder to heat up)? If so, would colder spark plugs be of benefit?

Maybe. The only way to know for certain is to look at the plugs after doing a run with increased EGR, and see if they show signs of being overheated. I doubt the plugs will be overheated, though.

I like reading through AllPar, too. They have some really nice tidbits of information there.

Originally Posted by jeff88

At the end of the EGR section, it says the reason EGR increases FE (among other things) is because it increases the mass on the piston, helping to force it down. I wonder if the reason why pgfpro's turbo helped increase mileage was because it helped increase the pressure on the piston, forcing it down against the vacuum.

That's one way to state what is happening. Some members here will state that peak cylinder combustion pressure will have increased, while others (like me) will state that intake manifold vacuum will have been lowered. Both will contribute to more efficient gasoline engine operation.

[RedDevil]

Originally Posted by t vago

(EGR affecting FE) ... others (like me) will state that intake manifold vacuum will have been lowered. Both will contribute to more efficient gasoline engine operation.

+1.
That's what my UG shows at least. The reported engine load % is about equal to the intake manifold pressure in kPa, until the EGR becomes involved; then the intake pressure rises, lowering pumping losses for the same load %.

[serialk11r]

Originally Posted by jeff88

I'm wondering, if the EGR decreases the temperature of the combustion, would increasing the EGR amount into the intake mean an even colder combustion (more mass means harder to heat up)? If so, would colder spark plugs be of benefit?

At the end of the EGR section, it says the reason EGR increases FE (among other things) is because it increases the mass on the piston, helping to force it down. I wonder if the reason why pgfpro's turbo helped increase mileage was because it helped increase the pressure on the piston, forcing it down against the vacuum.

NO no no. EGR decreases the temperature of combustion because there's less fuel. Since there's less combustible mix, it's actually harder to ignite. Colder spark plugs won't do you any good.

EGR increases the mass of gas but that doesn't do anything. You need pressure. EGR is only to dilute the intake mix so you need to suck in more of it (which takes less energy because the engine has constant stroke volume and the energy to create the manifold vacuum is by far greater than the energy required to accelerate the air down the intake tracts). If it's not cooled EGR, the charge starts out hotter and you lose efficiency from that, but gain most of it back from the pumping loss reduction.