Pumping losses

[R.I.D.E.]

Gentlemen, I though when came here to post there was a group of people who were concerned with obtaining the best efficiency in their cars.

I have suggested a very simple test to prove my point, and I am surprized at some of the answers.

Is it too hard to do a test?

You wouldn't be worried about your statements that basically say pumping losses are greater at highest vacuum, being proven to be incorrect and you may have to rethink your own logic, Nah, just be insulting and tell me I am a moron.

I guess that will change the Laws of Physics to suit your false opinion.

Simple Physics boys and girls, the more you pump the greater the losses.

Do the test and then come on back and argue why open throttle will slow your car down more quickly.

That will certainly change the laws of Physics.

Tell me I am an idiot and I need to read a book.

I am sure that will change the laws of Physics.

Tell me there is no energy loss in reciprocation, none in compression, but all of its in creating vacuum, even though you can never create a perfect vacuum in any engine. When faced with the invalidity of your claims rationalize your way around the fact with the statement that compression losses are recovered by combustion.

Once lost it isn't recovered, thats why 2/3 rds of the energy content of the fuel is wasted. No physical action that involves any energy cost in creating the necessary components for the combustion stroke is ever recovered, period, with no exceptions.

Dont believe me for a second. Insist of absolute proof.

Do the test and prove it for yourself, then you have a fact you can state in a courtroom under oath, not the opinion of some fool you never met, and understandably shouldn't believe with out proof.

If you want maximum efficiency you have to get all the air in the cylinder that is possible, that is maximum efficiency. the only other factor is engine speed. Every engine has an optimal speed where the maximum air and fuel charge delivers maximum horsepower for the volume of fuel consumed.

If you think WOT with the corresponding enrichment is necessary at engine speeds of 1000rpm you are wrong.

I recommended another simple test to prove this.

Hook up a vacuum guage and with the vehicle in top grear depress the throttle only far enough to obtain your minimum vacuum reading.

Guess what Boys and Girls, at 1000 rpm it will not be 100%, or 75%, or even 50%. The engine only needs 1/6th the air it needs at max rpm.
Are we now going to argue the details about whether its 1/6th. or maybe 1/7th, or maybe even 1/5th.

Bottom line it ain't WOT, it aint even close to WOT, if the WOT you are talking about is as far as the throttle butterfly will move.


regards
gary

[theholycow]

Originally Posted by monroe74

On the other hand, you might discover that your current monitoring system has no major lag, and your ECU is itself inducing the lag, for whatever good or bad reasons.

I think I have discovered that. Today I looked through the logs, which are plain CSV files with all the data gathered, and I'm actually having some difficulty understanding when/why it goes open loop, but it's almost definitely not a matter of when I floor the pedal.

Interesting. At what point did you hear the beeps? What was the position of the ignition key at that moment? Was the engine running? Car in motion? Just curious.

I put it in neutral, turned the key off, coasted a second or two before I remembered that I'd need the key on, turned the key on, continued coasting, turned the key to start then let it go back to "On", and that's when it gave me the beeps in a common error pattern. They were not a normal set of beeps, not seatbelt or routine related, they were obviously error beeps, three long beeps with short-medium length silence between. My Vag-Com cable is broken, once it's repaired I'm going to try it again with the cable hooked up and see if I can get any data. At the same time I'll try recording the beeps to play back on forums for people to help.

Folks on the VW forum were too busy morally judging me for EOC to help me understand what the beeps meant.

I do not bump start because I'm pretty sure the manual specifically says not to. I am out of my comfort zone with this lease; I'm not used to leasing, and I'm being very careful. I've always owned and never been in warranty for long, so I've usually had more freedom.

Originally Posted by monroe74

Assuming that the engine is being turned by an outside force, why is there more loss at WOT? I think you and Gary have both tried to explain this, but I understand neither explanation.

I've only partially been following that portion of the thread, but I think better language to use would be that engine braking at WOT would be more, which I suppose could make sense -- with the throttle plate open it could pull more air in before the compression stroke, then of course in the compression stroke the valves are closed so throttle doesn't matter to that cylinder when it's compressing.

A random bit of news: I tried P&G in my automatic v8 pickup today and it was way easier and less work than in the manual car. There's lots of fear on this forum for people with automatics to do P&G, but I'm more comfortable than with the manual, where I fear excessive wear on the clutch and synchros.

[monroe74]

Originally Posted by R.I.D.E.

Is it too hard to do a test?

Yes. I live in a densely populated area where it's not that easy to find a deserted road that lends itself to a series of coast-down tests. If I had a landing strip in my backyard, that would be another story.

Also, I don't like the idea of putting my motor through a lot of revs when it's not running. Yes, I realize this is what I do every time I use the starter (but that cranking speed is much lower, and the duration is very short). And yes, I understand that the oil pump is mechanical. But your test still means I'm doing something to my motor (and transmission) that the engineers didn't imagine I would ever do, and I would rather not discover various unintended consequences.

And speaking of doing tests, I want to again encourage you to hook up a cheap DMM, and then your lean burn claims will be based on measurements instead of assumptions.

Do the test and then come on back and argue why open throttle will slow your car down more quickly.

That appears to be a Freudian slip. "Open throttle will slow your car down more quickly" is exactly the claim you've been making.

Tell me there is no energy loss in reciprocation

Of course there is energy loss in reciprocation, but that loss is the same regardless of throttle position. So I don't know why you're tossing in that red herring.

Tell me there is no energy loss ... in compression

There is indeed very little energy loss in compression, because the compressed air is simply the equivalent of a spring. The energy I put into it on the compression stroke is returned to me on the power stroke.

But aside from that, this is yet another red herring, because the presence or absence of an energy loss in compression is an entirely separate matter from the question of whether or not a closed or open throttle is more efficient.

Tell me there is no energy loss in reciprocation, none in compression, but all of its in creating vacuum

This is called using a straw man argument. I have not claimed that "all of its in creating vacuum," and that there are no other losses (like mechanical friction, for example). I have only claimed that an open throttle is more efficient than a closed throttle. It would be better if you responded to what I've actually said, rather than what you are imagining I've said.

even though you can never create a perfect vacuum in any engine

Yet another straw man. I have not claimed that we're creating a perfect vacuum. We're not. But we are creating a vacuum, relatively, and that's a waste of energy.

When faced with the invalidity of your claims

I'm fully prepared to find out that my claims are invalid, as soon as I see proof that they're invalid. But that hasn't happened yet.

When faced with the invalidity of your claims rationalize your way around the fact with the statement that compression losses are recovered by combustion.

The subject of compression 'losses' is a red herring, as I've pointed out. But for the sake of clarity I want to point out that I didn't claim that "compression losses are recovered by combustion." Compression losses are recovered even in the absence of combustion. Even if the ignition system is off, and no fuel is entering the engine, and the engine is being spun by an external force, then there are still virtually no compression losses. Why? I already explained why: the compressed air acts as a spring. When I compress air on the compression stroke, I'm not consuming energy. I'm just storing it in the form of compressed air. And combustion is not necessary to get the energy back.

Dont believe me for a second. Insist of absolute proof.

It's true that I don't believe you, and I am insisting on proof, and I'll be waiting patiently, hoping that you provide some.

If you think WOT with the corresponding enrichment is necessary at engine speeds of 1000rpm you are wrong.

I don't know what you mean by 'necessary.' And anyway, that's not what I said. What I said is that WOT, at 1000 rpm or at any other engine speed, minimizes pumping losses and optimizes BSFC (assuming you're not inducing open-loop, which does not happen on the wideband-sensor cars we're discussing).

The engine only needs 1/6th the air it needs at max rpm.

Even though the engine needs less air, it turns out that pumping losses are still a major factor. Please take another look:

http://www.autospeed.com.au/cms/gall...0&a=110216&i=6

The value (in BSFC terms) of using WOT, instead of 25% or 50% throttle, is actually much greater at 1000 rpm, compared with 2000 rpm or 3000 rpm. Nevertheless you're suggesting that at 1000 rpm, WOT is pointless, because the engine doesn't need much air. Maybe you can help us understand why the graph is wrong and you're right.

[monroe74]

Originally Posted by theholycow

they were obviously error beeps

Hmm, I'm stumped. I can see why you're not that eager to try EOC again. Anyway, I think you're still getting a lot of value by just coasting in neutral.

engine braking at WOT would be more, which I suppose could make sense -- with the throttle plate open it could pull more air in before the compression stroke, then of course in the compression stroke the valves are closed so throttle doesn't matter to that cylinder when it's compressing.

OK, you're saying the engine has less work to do if there's less air to compress. If you close the throttle, there's less air to compress, so the engine is doing less work. But if that's true, then imagine going a step further. Imagine if on the intake stroke, instead of the intake valve being open, you had a way to magically slam it shut, for the duration of the intake stroke (during the engine-braking scenario we're discussing). So now the piston is traveling down, and all the valves (in that cylinder) are closed. You are now asking that piston to create a vacuum in that cylinder. That's a lot of extra work.

Next comes the compression stroke. True, this is easy, because the piston has atmospheric pressure below it, and a vacuum above it. So you get back the energy you supplied creating a vacuum on the intake stroke.

Trouble is, you're not done. Next comes the power stroke. At this moment in a normal cycle, above the piston would be a bunch of compressed air. But since we took in no air during the intake cycle, there is now no air in the cylinder. As the piston travels down on the power stroke, we are creating a vacuum again, doing a lot of work. And this work is not returned to us in the next stroke. As soon as the power stroke is done, the exhaust valve opens, and air rushes in to fill the vacuum. And now we have to pump that air out, during the exhaust stroke. And it doesn't help that the air is reciprocating; as soon as it rushes in, we have to get it to reverse direction and rush back out.

Closing the intake valve entirely (during the intake stroke) is just a more extreme version of having a closed throttle. But I think it helps to illustrate what's going on. And even though we're discussing engine braking, the pumping issues during normal operation are essentially the same.

When you look at both scenarios (lots of air entering during intake, as compared with less air, or no air, entering during intake), you realize that restricting the amount of air helps you during the compression cycle, but you pay for that twice: both during the intake stroke, and the power stroke.

In other words, it's true that a closed throttle reduces the amount of engine braking that takes place during the compression stroke. Trouble is, it increases the amount of engine braking that takes place both during the intake stroke, and also during the power stroke. The net of this is that closed throttle increases engine braking. You have to look at all four strokes to understand why.

There's lots of fear on this forum for people with automatics to do P&G

P&G is generally difficult with an automatic, because what you want is high throttle at low revs. But most automatics will downshift when you give them high throttle.

[R.I.D.E.]

Uh Monroe,

The graph you have linked to is a graph of loads NOT THROTTLE POSITION.

To maintain a specific load percentage, typically using a hydraulic "brake" on a dyno, you have to adjust the power output to match the load perfectly. If not the engine speeds up or slows down.

In other words you have to pick the throttle position to match the load, and only one throttle position will accomplish a percentage sustained load.

At 100% load your throttle position is exactly where the rpm will neither rise or fall, but even then IT is NOT at WOT. Its WOT at maximum rpm and highest sustainable load, which is also the maximum rated horsepower of the engine

WOT will make engine speed rise until you have reached the maximum power output the engine can sustain which is the rated horsepower and max rated load. No less that 100% load can be maintained with WOT.

You cant even test loads below that with WOT because WOT will take the engine to maximum power, at the rpm where that is achieved.

You need to check the graph the uses 25%, 50%, and 100% throttle positions with the load being the variable.

At 1000 rpm the difference is a couple of percentage points due to enrichment, but basically the three graphs merge at 1000=1500 rpm.

If that graph is the basis of your argument (the one you linked) you are simply using the wrong graph.

If thats also the basis of all your arguments the foundation just dissolved under your building.

regards
gary

[R.I.D.E.]

Also:

The identical graph you referred to in your link is a part of a number of graphs and maps in a link provided by Road Warrior in the HHO thread in this section of this forum.

You can find it by googling "autospeed brake specific fuel consumption"

In the group of graphs and maps there is a graph that illustrates horsepower generated at 25%, 50% and 100% throttle openings. These graphs clearly illustrate the convergence of the three positions at speeds between 1000-1500 rpm.

Further down there is a map of the insight engines Brake Specific Fuel Consumption, which clearly illustrates the effects of lean burn at low engine speeds. Believe it or not that shows the effects of lean burn, as well as the less efficient BSFC at engine speeds lower than 1200 rpm.

The VX lean burn is more robust than the insight, and the only place on the insight map that shows better BSFC is at engine speeds above 3000 rpm, where the VX does not reduce the valve lift of one intake valve to improve swirl and fuel consumption, utilizing the lower valve lift and higher AF ratios, both essential components of lean burn.

I have a DMM and I might even check to see that I am maximizing the lean burn map of the VX to improve my overall 57 MPg average.

As I said before I use the upshift light to apply throttle just enough to keep the light off and sometimes I shift from 3rd to 5th. In most cases the light never comes on because I keep the throttle position above the threshold where the light will come on, knowing when the light comes on the manifold vacuum is too high for maximum efficency.

Whether you choose to believe it or not is irrelevant to me.

I have tried to present my opinions and observations, and offered methods of proving those hypotheses.

The ultimate proof is in the mileage figures I have posted. It's easy to write the mileage down on the fuel reciept.

It's unfortunate that your situation does not provide comparable opportunities to achieve the best possible mileages.

Mine provides me with constant opportunities, with at least 4 different routes to the same destination and back, with excellent opportunities for hypermiling.

You know the method, you know the mileage, and you know my operational tactic. Another advantage that makes a direct comparison of mileage unfair is the extremely low mileage of my VX.

Believe it or not I hope your testing provides me with information that allows me to improve my mileage even further.

Monitoring the sensor voltage output which if memory serves me is about .45 tp .5 volt for lean burn will help me refine my driving and throttle position to increase my percentage of lean burn utilization.

I think the person who posted those voltage figures also said it was about the same if you disconnected one of the injectors.

The original intent of my posting this thread was to see if people understood the many different sources of losses that are dumped into the term "pumping losses". Understanding sources of all losses in reciprocating engines is an essential component of reducing or eliminating them to the greatest extent possible, which is one of the core principles of my engine and powertrain design whcih is unthrottled and allows significant reductions and in some cases elimination of reciprocation losses, cooling system losses, oil pump losses, valve train losses, separate intake and exhaust manifold harmonic losses, etc, etc.

I worked for Mercedes in 1981-82 when they eliminated the throttle on their diesel engined cars. When they did they had to add a vacuum pump to control the heating and air conditioning as well as the door locks that were vacuum operated. The vacuum pump ran off the same drive that ran the injection pump.

Mercedes stated that eliminating the throttle butterfly improved efficiency by 7%.

Good luck in you research and investigation.

regards
gary

[monroe74]

Originally Posted by R.I.D.E.

At 100% load your throttle position is exactly where the rpm will neither rise or fall, but even then IT is NOT at WOT. Its WOT at maximum rpm and highest sustainable load, which is also the maximum rated horsepower of the engine

We're discussing the word "load" because it appears on this graph: http://www.autospeed.com.au/cms/gall...0&a=110216&i=6

I think there's some confusion about what the word load means, in the context of that graph. "100% load" doesn't mean "your throttle position is exactly where the rpm will neither rise or fall." That makes no sense whatsoever. If I'm traveling at a very moderate, steady speed, with a very moderate throttle opening, I can very easily be in a situation where my "throttle position is exactly where the rpm will neither rise or fall." But that doesn't mean I'm at 100% load.

100% load generally corresponds with WOT. And this is indicated in the article that contains the graph we're discussing. The article is here: http://autospeed.com/cms/A_110216/article.html

The article says this: "At 100 percent load (ie wide open throttle) ..."

Please note this reference: http://www.motorera.com/dictionary/FU.HTM#FullLoad

Which says this:"Full load: An engine operating conditions where the accelerator is fully depressed, i.e., the throttle is fully open, which does not necessarily mean high engine speed"

Please also note this reference: http://members.rennlist.com/pbanders/djetfund.htm

Which says this: "Full-Load: When the engine is under full-load (wide open throttle) conditions"

I could continue, but that should suffice.

I said 100% load generally corresponds with WOT, because the two things are often considered interchangeable, but according to a more technical definition, they are not exactly the same. A more technical definition of load is this: the ratio of gas moving through the motor, at this instant, compared with the theoretical volumetric capacity of the motor, at the current rpm.

So load increases as throttle angle increases, but in the strictest technical sense, 100% load does not always correspond with 100% throttle. Here's one example. An engine that uses a form of forced induction (e.g., a turbo) would typically have a load greater than 100%, at WOT. That's because the turbo is forcing extra air through the motor, compared with the calculated result you would get if you multiplied the static displacement times rpm. At the other extreme, an engine with a very inefficient and poorly designed intake manifold would never achieve 100% load, even at WOT.

That's explained here: http://www.cartechbooks.com/vstore/s...6&chapter=9415

That article says this: "Wide-open throttle operation for naturally aspirated engines results in a load anywhere from 60% to 105%, depending on how efficient the intake, camshaft, and cylinder designs are. Supercharged engines routinely see loads in excess of 100% once boost is present in the manifold."

This is closely related to the concept of volumetric efficiency: http://en.wikipedia.org/wiki/Volumetric_efficiency

"WOT will make engine speed rise ... WOT will take the engine to maximum power"

That's a truly astonishing statement. WOT will only make engine speed rise if the engine, at current rpm, is producing more than enough power to overcome whatever level of drag is currently being placed on it.

Anyway, I hope you'll tell us what you mean when you use the term "load," since your use of the term is different from what I've become accustomed to, via sources other than you.

[monroe74]

Originally Posted by R.I.D.E.

Further down there is a map of the insight engines Brake Specific Fuel Consumption, which clearly illustrates the effects of lean burn at low engine speeds.

The article you're talking about is here: http://autospeed.com/cms/A_110216/article.html

The graph you're talking about is for the Insight CVT, which did not have lean burn. The article itself indicates this.

Believe it or not that shows the effects of lean burn

I'm afraid not.

[theholycow]

Originally Posted by monroe74

Hmm, I'm stumped. I can see why you're not that eager to try EOC again. Anyway, I think you're still getting a lot of value by just coasting in neutral.

I definitely am. I'm really groping around in the dark here until I fill up, but I'm looking at anywhere between 2 and 10 mpg increase. Why oh why can't my 2008 VW have a couple pieces of inexpensive technology that were in my 1987 Cadillac, when it's already got so much more other more expensive technology? That car had a digital gauge that could display instant and average MPG, gallons to empty, or miles to empty. It also did loads of other cool troubleshooting/realtime data acquisition stuff...

OK, you're saying the engine has less work to do if there's less air to compress. If you close the throttle, there's less air to compress, so the engine is doing less work. But if that's true, then imagine going a step further. Imagine if on the intake stroke, instead of the intake valve being open, you had a way to magically slam it shut, for the duration of the intake stroke (during the engine-braking scenario we're discussing). So now the piston is traveling down, and all the valves (in that cylinder) are closed. You are now asking that piston to create a vacuum in that cylinder. That's a lot of extra work.

Eek! I didn't want to get sucked in to this discussion, but I can't leave stuff unsaid. I don't entirely understand what this discussion is about or where it came from, only a few of the specific technical bits that are being discussed.

Again, to clarify my understanding of what's being discussed, it would best be demonstrated with the fuel cut off, the engine not running but merely used for engine braking, and the question is the difference between closed and wide open throttle.

I saw this somewhere, and I don't remember if it was in this thread, another thread on this forum, or another forum entirely. I think it was in one of the DIY DoD threads. Anyway, what I saw is a very good explanation of energy losses when you close the intake and exhaust valves: Whatever amount of air is in there becomes a spring. As much energy is spent compressing it on upward strokes, is given back on downward strokes. The only energy lost is friction and general losses to such things as reversing the direction of the piston, which you'll have under any conditions where the engine is spinning.

Sure enough, GM's latest attempt at DOD, called AFM (Active Fuel Management), closes all the valves for each deactivated cylinder:

Originally Posted by http://en.wikipedia.org/wiki/Active_Fuel_Management

In order to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake valve is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another.

When you look at both scenarios (lots of air entering during intake, as compared with less air, or no air, entering during intake), you realize that restricting the amount of air helps you during the compression cycle, but you pay for that twice: both during the intake stroke, and the power stroke.

You forgot a stroke.

P&G is generally difficult with an automatic, because what you want is high throttle at low revs. But most automatics will downshift when you give them high throttle.

I didn't think that P&G necessarily required reducing pumping losses during the pulse, and others report P&G working with high RPMs. Here's where I think P&G really gets its savings:

When you're just cruising along with a mostly closed throttle, you have to feed fuel to keep the RPMs up to cruising speed. You have mainly pumping losses and not much power being generated, AND you are probably spending extra fuel just to spin the engine at enough RPM to NOT do any engine braking. This is especially true when you're going downhill. I was really in the zone when I was thinking about this while driving yesterday, and I lost some of it since then, but I think I retained enough.

So, If your pulse is a little wasteful due to uneconomical gear choice by the automatic transmission, it's still better than cruising along using fuel just to spin the engine.

[R.I.D.E.]

Things make no sense to you because you need more knowledge, or maybe a more detailed explanation.

Another misquote and you avoid explaining the partial load throttle positions, because they require the same precise throttle control to maintain the load at a specific rpm.

You also fail to understand that a load beyond 100% can be applied, then you try to add forced induction into the mix, which has not been part of this thead.

But since you insist, applying a load beyond the engines 100% capacity, (without the addition of forced induction) means the load is unsustainable and the engine will slow down since it can't maintain the load applied at the rpm selected. Pick your throttle position it doesnt matter, rpm is unsustainable at over 100% load.

Its like climbing a mountain son. If your gear choice is too high and the grade is too steep your speed is not sustainable. In order to increase your speed you must choose a lower gear that matches your engines WOT max power with a gear ratio that allows you to maintain a higher speed up a the grade.

It might make more sense if you don't understand something, just ask for a more thorough explanation .

regards
gary