Pumping losses

[monroe74]

"Scenario 2 has no suction losses since you have WOT."

Earlier you said this: "3. Decelerate using same shift points as 2 with accelerator at WOT." I think you're getting your numbers mixed up. That's one reason I'm finding your example hard to follow, but it's not the only reason.

Anyway, I think your example reduces to the following much simpler comparison.

A) Take an engine that's not running, and spin the crankshaft, with the throttle closed.
B) Take an engine that's not running, and spin the crankshaft, with the throttle open.

I think you're claiming that A takes less work than B. Really?

"your conclusion about WOT operation assumes the BSFC map for a VX is identical to a map for a non lean burn engine"

No, I'm not claiming it's identical. I'm just claiming that there's enough similarity to make for a worthwhile comparison.

"the map you are using as a reference is not a VX engine map"

True. But I think it's helpful, as compared with using no map at all. If you have a map or reference that you think is superior, I hope you will give us a chance to see it.

I think it's clear that it's possible to save gas by utilizing lean burn, and it's possible to save gas by minimizing pumping losses. The interesting thing is that it's just not possible to do both of those things at the same time. Lean burn is generally associated with relatively small throttle settings. Trouble is, small throttle settings are generally associated with large pumping losses. Therefore it's necessary to make a choice. And the right choice probably depends on the immediate situation.

P&G is a technique that relies on relatively large throttle settings. And there seems to be lots of evidence that P&G works (and I think it works primarily by minimizing pumping losses). Trouble is, P&G is basically incompatible with lean burn, because in the pulse phase, you're accelerating. It's generally possible to maintain lean burn while at a steady speed, but not while accelerating. So we're back to that choice again, to either minimize pumping losses, or maximize lean burn. I have a hunch that the former strategy is more effective, when driving conditions allow for P&G (ideally in the range of 25-45 mph, I think). When driving conditions require a steady speed (especially at higher speeds, like 50+), then my hunch is that it makes sense to maximize lean burn. I'm not sure about this, and I'm open to evidence that I'm wrong. But I just haven't seen that evidence yet.

"Check your BSFC map at 50 % compared to higher throttle opening positions AT LOW ENGINE SPEEDS"

I have. It shows that WOT is more efficient than 50%. Not always by a wide margin, but nevertheless the margin is positive. Therefore it's probably worth taking. It also shows that at 1000 rpm, the margin is actually quite large. And 1000 rpm/WOT is a state I use quite frequently.

"You also assume that WOT is preferrable to 70%"

True, I do. I don't believe the margin is always large, but I believe the margin is always positive. That's what I see on the graph we're discussing. On the other hand, I think you assume that 70% is always preferable to WOT. I'm open to believing this, but so far I've seen no proof.

"You also choose to ignore the fact that if you maintain lean burn you are using about 60% of the fuel you would use at WOT"

I think the number might be even less than 60%. But what's more important than the air/fuel ratio is the work/fuel ratio. In other words, it's important to approach the analysis in terms of BSFC, not absolute fuel consumption.

"Thats why I use less than 50% throttle position, because I can pulse quite a bit longer for the same amount of fuel which increases the total distance of one P&G cycle."

If I understand correctly, you're using P&G, and you're claiming that you're in lean burn during the pulse phase. May I ask how you know? My experience using a DMM to monitor my O2 sensor leads me to believe that lean burn generally does not occur during acceleration, even mild acceleration. And this is consistent with the comments of others who have monitored lean burn in this manner. How are you monitoring lean burn?

"I use the sil indicator to determine throttle position when I accelerate. It takes me 13 seconds in 5th gear to accelerate from 50 to 65 MPH, so you can duplicate that time and know exactly the amount of throttle I am using."

I'm very confused by that paragraph, because the SIL is off 100% of the time that you're in 5th gear, regardless of vehicle speed, engine speed, or throttle position.

"I only pulse in 4th gear when my initial speed is below 30 MPH and the light never comes on during the pulse."

If you are in any gear other than 5th, and using a throttle setting large enough to keep the SIL turned off, then you are almost certainly not in lean burn.

[R.I.D.E.]

The source of my assumptions is what I read in this forum, that doesn't make it a fact any more than everything you read in any book makes it a fact. Its all hypothetical until real testing proves otherwise. Try the throttle closed versus open test that I suggested. If you coast down distance is lower with throttle open I am correct (more resistance at WOT). If it is lower with throttle closed you are correct (more resistance at closed throttle). The reason I think I am correct is because compression is greater at WOT, while suction losses are insignificant at WOT. A simple test that proves my point.

I have done thousands of compression tests and the conclusion I have reached is the cranking speed is lower with WOT. My reasoning to support that is simple. You are pumping more air through the engine at WOT, because the compression is lower if you don't open the throttle. Since suction losses are practically nil at WOT I can't rationalize any other conclusion.

Please let me know the results of your test.

Think about the Jake brake on big rigs, they are using trapped compression, not vacuum, obviously they can't use vacuum. The difference in compression versus vacuum is directly proportional to the compression ratio. No closed throttle will produce a perfect vacuum, but in my previous example with 185 pounds of compression you have over ten times the resistance that 14.7 negative pounds of vacuum would ever produce.

I wish I could prove when lean burn is engaged. Since that is not possible I rely on those contributors to this forum who have developed a means of proving that it is engaged when climbing a slight grade in 2nd, 3rd, 4th, and 5th gears. In fact in the links Tom O proivided there is information that justifies that assumption. The contributor was one of the hypermilers that was involved with Wayne Gerdes, who made the statement that lean burn was possible in lower gears and climbing grades.

"You can climb a slight grade and still stay in lean burn, even in lower gears".
The use of lower gears would indicate to me that steeper grades would still allow lean burn as long as you used lower gears.

Think of it this way, we know the VtecE closes one valve almost completely to create swirl and improve low speed fuel air mixture (below about 2500 RPM). Homogenous Charge Compression Ignition relies on close to perfectly even distribution of the fuel particles in the fuel air charge. Testing has shown that this creates the potential for compression ignition of gasoline with a 25% improvement in efficiency.

You can check that by googling HCCI. The problem is its presently not possible to accomplish HCCI over all the loads and ranges of normal engine speed. I takes some time for the mixture to completely emulsify which brings on the problem of having a fairly significant amount of fuel air mix in the manifold, which would be a scary thing if you had a backfire. One solution is ultra high injector pressures, but it may be that it will not be possible with fuel injection occuring soo close to the intake valves. We may actually have to go back to a form of throttle body injection with mechanical turbulence and preheating of both air and fuel to allow better fuel particle distribution and to offset the fact that when vaporized fuel tends to become cooler. In the carb era without preheating of the air in cold temps you had carb icing where the fuel would not suffeciently atomize. The result was hesitation to the point of stalling. Its the same principle as warm air intake which while reducing the mass of air going in the engine also allows for better atomization of the fuel particles. Preheating the fuel would also help, but when the fuel is heated you risk vaporizing the fuel in the lines which causes serious problems.

My position is lean burn requires better atomization in order to function at 22-1 AF ratios. While it is not true HCCI at certain speeds and loads it is at least a significant step towards HCCI.

We disagree on when lean burn is actually occuring. I am at a disadvantage with my old time pre computer education which ended in the late 60's. The shift indicator light is there to tell you when to shift for best economy. To me it makes no sense that the light would be on when lean burn was working but off when it wasn't. The light uses several imputs, but basically it is telling you your vacuum is to high for efficient operation. Thats why I believe (can't prove it other than my mileages) that lean burn occurs if you stay just above the point where the light comes on and below 2500 rpm. Of course the light does not come on in 5th gear, but you can still use the same throttle position percentage. It doesnt take much throttle to accelerate from 50-65 in 5th gear in 13 seconds. The coasting time is about 17 seconds,and it may be better to just forget P&G at those speeds. Other forum members have also stated that it is difficult to achieve the percentages of improvement in average mileage with a VX, compared to the same year vehicle without lean burn. Thats easy to understand when you look at the difference in combined mileage for both vehicles with the difference about 33%.

I enjoy civilized debate and hope to learn from our interaction. It certainly is possible that your position is correct and mine is less correct.

I don't think a "I am totally right and you are totally wrong" position would produce any learning.

regards
gary

My rationale is based on this statement by a fellow hypermiler who apparently has a means of verification.

"I can maintain lean burn up to 70 MPH"

TomO stated that lean burn is a function of several imputs one of which is the load placed on the engine.

If I use the same throttle position as I would at a constant 70 mph, I should be able to stay in lean burn. At lower speeds that means you would be accelerating since total energy losses are lower at lower speeds maintaining the same load would allow for acceleration.

If the potential for lean burn did not exist, I would only disagree with you on the throttle position. In that case I would use 75% because at WOT you are creating enrichment that doesn't exist at 75%.

If you looked at a BSFC map for the VX (even though I don't know where on is or I would provide a link) it would be two maps.

One in lean burn

One outside of lean burn

Combining the two would be confusing to say the least.

This is what I believe. Mr Honda was a pioneer in lean burn technology, going back to the stratified charge prechamber CVCC engines in the 70's. He died in 1991 the year the first VX was produced. He was not a highly educated man, but his intelligence is unquestionable. After his death the driving force behind lean burn technology seems to have been gradually lost. Combined with increasingly stringent emissions requirements lean burn fell out of favor, principally due to NOX emissions.

Lean burn was a way of compensating for the poor BSFC of normal engines when there is any significant throttle restriction ,and it was a practical solution that proved to be more economical.

Try one more test.

Hook up a vacuum guage and see how little throttle opening you can use to achieve the lowest possible vacuum reading at low engine speeds. I beleive the throttle opening percentage would be below 25%, because you are only running the engine at about 1/5 of maximum speed (give or take).

I believe the sil light uses vacuum as its principle imput (not the only imput), to show the driver when upshifting will create a greater load and lower vacuum to produce the same work, which I think we can agree is more efficient.

regards
gary

[dosco]

Originally Posted by R.I.D.E.

I believe the sil light uses vacuum as its principle imput (not the only imput), to show the driver when upshifting will create a greater load and lower vacuum to produce the same work, which I think we can agree is more efficient.

I think this brings up a good point. Note that the SFC chart indicates when the engine is operating at maximum efficiency. This is not the same as operating at minimum rate of fuel flow. This explains why at certain load+RPM combinations (e.g. optimum efficiency on the BSFC graph), the engine is burning more fuel than at idle (note comments by Pale in other threads about fuel use at idle).

I understand the concept of SFC, but after a few tanks of gas and use of P&G but no ridiculous improvements in fuel mileage, I was wondering what the hell was going on. Then it occured to me that the isopleths on the BSFC graph (that I was trying to emulate in my P&G technique) are of fuel flow rate per hp produced. Which I had read but didn't "compute" in my mind.

I can't directly determine what the BMEP of my engine is at any given time, so I goto the SFC vs RPM chart with the load curves. I was able to find a dyno run for a 4 cylinder Camry (believe it or not), so to get an idea of fuel flow rate I plugged in the hp number for given RPM numbers for different load lines. Lo and behold that at less-than-ideal RPM and throttle settings, I can easily reduce the rate of fuel flow. In other words, at 2,000 RPM on the 50% load line I can use less fuel per hour than at 2,500 RPM at 100% load.

Therein lies the point - to minimize fuel use. I can maximize efficiency by operating in certain load+RPM combinations, but in doing so can actually use more fuel in total. And the point is to use the least amount of fuel for the most amount of miles - this is why idling (which is less efficient) can improve you rmileage.

I'm not sure I can hit crazy MPG numbers by worrying about throttle angle and RPM alone - the other variable is the HP created. This defines the fuel used.

<sigh>

I think I need a scangauge.

[theholycow]

Originally Posted by dosco

I'm not sure I can hit crazy MPG numbers by worrying about throttle angle and RPM alone - the other variable is the HP created. This defines the fuel used.

<sigh>

I think I need a scangauge.

Unfortunately, as I found out in another thread, the SG doesn't actually measure fuel flow and some of the other important variables it displays. Instead, it calculates them. Be aware of that as you consider buying it for precision measurement of such things.

[dosco]

Originally Posted by theholycow

Unfortunately, as I found out in another thread, the SG doesn't actually measure fuel flow and some of the other important variables it displays. Instead, it calculates them. Be aware of that as you consider buying it for precision measurement of such things.

Fair enough, but the next logical question: what device out there actually measures fuel flow in passenger cars?

[monroe74]

Originally Posted by theholycow

Just a guess.

I think you're good guesser.

please use the built-in quote feature

Sorry, I know I'm a major offender in this regard. I should realize it's probably annoying. I'm just so used to doing it the old-fashioned way, but I'll give it a try.

I'm avoiding open loop.

OK, that's what I figured. Thanks for explaining; I think you explained it very well.

I think one of the interesting things about open-loop is that it's something my car generally doesn't do, as far as I can tell. I think a characteristic of wideband-sensor systems is that open loop occurs only when the engine is cold, or when there's some kind of a sensor failure.

But I understand why avoiding WOT makes sense in your situation.

I can't tell if it's lagging a few seconds in its readings or if it really doesn't go into open loop easily

Interesting question. I don't know what that lag is about. With my DMM, I can monitor my O2 sensor directly, and the response is immediate. That is, I can see AFR changing right away, as I move the throttle. But you're reading info indirectly, with Vag-Com getting the data from your car's computer in OBD format (I think that's how it's working; I could be wrong). That's a more complicated process, so it's harder to tell where the delay is being introduced.

Coming out of open loop, I could see how your car's brain (ECU or ECM or whatever VW calls it) could choose to lag and hold open loop for a few extra seconds, for good reasons. But I would think that going into open loop would be immediate, when you floor it under certain conditions. After all, the idea is to give you good throttle response, and provide the power you're demanding. Also to prevent an overly lean mixture from hurting your motor. So it should happen without a lag, I think.

I have been tried P&G (neutral, not EOC) and it looks promising.

I think coasting in neutral is a very powerful technique. I think it's easy to underestimate the drag created by coasting in gear, and I think this drag probably overwhelms the benefit of DFCO.

EOC is great, but it requires very specific driving conditions.

[theholycow]

Originally Posted by dosco

Fair enough, but the next logical question: what device out there actually measures fuel flow in passenger cars?

That's under heavy discussion in the "realtime monitoring tools for pre-OBD cars" thread.

Originally Posted by monroe74

Sorry, I know I'm a major offender in this regard. I should realize it's probably annoying. I'm just so used to doing it the old-fashioned way, but I'll give it a try.

Thanks, it's much easier for me (and I hope everyone else) to follow.

I think one of the interesting things about open-loop is that it's something my car generally doesn't do, as far as I can tell. I think a characteristic of wideband-sensor systems is that open loop occurs only when the engine is cold, or when there's some kind of a sensor failure.

Why wouldn't it happen when you go WOT at high RPM?

With my DMM, I can monitor my O2 sensor directly, and the response is immediate. That is, I can see AFR changing right away, as I move the throttle.

So, if I tap a wideband O2 into my exhaust, I can hook it up to a DMM and have a realtime AFR gauge? I don't think I'd risk it in my leased VW but I'll do it in the vehicles I own.

But you're reading info indirectly, with Vag-Com getting the data from your car's computer in OBD format (I think that's how it's working; I could be wrong). That's a more complicated process, so it's harder to tell where the delay is being introduced.

It might be using OBD, or it might be using VW's proprietary protocol, I'm not sure which one it's using. You're right, with these systems being effectively black boxes to me, I can't tell where the delay is.

I think coasting in neutral is a very powerful technique. I think it's easy to underestimate the drag created by coasting in gear, and I think this drag probably overwhelms the benefit of DFCO.

Well said! It never seemed like much drag, but in neutral it becomes obvious that it was. Now I use DFCO when I'm planning on slowing anyway, and neutral when I coast. The fuel cost to idle is less than the momentum lost using DFCO.

EOC is great, but it requires very specific driving conditions.

My commute has a few places perfect for it. I tried it once and got three angry beeps from my car, now I'm afraid of how it could bite me in the *** in the event of a warranty claim, so I won't do it again until I can find out what the three beeps meant. Unfortunately, when I asked on a VW forum, all I got was moral judgement and hate; they were more interested in why I did that than why it beeped. There's another bigger forum where I'm not a member, but I might join to ask.

[Dalez0r]

As for the leanburn vs P&G argument...


To me, the answer seems simple. Leanburn is obviously there to compensate for poor engine efficiency at light throttle by leaning the engine, which reduces power, which requires you to give it a bit more throttle to maintain power... which reduces pumping losses in addition to being a slightly more efficient burn. But, it also seems obvious that the engine produces more output energy per lb of fuel at high load (low rpm obviously)

So, the answer is to use them according to driving conditions. If you can P&G, DO IT! If you're not in a position to do so, you may need to DWL for a while, and leanburn is better for that than non-leanburn.

[dkjones96]

Honestly, thermal efficiency is by far the biggest player in all of this.

At part throttle there isn't much air in the chamber. That small amount of air doesn't have a lot of heat in it when you ignite it so more of the heat goes to the cylinder walls instead of pushing the piston back down, it burns slower because it isn't as dense making for timing advances that rob the engine of efficiency and at part throttle it's working against a vacuum, a partial parasitic loss only if there is enough vacuum in the chamber left to pull the piston up on the bottom portion of the compression stroke.

At WOT you have way more air in the chamber. The larger amount of air has much more heat that would have to be absorbed into the engine, it does get absorbed but the ratio of heat created to amount absorbed plummets as engine speed and throttle increases. Since there is more heat in the chamber the pressure stays higher longer and can actually perform work. The air is very dense when you get close to the top of the compression stroke and results in a faster, better burn requiring less timing advance and increasing efficiency. At WOT you have MUCH less loss from pumping on the intake stroke but you end up with more losses on the compression stroke as has been mentioned, however, when you are compressing the gases you are building potential for the event happening in the power stroke. Not just throwing it away.

[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