Announcing a complete solution to mapping engine efficiency

[kubark42]

Originally Posted by jfitzpat

Sorry, I'm going to be terse and may miss some issues, I'm trying to help a plant get to rich burning LP engines the size of houses within the upcoming emissions compliance today because we're anticipating a lot of rain.

Think about that. 1. They calibrate measured to actual with a fudge factor. This covers a number of variables, including driver behavior. 2. They are measuring their results with fuel fillups. Are you certain that they are filling their stock tank systems at existing gas stations to the level of accuracy you are asserting?

Repeatability is repeatability. I’m not a fluids expert, but I do expect that the gas station pump is accurate to beyond 0.1%. Otherwise, they’re making 0.1% on every liter they sell (after all, they’d be stupid to do anything other than have their pumps be at the absolute limit of the law). So if people see +-0.1% on multiple fuel-ups, that’s a strong indicator that they’re on to something.

Then he probably does not work on the fluid dynamics side. I'd strongly recommend that you read some of the SAE research papers in this area. Or, just try an external, and more precisely controllable, tank feeding the conventional one and measure for yourself.

He does CFD models of gasoline fuel injector asymmetrical dispersion patterns at high pressure. (Good lord, the processing power he’s got to throw at this kind of thing. He’s the kind of guy who asks for a 64-core computer, and then runs a process on it for 2 weeks at a time.) But this is besides the point. I’ll explain why just after.

No. Look at the trend in efficiency over the last 3 decades. A big key is higher compression. This means that peak fuel delivery has to high, which makes operating injectors fast enough at idle speeds difficult. There are several technologies in use, but look at peak-hold injectors, which are expressly meant to address this problem.

Now look at modern control methods of peak-hold injectors, which include techniques like PWM. In PWM control, open and close times are conditionally varied - that is, they cannot be simply averaged out, they need to be measured and modeled continuously. This makes for a considerably more demanding measurement system and computations. More sophisticated device, multipled by every injector... It seems contrary to your basic assertion. Add the current trend for muliple injectors and even duel fuels, and it sees dead end.

By measuring current, instead of voltage, we can do the same on peak-hold as we do on saturation injectors. This complicates the sensor package a tiny bit, as now hall sensors or current shunts have to be used instead of simple voltage probes, but does not radically change the problem, nor the solution.

But again, this is getting lost in the details. The internal management system has far better ways of calculating fuel flow than I do. Our method demonstrates that with a certain number of inputs you can reconstruct the efficiency of the system. Whether or not this particular sensoring approach works in the future is not important. In the future we will have newer, better ways. You list one below.

But there are relatively low cost methods that do. For example, wideband UEGO measurement is becoming more common in modern vehicles. If you combine good lambda measurement with, say, MAF, you have volume of air and combustion ratio, so you know the volume of fuel burned.

No! That’s not measuring, that’s inferring. And if you’re not using a model based stochastic filter to do the inferring, you’re not getting the most out your data. Pick your poison-- EKF, UKF, sliding point observers, particle filters, information filters, etc…-- but definitely don’t go without.

In an abstract sense, the UEGO/MAF approach and the injector patency approach are identical, only the physical parameters change. My goal is to observe power_in, and both are valid approaches.

Even better, by the sound of it they are complimentary approaches.That is a perfect proof to my above point that “we’ll find a better way”. So this sounds like a promising line of attack for better models, and more importantly for diesels. Do you have a good reference?

Then you may be thinking about the wrong end of the problem. Look at your simplified model and consider the influence of torque. Now look at your instrumentation, it is all, generally speaking, at best accuracy at peak torque.

Now look at the torque curve and the weighting of your data predictor. You have the least error in your sample prediction and your calculation at peak torque.

On the flip side, forget the physics, math, and sensing and look at the data! Ultimately, you have to explain why your chart has the lowest error, essentially zero, at peak torque, but huge amounts of error elsewhere!

I can’t explain that, in part because I don’t believe that. My observations show a peak of 35% holistic system efficiency. That’s too big, by a heftier margin than I’m comfortable with. But I’m expecting that that is in part because I’m using manufacturer’s data for things such as air resistance and am overestimating tire rolling resistance by a substantial margin (by >25% according to what I saw today.)

Could you specify what it is exactly that is bothering you? For the life of me I can’t see the problem you describe.

If the cause of error is not understood and established, then there is no reason to presume that incremental improvement can occur. In other words, we can't assume it is a matter of better math. It could easily be the precision and limits of your underlying measurements, or even a flaw in your foundational models and premises. In science, everything is on the table until the data is explained and the results replicated.

That is a question of philosophy. Anyone who’s ever studied observers knows that EKF (Extended Kalman Filters for everyone else out there) cannot be shown to globally converge. There is no mathematical proof for it. Yet, in no physical case have they ever been show not to globally converge. So even at the upper echelons of the mathematical world, there is cutting edge research being done, based on something that can’t be proven in a global sense. Even mathematicians are willing to fudge on things and not explain details that aren’t important when the system “just works”.

Now, I’m not saying that this is an excuse nor a reason for every Tom, Dick, and Harry who’s too lazy to cross his t’s, dot his i’s, and expects his new-fangled system to run on imaginium, but I do think it’s a mistake not to go further in this case because we have some nagging unknowns.

Actually, you are not looking at total system efficiency, you are looking at a fairly narrow area of system efficiency, post drive train (but while ignoring many real world events)

As far as the V/P curve and slope, that is too big a question to properly answer here. I'd recommend starting with basic texts in engine design. But, in super brief, think of a single cyl in an engine. Mechancially, we have a constantly changing volume (pistone up, piston down). In combustion, we are creating additional pressure which also follows a curve (picture the flame front radiating from the ignition source while generating an envelope of gases).

If we could somehow create a perfect engine, plotting these two on a two axis graph, we would basically have a repeating rectangle. But chemistry and simle mechanics do not allow this, so we get a deflated and slighly twisted football (American). We do different things to try to draw portions closer to an ideal rectangle, like turbulence in the mix giving faster burns at higher RPMs, but, ultimately, the optimum point of peak pressure to occur is fixed, literally built into the cyl. So all engines have a fairly small peak efficiency island.

Ah, I see. You’re talking about the volume vs. pressure thermodynamic graphs. (Personally, I always preferred entropy vs. temperature, but I guess that just depends on who and what you work with.) Now that I know what you’re talking about in thermodynamic terms, I’m doubly unclear about why I should see the curve, nor which part of it I should expect to see in an efficiency map, esp. a curve-fitted one.

No, I'm saying that your model appears to be too simple to be of much use in actually predicting operational economy. Consider a seemingly simple question, why do people here hate driving in winter?

Simple, fuel economy is worse. But why?

There are actually multiple reasons, even the fuel composition is different, but let's look at just two, emissions and aircharge.

The effiency of a cat is very narrow, both in terms of gas composition and in terms of required exhaust temp. So a modern automobile runs, as much as possible, at lambda 1.0 (actually, the vehicles are closed loop to equivelency ratio, but we often talk about the reciprocal, lambda). This gives both peak EGT, and a cat friendly gas composition.

Now, it is winter, and the air charge entering the engine is denser, so it takes more fuel to reach the same stoichiometric ratio. Simply by virtue of air being dense, you have to burn more fuel at even the lightest loads to keep emissions systems operating.

If you are a small plane pilot, you love cooler denser air, because you are taking off and generally climbing at wide open throttle. That denser air means you climb faster (for multiple reasons, some more important than others, but a big one is the plane is probably normally aspirated and the density altitude is lower).

I am a small plane pilot, and I do love cold days, and cold, clear nights even better. (Just so long as there’s no ice accumulation due to radiative heat loss). But you comparison is unfair. You’re assuming that we claim that the summer efficiency map is the same as the winter efficiency map. Not so.

While we don’t even have enough data yet to show how the holistic efficiency map changes across the seasons (hurry up and get here, summer!), it’s a reasonable guess that it will only change the magnitudes of the efficiency curve, and not its general shape.

I'd be very happy to proved wrong, but you will need to do some experimentation and collect some data to do so!

Well, look at it this way. We have three possibilities:

1) Drivers follow the optimum trajectory through R_17 space and see a net fuel economy increase.
2) Drivers follow the optimum trajectory through R_17 space and see a net fuel economy decrease.
3) Drivers follow the optimum trajectory through R_17 space and see no net change in fuel economy.

Many experiments with manufacturer provided data have shown that #1 is the outcome. See for example the excellent results from E. Hellstrom in “Look-ahead control for heavy trucks to minimize trip time and fuel consumption”. The only question left is, then, “Can we provide a similar increase in system performance with an efficiency map observed from real-world driving?”

Dollars to donuts gets you that the answer is “yes”.

Note that the typical user will NOT be able to guess the optimal control trajectory. If there’s one thing I’ve learned about optimal control as a mechanical engineer, it’s to shut up when the math speaks. Optimal control defies all physical intuition, and it’s terribly frustrating because it is optimal. There is no room for debate with optimal results, there is only room for debate with the model compromises that led to that result. The scary thing is how terribly “wrong” most of what we do is. Well, not wrong, but sub-optimal.

***

Exercise for the reader: you are the driver of a car on a road that is horizontally straight, but that has exactly the shape of a sine curve in the vertical dimension. (Imagine a roller coaster) The car starts of on the righthand side of one of the waves, pointing uphill. You have one single gear, and an ideal clutch (i.e., a clutch that instantly engages without slipping). Your engine efficiency curve looks like a bell curve (i.e. there’s a certain speed toward the middle of the curve at which you have maximum efficiency). Whenever you disengage the clutch, the engine turns off. You have no air or rolling losses whatsoever. (In fact, no losses at all aside from those dictated by the efficiency curve.)

Your goal is to get to the top of the hill three hills to the right, all while using the least energy possible. What is your optimal strategy?

I’ll send a free logging board and an AVRDragon to the first person who gets it right before next week Friday.

[RobertSmalls]

The correct approach is to engage the clutch until you have just enough kinetic energy to crest the first hill, then disengage the clutch and coast the rest of the way. Also, disengage the clutch if engine speed exceeds the peak of the efficiency curve, and re-engage if that is necessary to climb the first hill. The result will be that once the vehicle gets up to the speed corresponding to peak efficiency, it will hold that speed by running the engine at whatever duty cycle is required (this is familiar to ecomodders as pulse and glide).

Vehicle speed at the crest of each hill will approach zero, and the driver will die of old age before he finishes the course.

[jfitzpat]

Originally Posted by kubark42

Repeatability is repeatability. I’m not a fluids expert, but I do expect that the gas station pump is accurate to beyond 0.1%. Otherwise, they’re making 0.1% on every liter they sell (after all, they’d be stupid to do anything other than have their pumps be at the absolute limit of the law). So if people see +-0.1% on multiple fuel-ups, that’s a strong indicator that they’re on to something.

I could write a long post about this paragraph alone, but you do see the problem, repeatability, you just missed the application. People here are testing their accuracy against *fillups*. We do not see inside our tanks, so we are relying on a pressure system to kick off before we pour gasoline on the ground.

Do you really think that point is being hit with a high degree of precision?

However, you are actually wrong even in your disbelief. A 15 degF change in fuel temperature makes about a 1% difference in volume with gasoline. The fuel at a station is generally stored in an underground tank, so it's temp doesn't change all that much, but the fuel lines between the tank and the nozzle do. When consumer reports tested morning fillups vs. afternoon fillups, they saw about a .1% change in fuel economy. Edmunds found higher, but over a hotter period of days.

That, by the way, is a clue for one of the reasons that I find your flow accuracy claim dubious when matched to other literature.

Originally Posted by kubark42

By measuring current, instead of voltage, we can do the same on peak-hold as we do on saturation injectors.

Not if they are under modern PWM control. I wish I had a graphic of a typical schematic handy, it would be interesting just where you expect to put your current measurment.

Originally Posted by kubark42

I am a small plane pilot, and I do love cold days, and cold, clear nights even better. (Just so long as there’s no ice accumulation due to radiative heat loss). But you comparison is unfair. You’re assuming that we claim that the summer efficiency map is the same as the winter efficiency map. Not so.

I think that this one paragraph is a perfect metaphore for ths conversation. There is no assumption in my comment on what you can and cannot measure in winter. There is only a verifiable example to back up my point - that there is a difference between engine efficiency and operational efficiency, and the difference varies depending upon application.

The only assumption that I am making is that you are young, and you are trying too hard.

I am old, so I have little patience for this sort of game. Look at your comments about flying. Private Pilot or not, you are still trying too hard to impress.

As it happens, I am also a pilot (ATP rated and CFI/CFII ticket), there are two essential ingredients for icing with a small aircraft, visible moisture and below freezing temperatures. The temps do not have to be around the plane, water droplets can get supercooled high in a thunderstorm and fall on you. But both elements have to be present (it's actually a question in both the private and instrument written test question blocks)

The suggestion that you can be out in clear, below freezing air and experience a dangerous accumulation of icing in flight is patently false. Cold clear air contains very little moisture and sublimation cannot occur under a boundary layer of 100 kt air.

NOTE for any lurking pilots, this does not mean you should ignore frost in your preflight, accumulated frost can have a fairly significant impact on lift. No, you almost certaintly wouldn't fall from the sky, but you may find your deptarture shorter on runway or a lot closer to obstacles than you wish to be - so take a few minutes and properly deice it. AOPA's Air Safety Foundation has a good online course on this.

Now, aside from establishing that you don't seem to know what the FAA would like you to know about icing, what has this accomplished? Nothing.

Likewise, what possible reason could I care about the job title of a nameless person that annecotally supports a claim? Does that meaningfully compete against accurate measurement? If so, then what does it mean that I am (truthfully) part of the team that was recently awarded the SAE/MIT Best Innovate award for green/efficiency automotive technology? Does that suddenly make your friend wrong, or do we have to go into a runoff where we measure lab coat stains or count pens in our pocket protectors?

All this sort of noise does is distract from meaningful dialog. Aside from the surprisingly fierce battle between annecdotal opinion and the existing published literature on precisely measured performance of fuel systems, I'm really making only two very simple, (and I would think) easily understood points.

1. If you print your figure 6 and figure 7 on transparency in matching scales and lay one on the other, redish color on one will fall on blueish on the other.

2. It is not really practical to maximize operation of a car at the center of the red zone - since it essentially identifies peak torque.

That's it, take it, leave it, deny it, circular file it, whatever...

I sincerely hope you continue with your studies, but if you are this fierce about annecdote vs. prior art, research is going to be a very stressful field for you!

Good Luck
-jjf

[jfitzpat]

Originally Posted by RobertSmalls

(this is familiar to ecomodders as pulse and glide).

Very well explained.

Originally Posted by RobertSmalls

Vehicle speed at the crest of each hill will approach zero, and the driver will die of old age before he finishes the course.

I needed that. It is hard for me to not write as a grumpy old man.

Thx

[kubark42]

Originally Posted by RobertSmalls

The correct approach is to engage the clutch until you have just enough kinetic energy to crest the first hill, then disengage the clutch and coast the rest of the way. Also, disengage the clutch if engine speed exceeds the peak of the efficiency curve, and re-engage if that is necessary to climb the first hill. The result will be that once the vehicle gets up to the speed corresponding to peak efficiency, it will hold that speed by running the engine at whatever duty cycle is required (this is familiar to ecomodders as pulse and glide).

Vehicle speed at the crest of each hill will approach zero, and the driver will die of old age before he finishes the course.

In the interests of discussion, I can't comment yes or no until the week is up.

[kubark42]

Originally Posted by jfitzpat

I could write a long post about this paragraph alone, but you do see the problem, repeatability, you just missed the application. People here are testing their accuracy against *fillups*. We do not see inside our tanks, so we are relying on a pressure system to kick off before we pour gasoline on the ground.

Do you really think that point is being hit with a high degree of precision?

However, you are actually wrong even in your disbelief. A 15 degF change in fuel temperature makes about a 1% difference in volume with gasoline. The fuel at a station is generally stored in an underground tank, so it's temp doesn't change all that much, but the fuel lines between the tank and the nozzle do. When consumer reports tested morning fillups vs. afternoon fillups, they saw about a .1% change in fuel economy. Edmunds found higher, but over a hotter period of days.

That, by the way, is a clue for one of the reasons that I find your flow accuracy claim dubious when matched to other literature.

Again, repeatability is repeatability. We cannot comment on how members who report their fuel economy do their fill ups. It is as reasonable to suppose that they stop the first time the handle kick off as they they fill until they see the gasoline reach the filler inlet. As long as people accept 1 part-per-thousand, that’s what I’ll use. And when they no longer do, I’ll change it. You tell me about “the literature”, but for heaven’s sake, my good fellow, give me a specific citation! If the citation says +-1%, I will put that in the study instead, it makes no difference to me.

But we’re getting lost in the details. Let the experts figure out the best way to measure fuel flow, the truly interesting problems for us are in the overall structure.

Not if they are under modern PWM control. I wish I had a graphic of a typical schematic handy, it would be interesting just where you expect to put your current measurement.

I don’t know, but I’m sure someone out there will figure it out and then I’ll have my answer. As problems go, there are far bigger fish to fry than this one. What about electric cars? What about hybrids?

If there’s a modeling or measuring problem, I’m certain we can overcome that when we get to it. The whole reason I’m seeking help on ecomodders is because I only have one car, so I can’t possibly test all the various possibilities.

The only assumption that I am making is that you are young, and you are trying too hard.

I am old, so I have little patience for this sort of game.

This analogy works both ways. The world is as full of stories of old men who claimed it couldn’t be done as of young men who failed trying it.

As it happens, I am also a pilot (ATP rated and CFI/CFII ticket), …

Now, aside from establishing that you don't seem to know what the FAA would like you to know about icing, what has this accomplished? Nothing.

Woah, slow down pardner! You’re dangerously close to the line of “assume makes an ass…” The only thing I’m saying is that I don’t like having to miss my weather window because of ice accumulation (specifically frost, but laymen reading this conversation won’t appreciate the difference as it pertains to aircraft) due to radiative heat losses on clear nights as the airplane is sitting on the tarmac. I also don’t like when condensation on control cables ices up. Kind of gets your sphincter in a tight knot when you’re at 11,000’ and you realize you don’t have ailerons anymore.

(That being said, to all those reading this, what jfitzpat said is correct down to the letter. But in the interests of scientific conversation it is not exactly relevant to the topic at hand, and I kind of wish we could delete this whole aeronautic detour through the woods. Clouds. Whatever.)

Likewise, what possible reason could I care about the job title of a nameless person that annecotally supports a claim? Does that meaningfully compete against accurate measurement? If so, then what does it mean that I am (truthfully) part of the team that was recently awarded the SAE/MIT Best Innovate award for green/efficiency automotive technology? Does that suddenly make your friend wrong, or do we have to go into a runoff where we measure lab coat stains or count pens in our pocket protectors?

All this sort of noise does is distract from meaningful dialog. Aside from the surprisingly fierce battle between anecdotal opinion and the existing published literature on precisely measured performance of fuel systems, I'm really making only two very simple, (and I would think) easily understood points.

1. If you print your figure 6 and figure 7 on transparency in matching scales and lay one on the other, redish color on one will fall on blueish on the other.

2. It is not really practical to maximize operation of a car at the center of the red zone - since it essentially identifies peak torque.

That's it, take it, leave it, deny it, circular file it, whatever...

First, look at it from my perspective. You are a voice on the internet. You could be a crank, or a genius. I have no way of telling. I can only judge based on data. Until you support your arguments with data and/or references, I’m stuck. It is entirely within the realm of reason that you are correct, but you’re asking me to take that on faith over what a fuel injector engineer tells me. A nebulous voice on the internet over the professional down the hall. What would you do?

But the problem is that all this is missing the point. If the error is higher, that’s fine, I just have to detune the observer a tad bit. It doesn’t really change whether I can show gains through optimal control.

Second, getting on to optimal control, who ever said that we would be driving in the area of maximum operation? That’s a big… assumption. Honestly, I can’t tell you what the optimal trajectory for your car will be. I’ve said it before, and I’ll say it again: intuition fails when it comes to optimal control. Your intuition, that you’ve gained after so many years, is standing in your way. It’s an obstruction to you seeing the overall picture.

You seem to know what you’re talking about, but I think you could contribute far more to the conversation if you responded to my questions about sources and references. I would love nothing more than to incorporate your experience into my observer and make for a better model. But what I’m getting out of you is that “I’m trying to hard to impress” and “research is going to be a stressful field”. You seem like a valuable resource, but not like this. A change of direction is in order.

Because the fact is, right now I’m engaging in a dialogue that I don’t have time for either, and that isn’t helping me. My whole theory, rather debate, with my colleagues is that it is far more interesting to engage the internet and get the experience of people who don’t necessarily read journal articles, than to go to conferences, publish in unread reviews, etc… I argue that there is a whole world of untapped cross-disciplinary experience, but we have to go to it instead of sitting on our duffs and expecting it to come to us. Right now I’m losing the battle, severely.

[RobertSmalls]

Mr. Fitzpatrick,

I take it from your posts here and in the "reliable PCB" thread that your specific field of expertise is Antagonism Engineering. Consider also the fact that you are a self-described grumpy old man. Your posts have been longer than necessary, drifting off-topic, and full of sublte personal insults and irrelevant questioning of the qualifications of our guest experts.

Please change. You appear to have considerable technical knowledge and experience. Can you apply it primarily to improving EcoModder projects, instead of simply pointing out their shortcomings?

[tasdrouille]

Originally Posted by kubark42

***

Exercise for the reader: you are the driver of a car on a road that is horizontally straight, but that has exactly the shape of a sine curve in the vertical dimension. (Imagine a roller coaster) The car starts of on the righthand side of one of the waves, pointing uphill. You have one single gear, and an ideal clutch. Your engine efficiency curve looks like a bell curve (i.e. there’s a certain speed toward the middle of the curve at which you have maximum efficiency). Whenever you disengage the clutch, the engine turns off. You have no air or rolling losses whatsoever. (In fact, no losses at all aside from those dictated by the efficiency curve.)

Your goal is to get to the top of the hill three hills to the right, all while using the least energy possible. What is your optimal strategy?

All you have to do is to generate the energy needed to get to the top of the first hill in the most efficient way possible.

Engage the clutch, start the engine, set engine speed (and load obviously) at max efficiency while climbing till you have just enough kinetic energy to make it over the top of the hill at which point you disengage the clutch while you're still climbing, shutting the engine off automatically, you'll just barely make it over the top and you then coast this way going up and down hill for a while with the engine off and just brake (or barely engage the clutch, the resistance of the engine should stop the car) when you want to stop at the very top of the third hill.

[dcb]

re Exercise for the reader:

In the real world there are soo many variables that I would probably give a mpguino like program/device an accelerometer (because we are on a changing slope) and throttle control, and maybe a hint that the load would be decreasing and have it seek/adjust the most efficient throttle position, then try to make sense out of it

course I don't know what exactly an "ideal clutch" means.

[tasdrouille]

I believe there is more than a 0.1% error in fill to fill variations. Especially if you fill at different pumps. Although I believe they measure fuel accurately, I do not think they will all stop at the same level. Also, since a fuel tank is an irregular conainer, if your car is tilted in different ways, the error can easilly go past 0.1%.

You should try to do coastdown tests to validate the manufacturers value you input in your model (Cd and Crr). Maybe revalidate the frontal area too. As already suggested, you could validate you fuel measurements from MAF and O2 sensor output.

Also, Crr gets lower as the distance driven increase (as the tire gets hotter, hysteresis losses are reduced). There are a lot of other variables that will change like that depending on the trips you log.