[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.

Originally Posted by kubark42

it seems that that is the accuracy that people on this forum are getting.

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?

Originally Posted by kubark42

Furthermore, Luxembourg is home to Delphi’s fuel injection research center (although they might have others). I spoke with one of my colleagues who researches direct gasoline injections, and he felt that this level of repeatability sounds reasonable.

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.

Remember, if you can't measure it, it isn't science!

Originally Posted by kubark42

However, this is a trivial problem, as by simply adding a voltage sensor to each injector, instead of only one, the problem is solved.

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.

Originally Posted by kubark42

A bigger problem is what to do with diesels. Most cars sold over here are diesels, and this technique does NOT work for them.

But there are relatively low cost methods that do. For example, wideband UEGO measurement is becoming mroe 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.

Originally Posted by kubark42

Hmm… my initial thought is that the fact that a 17-dimension non-linear observer with asynchronous outputs (data measurements) converges to a correct value is not low-hanging fruit.

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!

If the cause of error is not understood and established, then there is no reason to presume that incrememtal 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.

Originally Posted by kubark42

What is the expected V/P slope, and keeping in mind that we’re looking at total system efficiency, where should we expect to see it?

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.

Originally Posted by kubark42

As to the second, I’m not sure I follow. Are you asking if fuel consumption data is “connected to either fuel consumption or emissions?” I think I might be missing the scope of your question.

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).

If you are piloting an big car, it is another story. Like the plane, your peak performance is improved, but you aren't using peak performance, you are driving the same speed as always. How do you do this? You throttle back.

What does a throttle create behind it? Vacuum. So the VE of the engine is lower. That is, to obey the rules of the road, the engine is operated farther from peak efficiency...

And this is just the tip of the iceberg. The point of all this is that I doubt that a typical user here would be able to, say, save any fuel using your efficiency measurement, because your model simplifications mean that you inherently are least accurate in the parts of the opeartional envelope where they have no choice but to operate.

I also doubt that it is much use on the vehicle development side. If you make a criteria that a car only has to drive on surface streets, you can make it more fuel effient because you can put a smaller engine operating at higher effiency at relatively low speeds. Once the vehicle goes on a highway, you have to carry more weight to protect the occupants, and you need a bigger engine to propel the increased mass at higher speeds. Inherently, when that vehicle is operated at lower speeds, you will, by nec. be farther from the efficiency island of the engine.

The directions we have been going are smaller, turbo charged, higher compression engines, and you are not really compatible with those fuel delivery technologies - and making certain forms of very ineffient operation more efficient, and you are, again, least accurate in these parts of the operational envelope with your measurements and calcuations.

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

Good Luck
-jjf

P.S. I mean it, I short changed a lot of important subjects above, but I didn't want to let it sit for days, since your paper is still relatively fresh in my mind today.