Measure fuel consumption from injector signal?

mike · 2011-07-18T20:07:08+00:00

I need to measure relative fuel consumption. Backstory... I have friends interested in energy efficiency. "Something-for-nothing" transportation is a favorite topic (of theirs). I was asked to go look at a car with a gizmo added to improve fuel efficiency. The guy was all bubbly about his modifications. I asked to see some data. His answer was typical: "I filled her up, drove her 80 miles, filled her up again at a different station. WOW, I got 60MPG." I asked why he didn't use a fuel flow meter. Answer was again typical, "what's a flow meter?" I firmly embrace "conservation of energy", but everything ever invented was impossible before it was invented. I'd like to keep an open mind (and keep my friends happy) that there might be some as-yet undiscovered synergistic effects that improve overall efficiency without violating the basic principles of thermodynamics we know today. Since most claims are bogus, a quick means to debunk them is in order. Adding a fuel flow meter is rather invasive, so I'm looking at ways to measure RELATIVE fuel flow non-invasively. I know nothing about the technology past what I learned in a few hours of googling. In steady state, the rate of fuel flow should be linearly proportional to the open-time of an injector times the number of injection events/unit time. But it's an electromechanical system with short time elements. It takes time for the magnetic field to build/collapse and more time for the mechanical parts to move. In a symmetrical system, this would make the fuel flow time approximately equal to the pulse width, shifted by the delay. I don't understand the terminology, but I'm reading about a 1ms time that needs to be added to the pulse width, on average. I'm leaving out all the complexity of voltage corrections and assuming the fuel pressure regulator is working. If I measure the pulse width and subtract 1ms, will I get a reasonable measure of relative fuel flow? I don't need ultimate precision. Any claim worth debunking...

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mike 15 years ago

Can you give some details on the differences? This whole thread has been about that issue. But no specifics have been disclosed.

I think that might be likely, but I'm still interested in the error terms and being all I can be.

That's what I'm counting on. But if I'm gonna write some code, it seems prudent to be as accurate as I know how.

You're being more generous that I am. 57MPG average repeatable sustained is preposterous for a 94 Honda with a stock 34MPG...no, I don't know which model, but I do know it wasn't an Insight.

I'm gonna clip a current transformer on the wire to an injector.

I agree, in theory. Practice is somewhat different. At 57MPG it takes a lot of miles to rack up enough consumption to accurately determine by reading the pump when you fill up.

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ben91932 15 years ago

Wow... that was harsh. I used to belong to several mpg groups, but gave up on them as most of the guys were pie-in-the-sky free energy guys. They had either put 2 ounces of acetone in the gas or a magnet on the fuel line and claimed wild results. A few guys had good results with aero mods on Metro's and claimed 55 -

60 mpg which passed the sniff test. I am ever leery of someone who has a new product that they 'arent allowed' to talk about, as they mostly seem to be tin foil hat types who use those silly hydrogen generators or the tornado intake swirleygig or a top secret 100 mpg carburetor that the oil companies would kill for... Good luck with your project.. it would be cool if you pull it off. The only way I have ever had any luck with repeatable mpg measurements was on a dyno with super accurate throttle instrumentation and small fuel runs.

Ben

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AMuzi 15 years ago

-snip-

perhaps measuring actual fuel flow might be one approach:

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removing injector variables, unless it's a looped rail system.

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hls 15 years ago

For what he wants, this is all a waste of time and money. Seriously, essentially all of this mileage improvement crap is just a scam. If he wants a REAL answer, take the car and put it on a dynomometer. Dont fart around with cheap fixes that will tell you nothing.

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Steve W. 15 years ago

That's the problem The OP wants cheap and easy. Neither of which will work on the vehicle in question. Total lack of understanding of the actual systems involved and the "I can't discuss much about it" BS.

Is it possible to design and build a car that gets very high mileage (say 50-75 mpg.) Yes. However it will be a vehicle like a Smart with very limited abilities and not something that is real practical outside of a large metropolitan area. Basically an enclosed moped.

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mike 15 years ago

Don't forget the total lack of help from the newsgroup in understanding the actual systems involved.

I talked to a woman at a garage sale today. She was driving a Smart Car. She said she gets 38MPG.

I wouldn't mind driving a smart car type vehicle, but I'd expect better gas mileage for my trouble.

At 38MPG, Why bother.

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Steve W. 15 years ago

I have tried them out and wouldn't drive one unless I absolutely had no choice.

Being a FF/EMT who carries a full gear bag, Med Kit, and some rescue gear in the vehicle at all times. Plus using it to tow the various trailers and the "fabulous" roads I usually drive on, I figure a Smart would probably last about a week. Just not a practical vehicle for my wife or myself.

What I would love to see would be a vehicle like an S-Blazer/Trailblazer sized rig with a diesel in it. I have driven a couple of the Jeep Liberties with the CRD engine. They were OK but I'm not real fond of the vehicle as a whole.

With some of the calls I have been on it would be great to have a vehicle that could set there idling for 3-4 hours without sucking my wallet dry!

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