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 claims BIG reductions in fuel consumption.
There's also an issue of pulse-width modulation to reduce injector heating. Sounds like this just reduces average current, but the mechanical parts don't move during this interval. I can deal with sorting that out in software.
What am I missing? Tips to improve accuracy without huge additional complexity appreciated.
Remember, I'm not controlling anything or tuning an engine. All I want to do is say, "turn on your gizmo and show me the fuel flow drops to half," so I can get excited about your innovation.
I don't even own a vehicle new enough to have fuel injection and the test car is not close to me. I'd like to start out pretty close to right.