What kind of specific gravity sensor measures any combination of alcohol and gasoline?

Question

It's output must be electrical.

Part of the electrical output will go to a solenoid, that by opening or closing, adjusts the vacuumn advance on a car - which in turn adjusts the timing. The other part of the electrical output will go to a different solenoid, that adjusts the air-fuel ratio in an old fashioned carberator.

The object of this is to turn my 1963 Volkswaqgen Beetle into a fuel flex car, that can run off any combination of acohol or gasoline. The alcohol will come from a moonshine still.

Calibration of the timing and air-fuel ratio mix, will be done by using gasoline as the zero reference point. Since plans on the internet exist for making my car run off PURE ALCOHOL, then the air-fuel ratio and timing for alcohol , will be used as the high end reference point. Mixtures of gasoline and alcohol, as determined by the sensor, will be used to adjust the engine for variations in-between.

Tried automotive section - no takers on this question.

Thanks David in Kenai.

You gave me some valuable advice - especially about the density changing with temperature. As for automation? I can automate it. I didn't learn how to program microprocessors and build microcontrollers for nothing. :)))))

Sorry - no vintage VW parts available.

Answer 1

The problem I'd see with using density is that ethanol (0.789) is so close to gasoline (0.72-0.76 and varies seasonally because vapor pressure specs are different in summer and winter).

That is a dang fine cut to determine in a moving vehicle. Vinters use a hydrometer with a very low neck to make an accurate density determination. But you are left to stablize and digitize that physical device. A regular fuel-tank sender unit would be one way to make an electrical signal, but it expect quite a force from a 50-100cc float, not the very minor force from a hydrometer.

Another approach from the winemakers is a Brix scale device. Uses the difference in refractive index. Here's an electronic one for a grand: http://www.reichertai.com/products.html?productID=20?referrer=google_brix

How about electrical conductivity of the mixture? Low for both, but much lower for gasoline than for alcohol. Then do a straight-line correlation between gasoline and ethanol conductivity. Here's one: http://www.specmeters.com/Conductivity_Meters/Cardy_Twin_EC_Meter.html I've gotten simple ones for $80 or so, but really, you just need one conductor in the fuel and use the tank as your other electrode.

Or dial in the ratio on the dash board. I applaud your efforts to automate it, but if this is YOUR daily driver, you're obviously deeply into it and tracking all the data anyway.

For the air-fuel ratio, the obvious thing would be do feedback trim based on tailpipe O2 levels. If you had a catalytic, I know you aim for 1% O2 in the tailpipe. There were such smart carberators in cars around 1986-1988 just before carberators went away in favor of fuel-injection. Maybe you could pry the circuitry and solenoids (or the whole carberator) off such a car. My 1988 Chevy Nova/Toyota Corolla was set up like that (and, with 315,000 miles on it, someone is still driving it around town.)

Got an extra VW front axle/suspension lying around? I'm converting a Yahama 400 scooter into a high mileage, enclosed 3-wheeler.

Good luck.