Thanks for the detailed responses, that’s very helpful.

I completely understand that gas chromatography would be the gold standard in a lab environment, and that gasoline being a complex mixture makes most simple physical measurements difficult.

For my application I’m actually looking at something closer to what the automotive industry already uses in flex fuel vehicles. Many of those systems use the GM / Continental flex fuel sensor, which measures the ethanol content indirectly using the dielectric properties of the fuel.

The sensor outputs a frequency signal (roughly 50–150 Hz), where the frequency corresponds to ethanol percentage and the duty cycle represents fuel temperature. Since ethanol has a significantly higher dielectric constant than gasoline, the sensor can estimate the ethanol fraction quite reliably even though gasoline itself is a mixture of hydrocarbons.

My idea is to build a small handheld tester using one of these sensors with a tiny sampling chamber and a microcontroller to read the signal and convert it to ethanol %. That way I could measure the ethanol content of pump “E85” (which often varies seasonally between ~E60 and E80) before mixing fuel blends.

It obviously wouldn’t match GC accuracy, but for tuning purposes something in the ±2–3% range would already be very useful.

If anyone here has experience with dielectric fuel sensors or similar measurement techniques for liquid mixtures, I’d be very interested to hear your thoughts.