Those things are interesting gimmicks- - - - - -I'm sure P.T. Barnum would have been selling them a century ago if he had the chance. The problem is that interpreting combustion flame front color is a very subjective thing at best, and there are far too many variables involved to make such things a reliable way of evaluating fuel mixtures. I had a single cylinder "glass engine" in my classroom for several years. The cylinder was made of tempered glass and the piston rings were made of leather to prevent scratching the glass. A plastic shield surrounded the cylinder, and compressed air was blown into the shield to cool the cylinder. With a delay-flash timing light, I could "freeze" the piston at whatever height in the cylinder I wanted and we could watch the color of the flame front as the fuel burned. A very rich mixture had a yellow color, and as the mixture was leaned out the color went from yellow to orange, to light blue, to a deep "Prussian Blue" just before the mixture got too lean to burn. It was an interesting way to teach air/fuel mixtures, but totally impractical as a way to actually tune an engine. We ran that thing on all sorts of fuel- - - -gasoline, alcohol, Propane, lighter fluid, Mineral Spirits, Lacquer thinner, even a mix of gasoline and Diesel. It didn't have enough compression to run on straight Diesel, even with a spark plug trying to light it. I usually ran it on alcohol or Propane- - - - other fuels had a tendency to soot up the cylinder and it was a pan in the posteriori to disassemble it and clean the glass.
Just my opinion- - - - -based on close to 30 years' time using that engine as a teaching aid! Now, pretty soon somebody who's the president of his own fan club will come along and assure everybody I'm spreading a load of fertilizer!
Jerry
