[RedDevil]

The simple main reason why diesel yields better MPG than gasoline is that it is heavier per liter. You get way more carbon atoms in a gallon of diesel than in gasoline.
If it would compare per weight the difference is still there, but about halved. High compression rate and no pumping losses, as mentioned.

I can see how mixing in Browns gas would increase flame speed in some cases. I cannot see how the stability of the process can be maintained, I suspect the mixture would widen the variety that occurs in the combustion process. If you adjust for the pinging that might occur on some strokes, it may burn slow on others.

My brother in law was working on a small generator project. They could not get the combustion process stable, it kept misbehaving in some conditions despite all the effort they put in it. Variance in the fuel properties was the main cause; the minute amount of biofuel mixed in created havoc for that application, straight mineral was fine - but not guaranteed to be on supply.
Just to show how much engineers have to strive towards stabilizing the combustion process and to point out what should be your main concern when trying to mix in any kind of fuel the engine was not designed for.