You don't mix fuel and oxidizer between LEL and UEL except at the burner. If you are smart, you don't mix them at all except at the burner. Remember flashback barriers. Premix burners snap back when flow velocity drops. Carbureted engines became fuel injection - fires, aside from efficiency and raw fuel evaporation emissions.
One of my friends heated alcohol in a test tube over a burner. The alcohol heated preatty fast... then it turned into a flamthrower ... well I better start paying attention ( I am in the middle of enviromental science class)
---------------- psalms 23
The difference between genius and stupidity... genius has its limits.