\Back fire\
(a) A fire started ahead of a forest or prairie fire to burn
    only against the wind, so that when the two fires meet
    both must go out for lack of fuel.
(b) A premature explosion in the cylinder of a gas or oil
    engine during the exhaust or the compression stroke,
    tending to drive the piston in a direction reverse to
    that in which it should travel; also, an explosion in the
    exhaust passages of such ah engine.

\Back"-fire`\, v. i.
1. (Engin.) To have or experience a back fire or back fires;
   -- said of an internal-combustion engine.

2. Of a Bunsen or similar air-fed burner, to light so that
   the flame proceeds from the internal gas jet instead of
   from the external jet of mixed gas and air. --
   {Back"-fir`ing}, n.