back·fire /-ˌfaɪr/
  逆火,回火,放火(vi.)放逆火,預先放火,發生意外
  backfire, back fire.
  1. 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.
  2.  (a) 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 called a knock or ping. (b) an explosion in the exhaust passages of an internal combustion engine.
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  Back·fire 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.
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  backfire
       n 1: a loud noise made by the explosion of fuel in the manifold
            or exhaust of an internal combustion engine
       2: a miscalculation that recoils on its maker [syn: boomerang]
       v 1: have an unexpected and undesired effect; "Your comments may
            backfire and cause you a lot of trouble" [syn: backlash]
       2: emit a loud noise as a result of undergoing a backfire; "My
          old car backfires all the time"
       3: set a controlled fire to halt an advancing forest to prairie
          fire