December 15th, 2010

Backfire at the disco

There is something so appealing about fire but know one can really nail why it is so cool. Is it the heat? The flickering of flames? The noise? If there is one thing that is cooler than fire it is fire being belched out of the arse pipe of a car. As they are so cool, we thought we would tell you how those big arse flames are produced.

The process of a car spitting flames is technically called a backfire. A back fire is an explosion produced by a running internal combustion engine that occurs in the exhaust system rather than inside the combustion chamber.

The term backfire was derived from experiences with early unreliable firearms or ammunition, in which the explosive force was directed out the breech instead of the muzzle.From this came the use of the word “backfire” as a verb to indicate something that produces an unintended, unexpected, and undesired result; i.e when you tell an appalling joke and no one laughs.

A car backfire is generally down to a malfunction related to the air to fuel ratio. Backfiring can occur in carbureted engines that are running lean where the air-fuel mixture has insufficient fuel and whenever the timing is too advanced. As the engine runs leaner or if there is less time for the fuel to burn in the combustion chamber, there is a tendency for incomplete combustion. Another backfire situation occurs when the engine is running rich (with excess fuel) and there is incomplete combustion during the cycle.

Exhaust system backfires occur in engines that have an emission system malfunction, like an air injection system diverter valve problem, an exhaust leak, or when the catalytic converter has been removed. In some high-performance vehicles, when a driver shifts up and lets off the accelerator, the engine has a moment of running rich. This causes an incomplete burn which causes the fumes to explode in the exhaust system along with an audible clacking sound. However this condition is a result of working smog equipment, and is unlikely to cause any damage.

So there you go, that is your science lesson for the day. There is a lot going on to make those awesome flames that spit out of the rear of cars. Now you can go and show off to your mates down the pub.

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