"A sharp metallic sound produced in the
internal combustion of engine is known as knocking."It results in a huge loss of energy.
Gasoline or petrol is
used as a fuel in internal combustion of engine. The vapours of petrol mixed
with air are compressed by piston and allowed to burn in the cylinder of engine
after sparking. This produces large expansion resulting in the movement of
piston and consequently the automobile.
But if the petrol is
of such quality that its vapours mixed with air can ignite prior to high
compression on passing of firing spark, the energy produced by burning of fuel
is not utilized in moving the piston, rather. is lost in creating a metallic
sound, called knocking.
"It is infact
maximum in petrol containing straight chain paraffins but is not produced in
branched chain compounds."
The tendency to knock
decreases in the order is straight chain alkanes
> branched chain alkanes > olefins > cycloalkanes aromatic
hydrocarbons.
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