Flame is the visible and gaseous part of fire. When vapour of a substance undergoes combustion, it results in flame. Only those substances which vaporize on burning produce flame. If a substance does not get vaporized, it does not produce flame.
There are three zones in flame, viz. outer zone, middle zone and inner zone.
Outer Zone: This zone is blue in colour. It is the hottest part of the flame, because complete combustion takes place in this zone.
Middle Zone: This zone is yellow and orange in colour. This zone is moderately hot because partial combustion takes place in this zone.
Inner Zone: This zone is dark in colour. This is the coolest part of the flame because no combustion takes place in this zone.
There is probably no fuel which can be considered as ideal fuel.
Ccalorific value gives the measure of fuel efficiency. The amount of heat energy produced on combustion of 1 kg of a fuel is called calorific value of that fuel. It is expressed as kilo Joule per kg (kJ/kg).
|Calorific values of fuels|
|Fuel||Calorific value (kJ/kg)|
|Cowdung cake||6000 – 8000|
|Wood||17000 – 22000|
|Coal||25000 – 33000|
|Biogas||35000 – 40000|
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