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.
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Zones of Flame:
There are three zones in flame, viz. outer zone, middle zone and inner zone.
This zone is blue in colour. It is the hottest part of the flame, because complete combustion takes place in this zone.
This zone is yellow and orange in colour. This zone is moderately hot because partial combustion takes place in this zone.
This zone is dark in colour. This is the coolest part of the flame because no combustion takes place in this zone.
Characteristics of a Good Fuel:
- It is readily available.
- It is cheap.
- It burns easily in air.
- It burns at a moderate rate.
- It produces a large amount of heat.
- It does not leave behind any undesirable substance.
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|
Harms of Burning of Fuel
- Burning of carbon fuels (wood, coal, petroleum) results in release of unburnt carbon particles in air. These particles cause respiratory disease; like asthma.
- Burning of most fuels releases carbon monoxide. It is a poisonous gas; even at low concentration. Hence, coal should not be burnt in a closed room.
- Burning of most fuels results in release of carbon dioxide in atmosphere. Higher level of carbon dioxide in the atmosphere causes global warming.
- Burning of coal and diesel results in release of sulphur dioxide in air. Burning of petrol produces oxides of nitrogen. Oxides of sulphur and nitrogen mix with rainwater; to cause acid rain. Acid rain is harmful for living beings, buildings, and for monuments.