Combustion and Flame

Candle burns with a flame but coal does not burns with a flame also coal is a carbon product and its burning is harmful for environment but candle is made from wax its burning is not as much harmful as burning of coal

The chemical process in which a substance reacts with oxygen to give off heat is called combustion, in combustion the release of heat can result in the production of light in the form of either glowing or a flame.The substance which undergoes combustion is called combustible or fuel. Fuel may be solid, liquid or gas. Example: burning of a coal shows the process of combustion and coal here is combustible or fuel.

Food is a fuel for our body because inside our body food is broken down into simpler form by reaction with oxygen and with the release of heat and energy.

Wood, paper, kerosene oil, charcoal

Take two lighted candle A and B, and place them on a table, now put a transparent glass over candle B and see what happens to the candle B, we will observe that candle flame flickers and produces smoke and finally it goes off, this is because on putting glass over it, the air supply was cut off and candle was unable to burn in the absence of air.

Take two lighted candle A and B, and place them on a table, now put a transparent glass over candle B and see what happens to the candle B, we will observe that candle flame flickers and produces smoke and finally it goes off, this is because on putting glass over it, the air supply was cut off and candle was unable to burn in the absence of air.

To cut off the air supply of the fire, so that the fire gets off and the person could be saved from fire.

A forest fire is a natural disaster consisting of a fire which destroys a forested area, and is dangerous for the people living in forest area as well as for the wildlife, during extreme heat of summer, at some places dry grass catches fire, the fire get spread from grass to tree, and very soon whole forest catches fire.it is very difficult to control such fires.

The lowest temperature at which a substance catches fire or the lowest temperature at which combustion begins and continues in a substance is called its ignition temperature. Match Stick cannot catch fire on its own at room temperature because it can catch fire only at its ignition temperature not at room temperature.

The head of the matchstick is made from antimony trisulphide and potassium chlorate. The rubbing surface has powdered glass and a little red phosphorus. When the matchstick is struck against the rubbing surface, some of the red phosphorus is converted into white phosphorus; this immediately reacts with potassium chlorate in the matchstick head to produce enough heat to ignite antimony trisulphide and starts the combustion of matchstick.

This is because the specific heat capacity of the wood is more than the kerosene oil. So, the wood takes time to burn but burns for longer period than the kerosene oil.

Because kerosene oil can catch fire very easily as its ignition temperature is lower than other combustible material.

Inflammable substances have very low ignition temperature and thus they can easily catch fire with a flame, example: diesel, kerosene oil, alcohol, Liquefied Petroleum Gas (LPG) etc.

As we know there are three essential requirements for producing fire these are fuel, air and heat. Fire can be controlled by removing one or more of these requirements that is either by cutting of the air supply, or by bring down the temperature of the fuel or both.

Fireman through water with pressure on fire, water helps in cooling down of the combustilbe material so that its temperature is brought below its ignition temperature and fire does not get spread. A part from this combustible material is surrounded by water vapour which helps in cutting of the air supply and finally fire is extinguished.

The most commonly used fire extinguisher is water, it works when wood and paper are on fire, but if electrical equipment is on fire water may conduct electricity and may harm those trying to douse the fire, also water is not suitable for fires involving oil and petrol, since water is heavier than oil it sinks below the oil and oil keeps burning on the top. So if electrical equipment and inflammable materials are on fire Carbon dioxide is the best extinguisher. Since it is heavier than oxygen it covers the fire so that the contact between fuel and oxygen is cut off and the fire is controlled, it also bring s down the temperature of the fuel. For this purpose carbon dioxide is stored at high pressure as a liquid in cylinders.

Following are the essential requirements for producing a fire:

1. Fuel: that is the combustible material
2. Air: air supplies oxygen which supports combustion and without which it is impossible to set on a fire.
3. Heat: heat is important as it raises the temperature of the fuel beyond the ignition temperature.

The most commonly used fire extinguisher is water, it works when wood and paper are on fire, but if electrical equipment is on fire water may conduct electricity and may harm those trying to douse the fire, also water is not suitable for fires involving oil and petrol, since water is heavier than oil it sinks below the oil and oil keeps burning on the top. So if electrical equipment and inflammable materials are on fire Carbon dioxide is the best extinguisher. Since it is heavier than oxygen it covers the fire so that the contact between fuel and oxygen is cut off and the fire is controlled, it also bring s down the temperature of the fuel. For this purpose carbon dioxide is stored at high pressure as a liquid in cylinders.

The most commonly used fire extinguisher is water, it works when wood and paper are on fire, but if electrical equipment is on fire water may conduct electricity and may harm those trying to douse the fire, also water is not suitable for fires involving oil and petrol, since water is heavier than oil it sinks below the oil and oil keeps burning on the top. So if electrical equipment and inflammable materials are on fire Carbon dioxide is the best extinguisher. Since it is heavier than oxygen it covers the fire so that the contact between fuel and oxygen is cut off and the fire is controlled, it also bring s down the temperature of the fuel. For this purpose carbon dioxide is stored at high pressure as a liquid in cylinders.

There are three types of combustion:

1. Rapid combustion: Bring a burning matchstick or gas lighter near a gas stove and turn on the knob of gas stove, we will find the gas burns rapidly and produces heat and light, such combustion is called as rapid combustion
2. Spontaneous combustion: In this type of combustion a material suddenly bursts into a flame, without the application of any apparent .e;g spontaneous combustion of coal dust.
3. Explosion: When a cracker is ignited a sudden reaction takes place with the evolution of heat, light and sound, this type of combustion is called Explosion.

A flame is the visible, gaseous part of a fire. The substance which vaporise during burning give flames, It is caused by a highly exothermic reaction taking place in a thin zone.

We will observe a circular blackish ring formed on the glass plate, this indicates the deposition of unburnt carbon particles present in the luminous zone of the flame.

A good fuel is one which is:

• Readily available
• Ignite easily
• Burn well, not with explosion
• Cheap
• Produces a large amount of heat
• Have low smoke and ash content
• Should be easy to store and transport

Calorific value of the fuel is the amount of heat energy produced on complete combustion of 1 kg of fuel; it is expressed in kilojoule per kg.

Calorific value of wood is 17000-22000 kj/kg
Calorific value of coal is 25000-33000 kj/kg
Calorific value of CNG is 50000 kj/kg
Calorific value of biogas is 35000-40000 kj/kg

Increasing fuel consumption has harmful effects on environment because:

• Carbon fuels like wood, coal and petroleum releases unburnt carbon particles that are dangerous pollutants causing diseases like asthma and respiratory disorders
• Incomplete combustion of these fuel releases a very poisonous gas carbon monoxide
• Release of carbon dioxide gas by combustion of fuels is becoming one of the cause of global warming

Global warming is the increase in the average temperature of Earth's atmosphere and oceans, reason for the same is;Increasing population that leads to increased use of fossil fuels and agriculture, fossil fuels releases carbon dioxide gas which causes global warming, because of increased population more number of people releases carbon dioxide gas during respiration process and that contributes to global warming, increased demand of agriculture for our increasing population is also one of the reason of global warming as manures used in agriculture contains methane gas.

Global warming is the increase in the average temperature of Earth's atmosphere and oceans, it results in melting of the glacier of the polar region which leads to rise in sea level, causing flood in coastal areas. Even low lying coastal region may get permanently submerged under water because of global warming.

A heap of green leaves contains lot of water and has very high ignition temperature, as water is a natural fire extinguisher it do not allow leaves to catch fire easily where as dry leaves contains no water and have low ignition temperature thus they can catch fire easily.

Calorific value of the fuel = Amount of heat energy produced / weight of fuel burnt

= 160000/3.5 kj/kg
= 45714.28 kj/kg