What is Combustion?
In simple terms, Combustion is the process of burning. It is a chemical reaction in which the fuel or the substance reacts with an oxidant or oxygen to produce heat. For instance, the burning of petrol or diesel in a vehicle, burning natural gas on the stovetop, burning wood for cooking or in a fireplace, etc can all be considered as combustion.
Combustible Substances
Substances that can burn with the help of oxygen are called combustible substances. Heat and light are given away during the process of combustion. It is also known as fuel. Fuel can be in either a solid, liquid, or gas state.
Inflammable Substances
Substances that catch fire easily or which have low ignition temperature are called inflammable substances.
Non-Combustible Substances
Substances that cannot burn with the help of oxygen are called non-combustible substances.
Combustible substances have a required combustion temperature to burn or catch fire which varies for different substances.
Conditions for Combustion
Combustion has mainly three requirements, namely, fuel, air, and ignition temperature.
Combustion can only take place when there is a fuel or a substance that can catch fire and release heat and light as a result.
The process of combustion will take place only when there is a presence of air. Combustion would not take place when practised in a closed space without air.
Ignition temperature is the temperature at which the fuel catches fire for burning. If the temperature is lower than the ignition temperature of that specific fuel, it will not burn.
Common Examples of Combustion
Some of the common examples of combustion are listed below:
Burning of wood.
Burning of a candle.
Burning of natural gas on the stovetop.
Burning of sulfur.
Explosion of Hydrogen in air.
Types of Combustion
There are mainly three types of combustion.
1. Complete Combustion
Complete combustion is the process in which the fuel is allowed to react with an oxidant with an unlimited supply of air. This ends up in the complete burning of the substance and as a result, a byproduct is also produced. Carbon dioxide and water are produced. For example, when we burn wood using fire, if it is allowed to burn until ashes are produced, it is a complete combustion process.
2. Incomplete Combustion
In incomplete combustion, when the fuel is not provided with adequate oxygen, it will not burn completely. So the by-products of carbon dioxide and water are not produced.
3. Rapid Combustion
Rapid combustion is the type in which the fuel or the substance catch fire rapidly. For instance, when we bring a lighted match stick or candle near a gas stove which is turned on, it will catch fire very quickly. As a result, heat and light are produced.
1. Spontaneous Combustion
In this type of combustion, the substance catches fire abruptly without a known cause and it tends to spread easily too. For example, a forest fire is caused by the rubbing of dried tree trunks or a spark caused by unknown sources that create wild and uncontrollable fire.
2. Explosion Combustion
In this type of combustion, a quick blast of fire, light, heat, and sound is produced. For example, when a cracker is lighted, it blasts with light, sound, fire, and sound. And it releases a high amount of gas as well.
Combustion Fuel
Combustion fuels are the substances that are used to cause fire or to cause combustion. Combustion fuels are in solid, liquid, and gas forms.
Important combustion fuels used worldwide are Petrol, Diesel, coal, oil, LPG, Gasoline, wood, etc. Each of these combustion fuels has its characteristic features when it comes to the reaction. When the quantity of carbon in the fuel is increased, more air is required for the complete combustion of the substance.
Liquid Combustion Fuel
Liquid combustion fuel is combustion in which the fuel is in liquid form. It doesn't have a specific shape but takes the shape of the vessel it contains. Examples of liquid combustion fuels are petrol, diesel, kerosene, etc.
Gaseous Combustion Fuel
Gaseous combustion fuels are combustion fuels which are in gaseous form. For example, LPG. Gaseous combustion fuel is a comparatively more dangerous and uncontrollable form of combustion fuel.
Solid Combustion Fuel
Solid combustion fuel is the combustion in which the fuel is in solid form. Examples of solid combustion fuel are coal, wood, etc.
FAQs on Combustion Fuel
1. What is combustion and what is a fuel?
Combustion is a rapid chemical reaction between a substance and an oxidant, usually oxygen, that produces heat and light. The substance that undergoes combustion is called a fuel. Fuels can exist in solid, liquid, or gaseous states, such as wood (solid), petrol (liquid), or LPG (gas).
2. What are the three essential requirements for combustion to take place?
For combustion to occur, three components, often referred to as the 'fire triangle', must be present:
- Fuel: A combustible substance that can burn.
- Oxygen: An oxidant, typically supplied from the air, to support the reaction.
- Heat: Sufficient heat to raise the fuel to its ignition temperature, which is the minimum temperature required for it to catch fire.
3. What are the main types of combustion explained with examples?
Combustion is primarily classified into three types based on its speed and initiation:
- Rapid Combustion: This occurs very quickly, releasing large amounts of heat and light. An example is the burning of LPG in a gas stove.
- Spontaneous Combustion: This type starts on its own without any external heat source when a substance reaches its ignition temperature due to self-heating. A forest fire starting from the heat of the sun is an example.
- Explosion: This is an extremely fast combustion that happens in a confined area, producing a large volume of gas along with heat, light, and sound. The bursting of a firecracker is a common example of an explosion.
4. What are some common examples of solid, liquid, and gaseous fuels?
Fuels are categorised based on their physical state. Common examples include:
- Solid Fuels: Coal, wood, charcoal, and cow dung cakes.
- Liquid Fuels: Petrol, diesel, and kerosene.
- Gaseous Fuels: Compressed Natural Gas (CNG), Liquefied Petroleum Gas (LPG), and hydrogen gas.
5. What is the difference between complete and incomplete combustion?
The key difference lies in the amount of available oxygen. Complete combustion occurs in a sufficient supply of oxygen and produces carbon dioxide (CO₂), water, heat, and a clean blue flame. In contrast, incomplete combustion happens when oxygen is limited, producing dangerous carbon monoxide (CO) gas, soot (unburnt carbon), and a sooty yellow flame.
6. Why is water effective for extinguishing a wood fire but not an electrical or oil fire?
Water extinguishes a fire by cooling the fuel below its ignition temperature and cutting off the oxygen supply. This works for materials like wood and paper. However, it should not be used for:
- Electrical Fires: Water is a good conductor of electricity and can cause a severe electric shock.
- Oil Fires: Water is denser than oil. It sinks below the burning oil, causing it to splash and spread the fire rapidly. Foam or carbon dioxide extinguishers are used instead.
7. How do the harmful by-products of burning fuels affect the environment?
Burning fuels releases several pollutants with significant environmental impacts:
- Burning coal and diesel releases sulphur dioxide, while petrol engines release oxides of nitrogen. These gases dissolve in rainwater to form acid rain, which damages crops, soil, and buildings.
- Incomplete combustion produces carbon monoxide, a highly toxic gas.
- Most fuels release carbon dioxide, a primary greenhouse gas linked to global warming and climate change.
8. What makes a substance 'inflammable', and how does it relate to ignition temperature?
An inflammable substance is a material that has a very low ignition temperature and can catch fire very easily. The low ignition temperature means that only a small amount of heat is needed to start the combustion process. This is why substances like petrol, alcohol, and LPG are considered highly hazardous and require special safety precautions during storage and handling.
