In reality, combustion is the consequence of dynamic or time-dependent processes that take place on a molecular level between atoms, molecules, radicals, and solid barriers. Combustion is a chemical reaction that occurs between Fuel (Hydrocarbon) and Oxygen. When fuel and oxygen react, heat and light energy are released. The flame is formed as a result of heat and light energy. As a result, the Combustion reaction formula is Hydrocarbon + Oxygen = Heat energy. Combustion is utilized in automobile engines, rocket engines, and a variety of other machines.
There are mainly three forms of combustion. Let us study combustion and the many forms of combustion.
What is Combustion?
Combustion is a chemical process that produces heat and light energy by combining a fuel and an oxidant. Combustion is the scientific word for burning.
As the by-products of combustion are heat and light energy these two combine and result in flame. Sometimes, combustion doesn’t produce flame because a flame can be seen only when the fuel or substance that is undergoing the combustion process vaporize.
Combustion is an exothermic reaction represented as:
Fuel (Hydrocarbon) + Oxygen ⇢ Carbon Dioxide (CO2) + Water (H2O) + Heat Energy
Following are the examples of Combustion:
- Combustion of petrol or diesel in a car engine to run a car.
- Burning of LPG to cook and other domestic purposes.
- Burning of the candle to produce a flame.
- Burning of firecrackers.
- Combustion of Hydrocarbons like coal or wood to produce heat in cold conditions.
Combustible Substances: The substances that undergo the process of combustion are known as combustible substances. These substances burn in the presence of air and result in heat and light energy. Combustible substances are often called flammable substances. These substances are capable of burning, igniting, and self-igniting. Combustible substances must be maintained with caution to avoid accidents.
e.g. Petrol, Kerosene, Wood, Charcoal, Diesel, etc.
Types of Combustion
A combustion reaction is divided mainly into 3 types based on how the reaction happens and the products formed. They are:
- Rapid Combustion,
- Spontaneous Combustion, and
- Explosive Combustion.
Rapid Combustion requires external heat energy to start. This reaction results in enormous amounts of light and heat energy. As the name suggests this type of combustion occurs rapidly.
Rapid combustion will take place as long as fuel remains. This combustion process gives flame most of the time and is used in engines that undergo internal combustion. These engines work on the rapid burn which can be adjusted if the mixture inside these engines explodes which is called a Detonation.
Examples for Rapid combustion are,
- Wax candle burns as soon as we give external energy by lightning the match stick.
- Burning of LPG in Gas Stove.
- Kerosene stove working by burning kerosene oil.
Spontaneous Combustion doesn’t require any external energy to start the combustion process, unlike Rapid combustion. This combustion starts spontaneously at room temperature itself due to self-heating.
This reaction starts because of internal oxidation in the substance which leads to the thermal process, If that particular substance reaches its ignition point temperature and has enough oxygen to start the combustion process, the substance starts burning on its own spontaneously. The rise in temperature inside the substance is due to internal reactions which are mostly heat evolving i.e. exothermic. This kind of reaction mostly happens in those substances which have less ignition temperature.
Examples for Spontaneous Combustion are,
- Forest Fires.
- Phosphorous burns spontaneously at room temperature.
- The reaction of Alkali Metals when combined with water.
- Bacterial composting inside organic materials.
- Many accidents in coal mines are due to the spontaneous combustion of coal.
Explosive Combustion happens very rapidly releasing enormous amounts of heat, light, and sound energy. This combustion process is simply can be said as an explosion.
During this combustion, gases that are released will spread quickly resulting in sound energy. Explosive Combustion starts when some energy ignites the substance and heat, light, sound energies release immediately.
Examples for Explosive Combustion:
- Burning of firecrackers and
- Dynamite explosion.
Differences between Rapid and Spontaneous Combustion
Let’s discuss some important differences between Rapid and Spontaneous combustion as,
|Spontaneous combustion takes place spontaneously
|Rapid Combustion must be started by an external source
|No external energy is required
|External energy is required
|Depends on the ignition temperature of the fuel to start the combustion process.
|Depends on external heat energy to start the combustion process
|Less amount of heat energy is released
|A large amount of heat energy is released
|Less amount of light energy is released
|A large amount of light energy is released
|e.g. Phosphorous burns spontaneously at room temperature, Forest Fires
|e.g. Wax candle burns as soon as we give external energy by lightning the match stick, Burning of LPG in Gas Stove.
Problem 1: What is meant by Incomplete Combustion?
The combustion process taking place in less or insufficient supply of oxygen is known as Incomplete Combustion. This type of combustion results in poisonous gases like carbon mono oxide, carbon dioxide. Carbon is usually released in the form of soot in this process. As incomplete combustion results in the formation of harmful gases complete combustion are usually preferred.
Problem 2: What is ignition temperature?
Ignition temperature is the temperature at which the fuel starts burning is known as ignition temperature. Any substance to catch fire must reach its ignition point. Based on the ignition temperatures of a substance the necessary precautions are taken to store the substance. Every substance has different ignition points. For example, the ignition temperature of Ethanol is 365 0C unless and until Ethanol reaches 365 0C.
Problem 3: Define Inflammable substances?
The substances with very less ignition temperature and mostly catches fire easily are known as Inflammable substances. These substances must be stored very carefully since they catch fire spontaneously without any external energy. Inflammable substances are highly combustible with high vapor pressure. Examples of inflammable substances are Kerosene, LPG, Magnesium, Phosphorous.
Problem 4: What are the factors that support the Combustion process?
There are three factors that support the combustion process they are:
- Sufficient supply of oxygen
- Fuel which burns during combustion
- External heat energy or any energy that helps the fuel to reach the ignition point and starts the combustion process.
Problem 5: Define Calorific value?
Calorific value is the value that represents a value of the amount of heat released when one unit of substance undergoes combustion (complete combustion) in the abundant supply of oxygen. It is measured in the units, Joule.
Problem 6: Can we use Sulphur as fuel?
Sulphur is an easily available element in nature and can burn in air to produce heat and light energy but, it is not used as a fuel since it produces harmful gas such as Sulfur dioxide when it burns in air. The resultant gases are poisonous which can cause some serious problems.
Problem 7: How does Spontaneous combustion take place?
Spontaneous combustion takes place without using any external energy. This type of combustion takes place in substances with low ignition points in which many internal reactions like internal oxidation takes place results in heat energy. These internal reactions lead to self-heating and when the temperature hits the ignition point combustion takes place spontaneously.
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