What Is Combustion Fuel Definition Types and Calorific Value
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 Fuels in Chemistry Explained Clearly
1. What is a combustion fuel in chemistry?
A combustion fuel is a substance that reacts with oxygen in a combustion reaction to release energy in the form of heat and often light. In chemistry, fuels are typically carbon-containing compounds such as hydrocarbons.
- A combustion fuel reacts with O2 (oxidation).
- The reaction is usually exothermic.
- Common examples: methane (CH4), propane (C3H8), gasoline (mixture of hydrocarbons), coal (mostly carbon).
2. What is the general equation for the combustion of a hydrocarbon fuel?
The general equation for the complete combustion of a hydrocarbon is CxHy + O2 → CO2 + H2O (balanced appropriately).
- Carbon forms CO2.
- Hydrogen forms H2O.
- Example (balanced): CH4(g) + 2O2(g) → CO2(g) + 2H2O(l).
3. What is the difference between complete and incomplete combustion?
The difference between complete combustion and incomplete combustion is the amount of oxygen available and the products formed.
- Complete combustion: Occurs in excess oxygen and produces CO2 and H2O.
Example: 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l). - Incomplete combustion: Occurs in limited oxygen and produces CO and/or C(s) (soot) plus water.
Example: 2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(l).
4. Why is combustion an exothermic reaction?
Combustion is exothermic because the energy released when new bonds form in products is greater than the energy required to break bonds in reactants.
- Bonds broken: C–H, C–C, and O=O bonds.
- Bonds formed: Strong C=O bonds in CO2 and O–H bonds in H2O.
- Net result: Release of heat (ΔH < 0).
5. What is the enthalpy of combustion?
The enthalpy of combustion (ΔHc) is the heat change when one mole of a substance is completely burned in oxygen under standard conditions.
- It is usually negative (exothermic).
- Units: kJ mol-1.
- Example: For methane,
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l),
ΔHc ≈ −890 kJ mol-1.
6. How do you balance a combustion reaction equation?
To balance a combustion reaction, balance carbon first, then hydrogen, and finally oxygen.
- Step 1: Balance C atoms to form CO2.
- Step 2: Balance H atoms to form H2O.
- Step 3: Balance O atoms by adjusting O2.
- Example (ethane):
Unbalanced: C2H6 + O2 → CO2 + H2O
Balanced: 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l).
7. What are the main types of combustion fuels?
The main types of combustion fuels are solid, liquid, and gaseous fuels.
- Solid fuels: Coal, wood, coke.
- Liquid fuels: Petrol (gasoline), diesel, ethanol.
- Gaseous fuels: Methane (CH4), propane (C3H8), hydrogen (H2).
8. What are the products of hydrogen combustion?
The combustion of hydrogen produces only water (H2O) as the product.
- Balanced equation: 2H2(g) + O2(g) → 2H2O(l).
- No carbon dioxide is formed because hydrogen contains no carbon.
- The reaction is highly exothermic.
9. Why does incomplete combustion produce carbon monoxide?
Incomplete combustion produces carbon monoxide (CO) because there is insufficient oxygen to fully oxidize carbon to carbon dioxide.
- Limited O2 prevents formation of CO2.
- Carbon is partially oxidized to CO.
- Example: 2C(s) + O2(g) → 2CO(g).
10. How do you calculate the heat released during combustion?
The heat released during combustion is calculated using q = n × ΔHc, where n is moles of fuel burned and ΔHc is enthalpy of combustion.
- Step 1: Calculate moles (n = mass ÷ molar mass).
- Step 2: Multiply by ΔHc (kJ mol-1).
- Example: Burning 0.5 mol of methane with ΔHc = −890 kJ mol-1:
q = 0.5 × (−890) = −445 kJ.
