Combustion Fuels

Introduction

Combustion is a chemical phenomenon that generates heat when a material reacts fast with 𝑂2. The starting substance is known as the fuel, while the 𝑂2 flow is referred to as the oxidizer. The fuel can be solid, gaseous, or liquid, although, for aeroplane propulsion, the liquid is most usually used. The oxidizer can also be a liquid/vapour/solid, though it's usually gas in planes. In model rockets, solid fuel along with oxidizers are used.

Heat Produced On Combustion of Fuels

The heat value of a fuel is the heat energy emitted during combustion. The heat value of fuel also referred to as the calorific value, is an evaluation of its energy density expressed in energy/mass.

What is Combustion?

Combustion is a chemical phenomenon that produces heat when a substance reacts with oxygen. A material that burns is referred to as fuel, and it can be solid/gaseous/liquid.

Types of Combustion

• Rapid Combustion − When a vapour burns quickly, releasing heat and light. Rapid combustion is the term for this type of combustion.

• Spontaneous Combustion − Spontaneous combustion occurs when a substance spontaneously goes up in flames without any external trigger.

• Complete combustion − Full combustion is described as the entire combustion of a fuel and 𝑂2 mixture with no remaining fuel, high enough temperature along with friction to activate all of the fuel constituents.

• Partial combustion due to insufficient air-fuel mixing, a lack of residence time, a lack of temperature, and a lack of complete surplus air.

• Explosion − When a rapid reaction occurs, resulting in the discharge of heat and light as well as the release of a significant volume of gas. It's known as an explosion.

Combustion Reaction

A combustion process occurs when a substance reacts quickly with 𝑂2. Combustion is commonly referred to as "burning," and the substance the burns is called "fuel."

$\mathrm{CO_{2}}$ along with water vapour are the byproducts of a full combustion process. In the majority of cases, the reaction creates both light and heat. The general equation for a complete combustion process is:

$$\mathrm{Fuel\:+\:O_{2}\:\rightarrow\:CO_{2}\:+\:H_{2}O}$$

Fuel

Fuels are sources of heat energy for home and industrial applications. They assist us in meeting our daily requirements. A good fuel is easy to come by. It is inexpensive and burns at a modest rate in the air. It generates a significant quantity of heat. It does not leave any unwelcome chemicals behind.

Types of Fuels

• Wood & coal are examples of solid fuels. In the household, they are used to cooking meals. Coal is also used in the manufacturing industry.

• Liquid Fuels − Kerosene and gasoline are two examples. To prepare food, kerosene is used in stoves.

• Gaseous Fuels − In industries, fuels such as petroleum gas along with natural gas are employed. Automobiles operate on compressed natural gas (CNG).

Fuel Efficiency

When 1 kg of fuel is entirely burned, the calorie content is the amount of heat energy created. A fuel's calorific value is measured in kilojoules per kilogram (kJ/kg). Efficiency refers to the percentage of a combustion's energy that is converted into useful work. Its effectiveness is proportionate to its size.

Characteristics of an Ideal Fuel are

• The ideal fuel should be cheap, easy to obtain, and flammable.

• It needs to be high in calorific value

• It has no negative impact on the environment due to the absence of hazardous gases or residues.

• Because dry fuel has a higher calorific value, it should be dry and minimal in moisture.

Flame

The visible and vaporous part of a fire is the flame. Flames are created when chemicals evaporate during combustion. Kerosene oil as well as molten wax, for instance, ascends through the wick and is evaporated throughout the burning process, resulting in flames. Since charcoal does not evaporate, it does not form a flame.

Structure of flame

• Outer Zone − The outermost zone, which is the hottest of all the regions, is blue. Due to total combustion, this is the case. It's the section of the flame that doesn't glow.

• Middle Zone − The central zone of the candle flame is fairly hot & yellow, indicating incomplete fuel combustion. It's the most visible part of the flame.

• Innermost Zone − The flame's innermost region is the coolest and is black. This is because there are unburned wax vapours present.

Burning of Fuel leads to Harmful Products

• 𝐶 fuels emit unburned carbon particles, which are fine and harmful contaminants that can trigger respiratory problems including asthma.

• The partial combustion of these fuels produces 𝐶𝑂 . It is a very deadly gas that, if discharged in a room, can kill a human sleeping inside.

• The majority of fuels emit carbon dioxide into the atmosphere when they are burned. Global warming is caused by an increase in carbon dioxide levels in the atmosphere.

• Petrol engines emit Nitrogen oxides. Acids are formed when Sulphur and Nitrogen oxides dissolve in rainfall. Acid rain is the name for this type of rain.

Conclusion

It can be concluded that combustion is a chemical phenomenon that produces heat when a material reacts with oxygen. Heat is produced during the combustion as the fuel and oxidizer are converted into exhaust products. A material that burns is referred to as combustible or fuel and it can be solid/ liquid/gaseous. Three things are required for combustion to happen: a fuel to be ignited, a supply of oxygen, and a heat source. Exhausts are produced and heat is emitted as a result of combustion.

FAQs

1. What are the conditions for combustion?

Combustion requires the following conditions −

• The presence of flammable material, a fuel, as well as a combustion promoter.

• Raise the ignition temperature of the flammable chemical and sustain it.

• The availability of 𝑂2.

2. What are Non-combustible & Combustible substances?

Combustible materials, like wood, are easily combustible, whereas non-combustible substances, such as sand, glass along with water, and, are not easily combustible.

3. What are fuel efficiency as well as calorific value?

The quantity of heat energy generated when 1 kg of fuel is entirely burned is referred to as the calorific value of the fuel. A fuel's calorific value is measured in kilojoules per kilogram (kJ/kg). The fraction of energy generated by a combustion process that is turned into meaningful work is called efficiency. Its effectiveness is proportionate to its size.

4. At what temperature does combustion occur?

It will combust and burn at a temperature of 424 to 475⁰F on average (218 and 246 ⁰C).

5. Combustion and burning the same things?

The terms "burning" and "combustion" are frequently interchanged. The development of a flame is the primary distinction between burning and combustion. Burnings are combustion processes that result in a flame. Burning and combustion, on the other hand, both create heat energy.