Fuels in Chemistry Meaning Types and Energy Value

Fuels are materials that, when burned, release thermal or chemical energy. This energy is required to carry out a variety of tasks and is either used in its natural state or converted into a usable form of energy with the aid of machinery. Petrol, the fuel used to power cars, is an example of conversion. As it burns, it creates heat energy, which is then transformed into mechanical energy to power the car.

"Energy is neither generated nor destroyed; it is only changed from one form to another," states the first law of thermodynamics. In this instance, fuels are a source of energy and depending on our needs, we use them in various ways. Different types of fuels include substances like gasoline, diesel, coal, etc.

History of Fuels

The burning of wood or sticks by Homo Erectus almost two million years ago is the first recorded usage of fuel. Metal melting has been done with charcoal, a product of wood, since at least 6,000 BCE. Persian chemists invented the crude oil distillation process. Coal became a more popular power source in the United Kingdom after the invention of the steam engine in 1769. Early in the 20th century, oil firms created gasoline as a conventional distillate of petroleum. To convert a larger portion of petroleum into gasoline, thermal cracking was developed in 1913. The current trend is towards renewable fuels, such as alcohol-based biofuels.

Characteristics of Fuel

A fuel is considered to be a good one if it possesses the following characteristics:

• The fuel should be cheap.

• Readily available.

• Should possess high calorific value.

• Should easily burn in the air.

• Should be eco-friendly and should burn out without leaving behind any solid or gaseous waste.

• Easy to store, handle, and transport

Classification of Fuels

Fuels are of two types and are classified based on their origin and their physical state.

1. Fuels Are Further Classified Into 2 Types Based On Their Origin.

• Primary Fuels: Some fuels occur naturally that may be used as an energy source without any chemical processing.

Ex: Peat, Natural gas, Coal, Wood, Crude Oil, etc.

• Secondary Fuels: They are made from primary fuels and only become an energy source after going through chemical processing.

Ex: Kerosene, coke, gasoline, petrol, and diesel.

2. Fuels Are Further Classified Into 3 Types Based On Their Physical State.

Solid Fuels: The term "solid fuel" refers to a variety of solid materials used as fuel to generate energy and provide heating, which is typically released by combustion. Solid fuels are made of wood, charcoal, peat, coal, and pellets composed of cereals like rye, maize, wheat, and charcoal. Solid fuel is also utilised in solid-fuel rocketry. The fuel source for the industrial revolution, used to power everything from steam engines to furnaces, was coal. Steam locomotives were also frequently powered by wood. Today, the production of power still uses both peat and coal.

• Advantages: easier storage and transportation, low cost of manufacture, and moderate temperature for ignition.

• Disadvantages: A significant amount of energy is wasted, Controlling their combustion is difficult and expensive, their burning releases a lot of harmful gases and has a high ash content.

Liquid Fuels: Liquid fuels are energy-producing or combustible substances that may be used to generate mechanical energy, often kinetic energy. The majority of liquid fuels now in use are created by heating dead plants and animals under high pressure inside the Earth's crust, resulting in the formation of fossil fuels. Ex: Petrol, crude oil, diesel, kerosene, etc. However, other kinds fall under the category of liquid fuels, including bio-diesel, ethanol, jet fuel, and hydrogen fuel.

• Advantages: liquid fuels have calorific value, Burn cleanly without ash, the combustion is simpler to manage, have easier transportation through pipelines and loss-free long-term storage, and Energy loss is noticeably less.

• Disadvantages: Compared to solid fuel, the price of liquid fuel is significantly greater, the price of storage techniques is higher, a greater possibility of fire dangers and for more effective combustion, special burning apparatus is needed.

Gaseous Fuels: Gaseous fuels, such as petroleum gas, are defined as fuels that are in a gaseous condition at room temperature. Hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or combinations of these are the main ingredients of many fuel gases. Such gases are potential sources of heat energy or light energy that are easily transferred by pipes from the point of origin to the location of consumption. Gaseous fuels include compressed natural gas, which is delivered through pipes to our house kitchens.

• Advantages: Pipes provide for simple transportation, It's easier to ignite, their heat content is greater, burn without ash and it is a cleaner form of fuel, and specialised burner technology is not required.

• Disadvantages: Requires large storage tanks, due to their high flammability there is an extremely high risk of fire dangers, hence careful safety precautions must be taken.

Fuel Efficiency

Every time a fuel burns, it transforms the chemical energy it contains into kinetic energy. Any work may be completed using this energy. Fuel efficiency is the rate at which a fuel transforms energy. Kilometres per litre is the unit used to measure fuel efficiency. Different fuel types create varying amounts of heat. The quantity of heat a fuel generates is measured and expressed using its calorific value. In other terms, fuel efficiency may be defined as the amount of energy released per unit mass of fuel.

Definitions of Some Important Terminologies Related to Fuel

• Calorific value: The amount of heat released when a unit mass of fuel burns completely in the presence of air or oxygen is referred to as the calorific value.

• Ignition temperature: The minimum temperature needed to initiate or produce combustion is known as the ignition temperature of a material. The ignition point is another name for the ignition temperature. It is the temperature at which anything may ignite and begin to burn.

• Octane Number: The anti-knock rating, or octane number, is a measurement of a fuel's resistance to knocking when ignited in a mixture with air in the cylinder of an internal combustion engine. The octane number is calculated by comparing the fuel's knock intensity under typical conditions with mixes of two reference fuels: iso-octane, which resists knocking, and heptane, which knocks easily. The iso-octane-heptane mixture that matches the fuel being tested in a conventional test engine is what determines the octane number, which is expressed as a volume percentage of iso-octane.

Important Questions

1. What is fuel? Mention a few examples.

Ans: A material that releases heat and energy when burned is called fuel. Various applications make use of the energy or heat that fuels release. Ex: Coal, petrol, diesel, natural gas, wood, etc.

2. Mention a few characteristics of good fuel.

Ans: Good fuel should be cheap, readily available, should possess high calorific value, should be eco-friendly, should burn out without leaving behind any solid or gaseous waste, and should be easy to store, handle, and transport.

Practice Questions

1. The amount of heat released by 1 kg of fuel is called:

1. Fuel value

2. Calorific value

3. Energy value

4. Combustion value

Ans: (b)

2. Fuels that exist as solids at room temperature are known as:

1. Solid fuels

2. Liquid fuels

3. Gaseous fuels

4. Biofuels

Ans: (a)

Conclusion

All of the above-mentioned aspects fall under a broad field of fuel technology. Humans have exploited all non-renewable fuels like fossil fuels from time immemorial. Now, with the rapid depletion of all the natural resources, there is a non-renewable fuel shortage across the globe, resulting in an economical crisis everywhere. To tackle all these issues humans are now looking out for renewable sources of energy like solar, hydro, wind, and geothermal energies and biofuels for sustainability.