Fuels: The Stuff that Runs the World

To run vehicles, mechanical energy is required and is generally not available freely. Energy has to be converted somehow from another form by some intermediate action. For some machines, this task is carried out by ‘engines’ and these engines are powered by various types of “Fuels”. In this article, we shall see what fuels are and the different types of fuels.

Fuel Guage

Fuel Gauge (Image source: sxc.hu)

What are fuels?

Fuels are combustible chemical compounds which undergo compression and combustion by certain mechanisms to supply power to their corresponding machines. A normal reaction taking place in fuel would be converting its chemical energy to mechanical energy. This mechanical energy can be converted to electrical energy by generators or simply used by vehicles. Based on general requirements like power, torque, economy, mileage and engine type, there are many fuels which are in use today. For example, in a rocket, one requires more power rather than economy (which is a secondary goal) and hence uses oxygen and helium as they are easily combustible. Let us look into the type of fuels in existence today.


1.      Fossil Fuels
Fuel Pumps

Fuel Pumps (Image source: sxc.hu)

Fossil fuels are “hydrocarbon” (chemical compounds containing carbon and hydrogen as their primary constituents) derived compounds. They attain their name as they are formed from fossils under high heat and pressure over millions of years. These fuels are generally in liquid, solid and gaseous form. The famous example and the most popular fuel in the automobile industry in the world, petroleum (petrol and diesel) is a fossil fuel. Fossil fuels are popular because of their ease of combustion when they are heated. Once combusted, they begin to expand rapidly. This compression and expansion are used to move pistons which rotate shafts and transfer energy. Being  used in the automobile industry widely, they are also used  in various machines in industries, and in generators. Coal is another well-known fossil fuel which is used in electric power generation and was used to run train engines once upon a time.


Some of the drawbacks of fossil fuels are the pollution factor and its limited availability. As they take millions of years to form, they are practically non-renewable. Today, the fuel reserves are running low giving a necessity to the rise of renewable energy fuels. (Read different types of energy sources)


2.      Nuclear Fuels

Nuclear fuels occur in the solid state. They have a property of disintegrating into the consequent entities by the processes of either “nuclear fusion” or “nuclear fission”. While disintegration, they release a lot of energy that can be used to evaporate water to generate steam, which in turn rotates turbines to generate energy in the required form (generally electrical energy is produced from this method).


3.      Alternate Fuels

Since the above mentioned fuels are running low on reserves, the necessity to use an alternate source of fuel is required. Alternate fuel can be formed by renewable resources, such as CNG (Compressed Natural Gas) or electrical batteries which can be recharged and reused. Solar fuel cells (constituents of solar panels) consist of light sensitive equipment which captures the energy trapped in the photons present in the sun light to produce electricity. The problem with following the “clean and green” system is that it is expensive to install such a system and can power a limited amount of equipment. Although it is slightly expensive to install, one has to know that it is a one-time payment and will have a guaranteed service throughout its lifetime. It will also encourage a clean and hazard free environment in which many generations of humans can live happily on.


Now that we have studied the types of fuels, let us go into its applications by understanding its most common application, in ‘Vehicles’. We shall see the role played by fuels in engines and compare the two most common fuels in today’s automobile industry “Petrol” and “Diesel”.


Role of Fuel in Engines

The role of the engine of the vehicle is to provide a counter reaction to the force which prevents the vehicle from moving. For example, for an aircraft to fly forward, it has to resist the wind resistance that moves it back and the weight which pulls it down. To produce these opposing forces, the engine of the vehicle must have some energy in order to complete the work. This energy comes from burning fuels. Let us look a car engine.


It consists of a certain number of cylinders (1 in TATA Nano to 8 in Bugatti Veyron, some even have 12 or 16). These cylinders are the hearts of a vehicle. Inside the cylinders, pistons are placed which are interconnected by a common shaft called the “Crankshaft”. The fuel is mixed with air in units called “carburettors” and is sprayed into the cylinder and compressed by the pistons. When the piston reaches a certain point a ‘spark’ is provided by “Spark Plugs”. This causes a small explosion of the fuel-air mixture and suddenly expands and sends the piston down again. The burnt gas is sent out as exhaust and brings the piston back up again. This cycle keeps repeating again and again and causes the up and down motion of the piston. This is transferred to the “Crankshaft” from all the pistons in all the cylinders. The crankshaft transfers this energy to a flywheel which transfers it to the transmission system (gear box) and from there to the wheels of the vehicle with the help of ‘shafts’ and ‘gears’.And this is how a car runs.


There are ‘Petrol’ cars and ‘Diesel’ cars. Why these different fuels? Where does which fuel find more importance and why?


Petrol vs. Diesel

Both are made from petroleum using different compositions of different hydrocarbons. Most people prefer petrol cars now days because they are smoother. Let us look at their properties. One of the main contrasts is that a diesel engine does not require a spark plug. The temperature at compression is sufficient for diesel to combust (lower boiling point as compared to petrol). Therefore you never find a spark plug when you look in a diesel engine. The main advantages of diesel are the higher torque and power production, which allow the engine to support a larger load and also its lower cost per litre (in India). But the difference can be noted in winters as the cold weather causes problems for the vehicle to start (since the engine doesn’t use a spark plug). Here the petrol engine gains the upper hand as it is more efficient. A petrol engine also starts up faster and therefore can reach top speeds in less time. Its ability to support heavier loads allows the optimum usage of diesel in transportation vehicles and heavy motor vehicles (example trucks, vans, autos etc.). Diesel is also used as fuel in ships and trains. Petrol is the more accepted fuel in cars but diesel is not far behind and is becoming popular now days. Diesel engines are most commonly used by the luxury car manufacturer “BMW” using new and innovative technologies to provide the qualities of a petrol engine in a diesel car.