Petrol vs. Diesel: The Difference Between These Fuels and How They’re Made
Have you ever pulled into a gas station and wondered what the difference was between diesel fuel and petrol fuel or how they are even made? Despite both fuel types originating from the same source—crude oil—there are several key differences in the creation and usages of diesel and petrol fuels. This guide will give you the topautotools rundown on the difference between petrol and diesel.
What is Petrol Fuel?
Petrol is the most popular type of fuel, powering the majority of transportation needs throughout the world. Also known as gasoline, petrol is a hydrocarbon derived from crude oil. When in its natural state, petrol is a liquid with a distinctly strong odor.
Petrol works with internal combustion engines and has a rating system that is based on octanes. In general, the average octane rating is either 91 or 92. Gas stations typically offer premium fuels that have octane levels reaching up to 98. Higher octane levels generally have additives, which act as “lubricants” to lessen the wear and tear on engines.
How is Petrol Made?
Petrol begins as crude oil found deep within the earth’s surface. Whether on dry land or the ocean floor, companies can dig as deep as 1,000 feet or more to find crude oil. Special equipment is used to drill into the ground to find the crude oil. Once discovered, the drill is then removed from the ground and replaced with a pipe that will extract it.
Crude oil, in its natural state, needs to go through the following processes in order to be made into the petrol used in cars and trucks:
Fractional Distillation
The first step in creating petrol from crude oil is to separate the large chains of molecules from the small chains of molecules. This process is called fractional distillation and it takes place in a fractional distillation tower where the oil is pumped into and then exposed to extreme heat (over 600°F).
During this process, the largest molecules will end up evaporating and vapors will rise to the top of the tower. Within the tower, gasoline, natural gas, and kerosene will be released at the top. Meanwhile, the bottom of the tower will have various lubricants.
Refining Process
The next step is called the refining process which is done to create a chemical change by using a catalyst, pressure, and high temperatures. The catalysts that are used include acid, processed clay, platinum, and aluminum. These all work together in order to break down the larger molecules.
Additives
After the refining process is done, the next step is to mix in additives in order to prevent the petrol from burning too fast and causing damage to the engine. The petrol is then ready to be rated by octanes. The higher the octane level, the higher the quality.
What is Diesel Fuel?
Diesel fuel is any liquid fuel used in diesel engines, which use fuel ignition without a spark, thanks to the compression in the inlet air mixture and the injection of the diesel fuel. Named after Rudolf Diesel, who experimented with these engines in the late 1800s to early 1900s, diesel fuel is a widely used source of petroleum fuels throughout the world. It’s common in boats, trains, trucks, barges, buses, fuel construction, farm equipment, military vehicles, some cars, in generators to produce electricity, in heating systems, and more. There are even some remote villages/towns that rely on diesel to power their electricity.
The most common type of diesel fuel is called petrodiesel, which is diesel fuel derived from petroleum. There are also a few non-petroleum diesel alternatives like biodiesel, synthetic diesel, and biomass to liquid.
How is Diesel Fuel Made?
Diesel fuel starts its cycle as crude oil that needs to be harvested. Once it has been harvested, it’s then transported to a refinery where it will go through three specific processes:
Separation
The first process is called separation. During this stage, the crude oil is placed in distillation towers that have extreme amounts of heat at a range of 200°C and 350°C. This heat causes the crude oil to separate into liquid and gas.
The top of the tower is a different temperature than the bottom, which is how the separation is made possible. In the top of the tower will be propane gas, the middle of the tower is where diesel is found, then the bottom of the tower is all the lubricants.
Conversion
The next step in the process is called conversion, which has a catalyst used on the heavier oils. This step is able to create additional propane, diesel, and gasoline.
Purification
The last step in the process is called purification, which exposes the gasoline, diesel, and propane to a catalyst and hydrogen in order to remove the sulfur. Once the diesel fuel passes inspections and tests, it is ready to be sent through the pipelines.
Differences Between Petrol and Diesel
As mentioned, despite both fuel types being created from crude oil, there are many differences between the two. The following is a list of some of the more notable differences between petrol and diesel:
- Petrol is more volatile, more flammable, less dense, and lighter than diesel.
- Diesel has more energy per gallon, which translates into diesel-powered vehicles getting more miles per gallon than petrol.
- Petrol has higher levels of CO2 and carbon monoxide than diesel, but does not produce Suspended Particulate Matter like diesel.
- Diesel-powered vehicles have more torque and run at lower speeds where petrol runs at a higher RPM.
- Diesel viscosity increases at lower temperatures where petrol doesn’t change at all.
Ultimately, diesel fuel is best suited for larger cars, 4WD trucks and SUVs, or automobiles with higher consumption. Petrol is best suited for smaller, compact cars with lower consumption.
About the Author: Charles Martin
Charles is a former auto/moto technician and mechanic who has written for several automotive related websites including topautotools, which he co-founded. Charles’s favorite car is the 1966 Shelby 427 Cobra and enjoys writing about anything auto related including the best tools and tips to help everyday people in life make good decisions about anything automotive related.
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