Both petrol and diesel are derived from fossil fuels and are generally called crude oil. Crude oil and natural gas are found deep underneath the earth’s surface trapped in deposits surrounded by layers of rock. They are found typically between 1 mile to where some of the deepest deposits can go down as much as 6 miles. Petroleum refers to liquid crude oil as well as natural gas and the solid state of fossil fuel called bitumen. This article covers the difference between petrol and diesel.
Crude oil extraction
It all starts with the extraction of crude oil which consists of long linear chains or circular chains of hydrocarbon molecules. The combustion of these hydrocarbons provides energy for the engine.
After the oil is extracted, it is fed into a furnace and heated. This heating distills the crude oil and evaporates it in the furnace. From here it enters the fractioning column tower where it condenses into a liquid again and is collected. This process is called fractional distillation where crude oil is fractionalized, and different regions can be observed. The longer chain hydrocarbon molecules have a higher boiling point and can be found at the bottom of the column tower. The fractioning column tower has different temperature regions where it is hotter at the bottom than at the top. Longer hydrocarbon chains need more heat to break down which is why the furnace is hotter at the bottom. These fractions or different layers formed in the fractioning column allow the extraction of various fuels from crude oil.
The difference between petrol and diesel is the length of their hydrocarbon chains which will be discussed below:
Petrol
At the top of the furnace, you will find lighter fuels where the hydrocarbon chains are shorter. These shorter chains have a lower boiling point (between 40 degrees Celsius and 205 degrees Celsius) and will ignite faster and more violently and burns faster. The boiling point of such a chain is proportional to its length or size.
Diesel
In the middle part of the furnace, you will find heavier longer chained hydrocarbons with higher boiling points (between 250 Celsius and 350 Celsius). Diesel is denser than petrol and has more hydrocarbons and thus has more energy per volume.
What is found at the bottom of the furnace?
The bottom of the fractioning tower has the densest compounds and thus the longest chain of hydrocarbons. These dense compounds are usually used as lubrication oil and wax and right at the bottom, the distillate is used for asphalt and industrial fuel oil.
For interest’s sake, jet fuel distillate is between the petrol column and the diesel column.
Which is better, petrol or diesel cars?
Vehicles that use diesel are more economical for the reason that diesel will burn much slower than petrol. This is because it is much denser, and a lower boiling point means less flammable. Diesel engines also produce much more torque (power) than petrol engines because of their efficiency. Petrol engines will produce less torque but higher RPM (revolutions per minute) than diesel engines because of their lower boiling point and fast burn characteristics. Petrol engines ignite the petrol only with a spark (sparkplug). Diesel is not nearly as flammable as petrol and a diesel engine needs to compress the air first before injecting the diesel. Compressed air increases the combustion rate and achieves a higher temperature of the flame. The amount of mechanical energy produced from the same amount of fuel in a diesel engine is much more than a petrol engine and thus more economical. To deal with all that torque, diesel engines must be built much stronger than petrol engines and resulting in bigger and heavier engines.
Diesel engines vibrate more than petrol engines, this is because diesel fuel ignites under pressure (compression) compared to a spark. For this reason, diesel fuel burns rather than ignites. This burn is less controllable and burns unevenly and causes diesel knock. Diesel knock is where excess diesel burns in the compressed air and diesel mixture.
All these vibrations cause more wear and tear to the engine parts and diesel vehicles require more maintenance and must be serviced more regularly.
So which is better, petrol or diesel cars? Well, it all depends on what you need, petrol cars still outperform diesel cars with acceleration and speed although the difference is getting smaller with technology getting better. Turbocharged diesel engines almost perform as well as petrol engines. Fuel efficiency is better in a diesel engine and if you need a vehicle with good torque, you need a diesel engine.
What about greenhouse gases?
Another difference between petrol and diesel is that burning diesel fuel creates a thick cloud of black smoke called smog and soot. The resulting smog of diesel combustion causes acid rain while inhaling the soot (black particles from incomplete combustion) can be dangerous to our lungs. skin and eyes.
Petrol engines are no angels, the combustion of petrol causes a release of greenhouse gasses (carbon dioxide and carbon monoxide) into the air.
Conclusion
Diesel is denser than petrol and ignites more slowly and for this reason, diesel engines are ideal for steady movement. Diesel engines need to be stronger in structure because of the way diesel is ignited and this causes diesel engines to be larger and heavier and suitable for bigger vehicles. Vehicles that carry loads that need steady motion and lots of torque like trucks.
Petrol engines are found in smaller vehicles like cars and bikes and give them the ability to accelerate much faster and generate more RPMs and go faster.
Diesel and petrol are both important for the functioning of all kinds of industries worldwide, at least until diesel and petrol engines are replaced by electric engines for instance.
P.S. Times are changing fast and technology is getting better all the time. The difference between petrol and diesel cars is getting less and less Now even sports cars using diesel engines like Porsche, Jaguar, BMW, Mercedes, Audi, etc.
