Diesel vs Petrol: What Are the Differences?

“These gas prices!” We’ve been bemoaning the horrors of gas prices on a global scale since the Ukraine crisis started. Yet, most of us didn’t pay as much attention to diesel fuel and its prices.

Both conventional diesel and gasoline are derived from mineral oil. However, their refining processes differ.

Diesel is in theory simpler to refine than gasoline. But, it includes more impurities that must be eliminated before it can achieve the same emission standards as gasoline.

Diesel contains more energy per liter than gasoline. And the engine combustion process is more efficient. It results in greater fuel economy and reduced CO2 emissions when you use diesel. If you’ve never understood the differences between petrol (which is gas) and diesel fuel, no worries. 

Keep on reading for our full breakdown of the diesel vs petrol debate and how each comes with its pros and cons.

Diesel vs Petrol: What Are They?

Petrol, a liquid mixture obtained from petroleum, is mostly made up of aliphatic hydrocarbons and is fortified with aromatic hydrocarbons like toluene, benzene, or iso-octane to increase its octane rating. Its primary use is as a fuel for cars and trucks with internal combustion engines.

Diesel, which is used as a fuel in diesel engines, is a fractional distillate of petroleum fuel oil or a “cleaned” sort of vegetable oil. It was devised by German engineer Rudolf Diesel.

Diesel and Petrol Engines: Similarities and Differences

By virtue of the combustion process and the overall engine design, a diesel engine may be up to 40 percent more efficient than a spark-ignited gasoline engine. Even one with the same power output, everything else being equal, especially with modern “low” compression types of diesel.

Diesel fuel has a calorific value of around 45.5 MJ/kg, which is somewhat lower than gasoline’s 45.8 MJ/kg. Diesel fuel is denser than gasoline and carries about 15% more energy per volume (around 36.9 MJ/liter against 33.7 MJ/liter). Even after accounting for the difference in energy density, the diesel engine’s total efficiency is around 20% better than that of the gasoline engine.

Depending on the precise composition of the fuel, 1 liter per 100 km translates to around 26.5g CO2/km for diesel and 23g CO2/km for gasoline.

Petrol Fuel vs Diesel Fuel: Refinery Processing

Crude oil comprises hundreds of distinct kinds of hydrocarbons. And, depending on the crude oil’s source, a variety of contaminants.

To generate gasoline, diesel, or any other oil-based products, the hydrocarbons must be separated by one or more types of refining.

Different chain lengths of hydrocarbons have increasingly higher boiling points as the chain length increases. Therefore they can all be separated by fractional distillation.

During the process, crude oil is heated in a distillation column. And, the various hydrocarbon chains are extracted as a vapor. Then, manufacturers recondense them according to their vaporization temperatures.

Gasoline is composed of a mixture of alkanes and cycloalkanes with chain lengths ranging from 5 to 12 carbon atoms. These boil between 40 and 205 degrees Celsius.

Gas oil and Diesel are produced from alkanes with 12 or more carbon atoms. These have a boiling point between 250 and 350 degrees Celsius.

Processes for Transforming Fractions

Various strategies are used to transform certain fractions into others after distillation. There’s cracking, which is the process of separating big hydrocarbon chains into smaller chains.

Then, we have unification. It’s the process through which smaller hydrocarbon chains are combined to form bigger ones. Finally, there’s alteration. It’s the rearrangement of several isomers to produce desired hydrocarbons.

This enables a refinery, for instance, to convert diesel fuel into gasoline fuel, depending on the demand for gasoline. Additionally, refineries blend multiple fractions (processed and unprocessed) to create the required products.

Different combinations of hydrocarbon chains, for instance, may produce types of gasoline with varying octane ratings.

You’ll want to eliminate impurities. They include organic molecules containing sulfur, nitrogen, oxygen, water, dissolved metals, inorganic salts, and fractions. These need manufacturers to distill them and chemically process and treat them.

Differences in Chemical Composition

Diesel consists of about 75% saturated hydrocarbons. It’s mainly paraffins, such as n, iso, and cycloparaffins. Also, 25% aromatic hydrocarbons such as naphthalenes and alkylbenzenes.

Standard diesel fuel has the chemical formula C12H23, while variants between C10H20 and C15H28 are possible. The hydrocarbon molecules that make up gasoline have anywhere from 5 to 12 carbons. But it’s a mixed bag depending on where you use it.

A normal gasoline sample consists mostly of paraffins (alkanes), aromatics, naphthenes (cycloalkanes), and olefins. The ratios fluctuate depending on several variables.

Comparing the Volatility and Energy Content

Petrol is more volatile than diesel. Not only due to its fundamental components but also due to the additives that are added.

Petrol/Gasoline has around 34.6 megajoules per liter (MJ/l)while diesel contains about 38.6 megajoules per liter. This increases the power of diesel.

Applications of Gasoline and Diesel

Diesel is used to power diesel engines used in automobiles, trucks, motorcycles, etc.

Some diesel variants are also utilized to power residential heating systems. In the liquid-liquid extraction of palladium from nitric acid mixtures, poor-quality (high-sulfur) diesel fuel has been used as an extraction agent. Primarily, gasoline is used to power gasoline engines in automobiles, motorcycles, etc.

As an airplane fuel, paraffin, a byproduct of crude oil generated between 190 and 250 degrees, is used.

Car Engines: Which Is Better?

There is no straightforward response to this question. For some individuals, diesel is the ideal alternative, whilst for others, gasoline is preferable.

According to experts, a diesel vehicle is not cost-effective until the annual mileage is 10,000 miles in a used vehicle or 6,000 miles in a new vehicle. But, for a truck, it’s a great choice. You can even buy diesel fuel in bulk.

If your annual mileage is less than this or if you just expect to retain your car for a few years, you may be better off with a gasoline-powered vehicle.

Petrol Fuel and Diesel Fuel: A Closer Look

Most of us in North America don’t recall the existence of diesel fuel, unless we’re involved in the trucking and transport business. However, our European friends have been taking advantage of the power of diesel fuel for decades on end.

We hope that our diesel vs petrol comparison has shed some light on the nuances of both kinds of fuel. This way you can make a better purchasing decision for your wallet and the environment. 

Next, you’ll want to check out our automotive section for more tips and advice on how to take care of your engine regardless of the kind of fuel it needs.

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