Diesel fuel

Diesel fuel, often called diesel or diesel oil, is a liquid fuel designed for diesel engines. These are a specific type of internal combustion engine. Unlike gasoline engines, they do not use a spark to ignite the fuel. Instead, they rely on a process called compression ignition. This happens when the engine compresses inlet air until it becomes very hot. When fuel is injected into this hot, compressed air, it ignites spontaneously.

Because of this mechanism, diesel fuel must have excellent compression ignition characteristics to work reliably.

The most common form of this fuel is petroleum-derived diesel, sometimes called petrodiesel. It is produced in oil refineries through a process called fractional distillation. During this process, crude oil is heated at atmospheric pressure to separate it into different parts. This creates a mixture of carbon chains, typically containing between 9 and 25 carbon atoms per molecule. To improve the fuel, refineries use a method called hydrodesulfurization to remove sulfur.

Because "straight-run" diesel is often in short supply, refineries use cracking technologies like visbreaking and coking. These methods convert heavier, less useful oil fractions into diesel. Finally, refineries may add kerosene to modify the fuel's viscosity, which is its thickness.

Scientists are also developing alternative types of diesel that do not come from petroleum. One major alternative is biodiesel, which is made from vegetable oils or animal fats, known as biolipids. This is created through a chemical process called transesterification. In this process, oils are reacted with methanol to form fatty acid methyl esters, or FAME. In Europe, rapeseed oil is a common source, while soybean oil is frequently used in the United States.

This process often uses catalysts like sodium or potassium hydroxide. It produces biodiesel along with byproducts like glycerine and water, which must be removed. Another type is synthetic diesel, which can be made from natural gas. This uses the Fischer–Tropsch process to convert synthesis gas into a fuel that is mainly paraffins with low sulfur content.

The history of diesel fuel begins with the German inventor Rudolf Diesel. Around 1892, he invented the compression-ignition engine. Diesel originally believed his motor could run on almost any fuel in any state of matter. His early experiments involved crude oil from Pechelbronn, but he found it too viscous, or thick. He moved on to testing kerosene, petrol, and various types of lamp oil.

In 1898, production engines in Scotland and France used shale oil because other options were too expensive. Diesel even tested a coal-dust prototype in December 1899. However, the coal dust caused piston rings to fail after only a few minutes of use.

As engine technology advanced, fuel quality became more important. In the 1930s, the introduction of motor-vehicle engines like the Mercedes-Benz OM 138 required higher-quality fuels. Before standardization, engines often ran on cheap fuel oils or mixtures of petrol and kerosene. After World War II, the first modern high-quality standards were introduced, such as DIN 51601. By 1993, the EN 590 standard replaced older rules in the European Union. Today, most diesel in North America and Europe is ultra-low-sulfur diesel (ULSD). This type has substantially lowered sulfur content to meet modern requirements.

To keep different fuels safe, many regions use specific colors for storage. In the United States, diesel is often kept in yellow containers to distinguish it from blue kerosene containers or red petrol containers. In the United Kingdom, diesel is normally stored in black containers. This helps prevent people from putting the wrong fuel into a vehicle.

In some places, like the UK, a specific type called "red diesel" is used for agriculture and contains an identifying dye. This helps authorities differentiate it from "white diesel," which is used for road vehicles. In Indonesia and parts of the Middle East, the fuel is often called Solar.

Chemical additives are also used to ensure the fuel works well in different environments. For example, ethylene-vinyl acetate (EVA) is added as a "cold flow improver." Adding between 50 and 500 ppm of EVA helps prevent wax crystals from blocking fuel filters in cold weather. Other additives, such as antioxidants and antifoaming agents, are added at much lower levels, between 5 and 50 ppm. These additives help manage the specific chemical composition of the fuel.

While diesel is essential for heavy trucks and many industries, it is important to note that diesel exhaust, especially from older engines, can cause health damage.