Diesel fuel

Diesel fuel, also called diesel oil or fuel oil, is a special kind of liquid fuel made for use in diesel engines. Diesel engines are a type of internal combustion engine where the fuel catches fire because of very high pressure, not because of a spark. Because of this, diesel fuel needs to work well when squeezed very tightly.

The most common diesel fuel comes from petroleum, a material made from oil refineries. But there are also other types of diesel fuel that do not come from petroleum, such as biodiesel, biomass to liquid (BTL), and gas to liquid (GTL) diesel. In many places, rules decide what diesel fuel must be like. For example, in the European Union, diesel fuel must meet the EN 590 standard. Most diesel fuel today has very little sulfur in it, which is called ultra-low-sulfur diesel (ULSD).

Even though diesel fuel is made for diesel engines, it can sometimes be used in other kinds of engines, like the Akroyd engine, the Stirling engine, or even in boilers for steam engines. Diesel fuel is often used in heavy trucks, but the smoke from diesel engines, especially older ones, can be bad for health.

Names

Diesel fuel is often just called diesel. In the United Kingdom, it is also known as white diesel to differentiate it from a special type of fuel for farming called red diesel. The official name for white diesel in the UK is DERV, which means diesel-engine road vehicle.

In Australia, diesel fuel is sometimes called distillate, and in Indonesia and much of the Middle East, it is known as Solar, a name from the country’s main oil company Pertamina. The term gas oil is also used in some places, including France, where it is called gazole.

History

Origins

Diesel fuel began with tests by a German inventor named Rudolf Diesel for his special engine, called a compression-ignition engine, which he created around 1892. At first, Diesel wasn’t sure what fuel to use. He thought his engine could work with many kinds of fuels. The very first engine models only used liquid fuels.

Diesel first tried crude oil from a place called Pechelbronn, but later switched to petrol and kerosene because crude oil was too thick. Kerosene became the main test fuel. He also tried different kinds of lamp oil, ligroin, coal tar, creosote, paraffin oil, more petrol, and fuel oil, and they all worked. In Scotland and France, people used shale oil in the first Diesel engines made in 1898 because other fuels were too costly. In 1900, a French company made a Diesel engine shown at big fairs, and it ran on peanut oil without needing any changes.

Since the 20th century

Before diesel fuel had set rules, diesel engines often used cheap oils. In the United States, these came from petroleum, while in Europe, they used coal-tar creosote oil. Some engines used mixes of fuels like petrol, kerosene, rapeseed oil, or lubricating oil because these were cheaper and not taxed at the time. When cars with diesel engines, like the Mercedes-Benz OM 138, appeared in the 1930s, the fuel needed to be better. After World War II, modern high-quality diesel fuels were created, following rules like DIN 51601 and later EN 590 in Europe. On ships, cheap heavy fuel oils, sometimes called Bunker C, are still used today, especially since fuel prices rose in the 1970s because of the 1970s energy crisis.

Types

Diesel fuel comes from different sources, with the most common being petroleum. Other sources include biomass, animal fat, biogas, natural gas, and coal liquefaction.

Petroleum diesel

Petroleum diesel is the most common type of diesel fuel. It is made by heating crude oil and collecting a certain part of it. This part usually has small molecules with carbon chains of different lengths. To improve it, the fuel goes through a process to remove harmful substances.

Sometimes, there isn’t enough of this type of diesel, so refineries mix in other materials. They use special processes to change heavier oils into lighter ones that can be used as diesel. They also add kerosene to change how thick the fuel is.

Synthetic diesel

Main article: Synthetic fuel

Synthetic diesel can be made from many things, but natural gas is the most important. The raw materials are turned into a mix of gases, which is then changed into synthetic diesel through a special process. This type of diesel usually has very little harmful content and is often mixed with regular petroleum diesel.

Biodiesel

Main article: Biodiesel

Biodiesel comes from vegetable oil or animal fats. These oils go through a process to turn them into fuel. The most common oils used are rapeseed oil in Europe and soybean oil in the US. Biodiesel can be used by itself in some engines or mixed with regular diesel. It follows special standards to make sure it works well as fuel.

Storage and additives

In the US, diesel fuel is best kept in a yellow container. This helps people tell it apart from kerosene, which is usually in blue containers, and petrol ("gasoline"), which is often in red containers. In the UK, diesel is usually stored in a black container, different from unleaded or leaded petrol, which are kept in green and red containers.

Some special substances are added to diesel to help it work better. One of these is ethylene-vinyl acetate (EVA), which stops waxy bits from forming and blocking fuel filters. Other helpers include antifoaming agents, antioxidants, and metal deactivating agents. These are added in very small amounts depending on how the diesel will be used and stored.

Standards

Diesel engines can use many different fuels, but special fuel called diesel fuel was created for high-performance engines in the 1930s. To make sure diesel fuel is safe and works well, rules called standards were made after World War II. These standards describe important qualities of the fuel, like how quickly it burns or its thickness.

Some of the main diesel fuel standards are:

Diesel fuel

• EN 590 (European Union)
• ASTM D975 (United States)
• GOST R 52368 (Russia; equivalent to EN 590)
• NATO F 54 (NATO; equivalent to EN 590)
• DIN 51601 (West Germany; obsolete)

Biodiesel fuel

• EN 14214 (European Union)
• ASTM D6751 (United States)
• CAN/CGSB-3.524 (Canada)

Measurements and pricing

Cetane number

Main article: Cetane number

The main way to check how good diesel fuel is to use is called the cetane number. This number tells us how quickly the fuel will start burning when it is sprayed into hot, squeezed air. A higher number means the fuel will catch fire more easily. In Europe, the normal diesel fuel for cars must have a cetane number of at least 51. Some special diesel fuels with extra cleaning and special mixes can have even higher numbers.

Fuel value and price

Further information: Gasoline and diesel usage and pricing

Diesel fuel is made mostly from carbon, about 86.1% of it. When it burns, it gives out energy, about 43.1 MJ for every kilogram. This is almost the same as petrol, which gives 43.2 MJ per kilogram. But because diesel is thicker, it holds more energy in the same space. In Europe, diesel fuel is between 0.820 to 0.845 kg for every litre. This is a bit more than petrol, which is between 0.720 to 0.775 kg for every litre. This difference is important when we compare prices.

Making diesel fuel from oil is usually easier than making petrol. But extra steps are needed to clean the diesel and take out sulfur, which can make it cost more. In many places, like the United States, United Kingdom, and Australia, diesel can cost more than petrol. This is because some factories that make diesel closed down, and more factories are making petrol instead. Also, a new kind of diesel called ultra-low-sulfur diesel is now used, and it needs special equipment to make.

In Sweden, there is a special type of diesel called MK-1. It has even less of some harmful chemicals and costs a little more to make. In Germany, taxes on diesel are lower than on petrol by about 28%.

Taxation

Diesel fuel is like the oil used to heat homes. In many countries, taxes on diesel used in cars are higher than on heating oil. To stop people from avoiding taxes, heating oil is often coloured or mixed with special chemicals. In some places, there is a special kind of diesel that is not taxed. This is used for things like farm machines or vehicles that do not drive on public roads. This diesel is coloured red so it is easy to spot if it is used in cars, which is not allowed and can lead to big fines. In the United Kingdom, Belgium, and the Netherlands, this coloured diesel is called red diesel. In the Republic of Ireland and Norway, it is coloured green. In India, taxes on diesel are lower than on petrol because many important things like grain are moved using diesel.

Taxes on a type of diesel called biodiesel change between states in the United States. Some states, like Texas, have no tax on biodiesel. Other states tax it the same as normal diesel but offer rewards to people who make or use biodiesel.

Uses

Diesel fuel is mainly used in high-speed diesel engines, especially in vehicles like cars and trucks. Not all diesel engines use diesel fuel—some big watercraft engines use heavier fuels instead. Some engines, like certain MAN M-System engines, can run on petrol.

Trucks and buses are now mostly powered by diesel engines, which need diesel fuel. Passenger cars usually use petrol, but in places like Europe and India, many cars use diesel fuel because it makes the engines more efficient.

Diesel fuel is also used in railroads, replacing older coal and fuel oil for trains. It’s not common in airplanes because diesel engines are heavier, but some old planes used diesel fuel because it was reliable and safer. In modern times, some diesel engines have been changed to work in airplanes.

Military vehicles often use diesel fuel because it’s safer and more efficient. Today, most tractors and heavy equipment use diesel fuel, which makes them work better and save fuel.

Diesel fuel has other uses too, like in special drilling fluids for oil and gas, and it was once used in some rocket engines in Germany during World War II.

Chemical analysis

In the United States, diesel fuel made from petroleum is made up of about 75% saturated hydrocarbons (like paraffins and cycloparaffins) and 25% aromatic hydrocarbons (such as naphthalenes and alkylbenzenes). The average chemical formula for common diesel fuel is C₁₂H₂₃, and it can range from C₁₀H₂₀ to C₁₅H₂₈.

Most diesel fuels can become hard in cold weather. Regular diesel fuel usually becomes hard around −8.1 °C (17.4 °F), while biodiesel can become hard between 2 °C and 15 °C (36 °F to 59 °F). As the temperature drops, diesel becomes thicker and can turn into a gel that does not flow well in fuel systems. Diesel fuel usually starts to catch fire safely at temperatures between 52 °C and 96 °C, making it safer than petrol but not suitable for engines that use sparks to start burning fuel.

Carbon dioxide formation

Diesel fuel is made of different molecules. When diesel burns, it creates carbon dioxide. This happens because the carbon in diesel mixes with oxygen from the air.

We can figure out how much carbon dioxide is made when diesel is burned. For every litre of diesel, about 2.63 kilograms of carbon dioxide is produced. For petrol, which is another type of fuel, about 2.3 kilograms of carbon dioxide is made for every litre burned.

Hazards

See also: Diesel exhaust

Environment hazards of sulfur

In the past, diesel fuel had more sulfur. Rules and taxes made oil refineries lower the amount of sulfur in diesel fuel. In the European Union, sulfur levels dropped a lot in the last 20 years. By the 1990s, diesel fuel could have up to 2000 parts per million of sulfur, but this dropped to 350 parts per million by 2000. By 2006, it was limited to 50 parts per million, called Ultra Low Sulfur Diesel (ULSD). By 2009, the limit in Europe was just 10 parts per million.

In the United States, stricter rules started in 2006 and became required by June 1, 2010 (see also diesel exhaust).

Algae, microbes, and water contamination

Main article: Microbial contamination of diesel fuel

There is often confusion about algae in diesel fuel. Algae need light to live, and since fuel tanks are closed, algae cannot survive. However, some microbes can live in diesel fuel.

These microbes form groups at the place where fuel meets water. They grow fast in warm temperatures and can even grow in cold weather if the fuel tank has heaters. Pieces of these groups can break off and block fuel lines and filters.

Water in fuel can damage the fuel injection pump. Some diesel fuel filters also catch water. Water in diesel fuel can freeze in the tank. When water freezes, it can block the fuel injector pump. Once water starts to freeze, the fuel can become thick and stop working until it warms up and becomes liquid again.

Road hazard

Diesel is not as flammable as petrol. But because it evaporates slowly, spills on the road can make vehicles slip. After the lighter parts evaporate, a greasy film stays on the road. This reduces tire grip and can make vehicles skid. The loss of grip is like driving on black ice, which can be very dangerous for two-wheeled vehicles, such as motorcycles and bicycles, especially in roundabouts.