The Evolution Of Diesel Fuel: Understanding The Basics

Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a combustible liquid used as fuel for diesel engines. It is a mixture of hydrocarbons obtained by distillation of crude oil, with a boiling point range of approximately 150–380 °C. Diesel engines are multifuel, meaning they can run on a wide range of fuels, but the development of high-performance, high-speed diesel engines for cars and lorries in the 1930s led to the creation of diesel fuel, a fuel specifically designed for such engines.

Diesel fuel sources

Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel used in diesel engines, which are a type of internal combustion engine. Diesel engines are unique because fuel ignition occurs without a spark as a result of the compression of inlet air and the injection of fuel.

The most common type of diesel fuel is a specific fractional distillate of petroleum fuel oil, which is produced by the fractional distillation of crude oil at a temperature between 200 and 350 °C at atmospheric pressure. This process results in a mixture of carbon chains that typically contain between 9 and 25 carbon atoms per molecule. This fraction is then subjected to hydrodesulfurization. However, "straight-run" diesel often has insufficient supply and quality, so other sources of diesel fuel are blended in. One major source is obtained by cracking heavier fractions using visbreaking and coking.

Diesel fuel can also be derived from non-petroleum sources, such as biodiesel, biomass-to-liquid (BTL), or gas-to-liquid (GTL) diesel. Biodiesel is derived from biomass materials and vegetable seed oil. In the United States, biomass-based diesel fuels are also commonly used and produced. In 2022, U.S. refineries produced about 1.75 billion barrels (73.46 billion gallons) of ultra-low-sulfur diesel (ULSD), a type of diesel with a substantially lowered sulfur content.

Historically, diesel engines were tested with various fuel sources, including crude oil, kerosene, lamp oil, petrol, ligroin, coal tar creosote, paraffin oil, gasoline, fuel oil, shale oil, and peanut oil. Diesel engines typically ran on cheap fuel oils, such as heavy fuel oils, which are still used in sea-going watercraft.

Diesel engine suitability

Diesel Exhaust Fluid (DEF) is a critical additive for diesel-powered vehicles and heavy equipment. DEF is a mix of deionized water and urea, which combines to convert harmful nitrogen oxide emissions from diesel engines into safe water and nitrogen. DEF is injected into the exhaust stream where it reacts with NOx in the presence of a catalyst to form harmless nitrogen and water vapour.

Almost every diesel-powered engine in the United States relies on DEF. DEF is consumed at a rate of about 50 to 1 with diesel, meaning for every 50 gallons of fuel burned, 1 gallon of DEF is consumed. However, this can vary depending on the vehicle, with some sources stating that DEF consumption can range from 1% to 3% of diesel fuel usage.

DEF is essential for reducing harmful emissions in diesel engines, helping them meet environmental standards and regulations. Without DEF, diesel vehicles would violate federal emissions standards, and the engines may not start. DEF also improves fuel efficiency by around 3% to 4%, resulting in reduced fuel costs and a lower carbon footprint.

DEF is available at select gas stations, but it may be more convenient for businesses with fleets of vehicles to utilise a dedicated fueling station that provides both diesel fuel and DEF. It is important to note that DEF should never be added to the diesel fuel tank, as this can result in costly repairs.

Diesel fuel standards

History of Diesel Fuel Standards

The first diesel fuel standards were introduced after World War II to meet the needs of emerging high-performance, high-speed diesel engines. Over time, as environmental concerns grew, the focus shifted towards reducing sulfur levels and harmful emissions from diesel fuel.

Standardization

Diesel fuel is standardized in many countries to maintain consistent quality. For example, the standard for diesel fuel in the European Union is EN 590, which replaced the previous DIN 51601 standard in 1993. This standard sets specifications for properties such as cetane number, density, flashpoint, and sulfur content.

Sulfur Content Regulations

Sulfur content in diesel fuel has been a major focus of diesel fuel standards due to its impact on emissions. The US Environmental Protection Agency (EPA) began regulating sulfur levels in diesel fuel in 1993. In 2006, the EPA implemented more stringent regulations, reducing the sulfur content to 15 parts per million (ppm), known as ultra-low sulfur diesel (ULSD). Similar reductions in sulfur content have been achieved in the European Union, with the Euro 5 standard allowing a maximum sulfur content of 10 ppm as of 2009.

EPA Diesel Fuel Standards in the United States

The EPA manages a comprehensive fuel compliance program in the United States, targeting all parties in the distribution system. EPA diesel fuel standards have evolved over time, with key milestones including:

• 2006: Phase-in of ULSD for on-road diesel, with a maximum sulfur level of 15 ppm.
• After 2010: Requirement for all highway diesel fuel and vehicles to use ULSD.
• 2014: Mandate for all nonroad, locomotive, and marine (NRLM) diesel fuel and engines to use ULSD, with some exceptions for older engines.

State-Level Regulations

In the United States, additional regulations can be imposed at the state level. For example, California has implemented its own stringent diesel fuel program, setting standards for aromatic hydrocarbons, sulfur, and lubricity. California's Low Carbon Fuel Standard (LCFS) also places unique requirements on the renewable content of diesel fuel.

ASTM Standards

The American Society for Testing and Materials (ASTM) develops industry standards for diesel fuel, such as the ASTM D975 standard. ASTM standards specify various technical parameters of automotive fuels and are recognized internationally.

Diesel fuel additives

For example, AR6500 Diesel Treatment by Archoil is a popular additive that improves lubricity, boosts cetane, and keeps the fuel system clean. It also helps to prevent carbon build-up in injectors, the turbo, and the Diesel Particulate Filter (DPF). This product is suitable for all diesel vehicles.

Hot Shot's Secret offers a range of diesel fuel additives, including Diesel Extreme, which is a fully formulated cleaner that removes harmful internal and external diesel injector deposits. It combines a cetane booster, a fuel stabilizer, and a water demulsifier additive to ensure the fuel system stays clean and operates efficiently. Another product by Hot Shot's Secret is the LX4 Lubricity Extreme, which is an ultra-low sulfur diesel fuel lubricity additive that helps prevent scarring and wear on essential engine components.

Opti-Lube XPD is another top-rated diesel fuel additive that enhances lubricity, boosts cetane, cleans injectors, and includes an anti-gel to keep fuel flowing down to -10°F. This additive is ideal for everyday use and is reported to improve fuel economy and reduce emissions.

Some additives are designed specifically for cold weather conditions, such as the Diesel Winter Anti-Gel by Hot Shot's Secret, which helps improve cold starts, prevent icing and gelling, and reduce fuel line freeze. Similarly, Power Service offers diesel additives for trouble-free winter operation.

While some users have reported noticeable improvements in engine performance and fuel mileage with the use of additives, others have not observed significant differences. It is important to note that, while additives may provide certain benefits, they are not always necessary for the proper operation of diesel engines.

Diesel fuel production

Diesel fuel is a mixture of hydrocarbons obtained by distillation of crude oil. It is a distillate fraction of crude oil, which is blended from several refinery streams, mostly from the primary distillation unit. The distillates heavier than kerosene derived by atmospheric distillation of crude oil are the gasoil streams, which are the main blending components for diesel fuel production. Additional types of gasoil can be derived from cracking processes.

The production of diesel fuel involves first distillation, then various conversion steps, and finally clean-up. In the primary refining unit, distillation takes place at atmospheric pressure, with the furnace temperature set to achieve maximum distillation without cracking. The quality and quantity of the streams drawn off depend on their boiling range and the crude oil used. Diesel fuels generally have a boiling range of 150 °C to 380 °C.

To meet market demands, refineries use conversion processes to break down large hydrocarbon molecules into smaller ones using heat, pressure, or catalysts. Thermal cracking (visbreaking and coking), catalytic cracking, and hydrocracking are employed to increase the yield of desired products. The final products are obtained by blending conversion products with the primary distillation streams.

Upgrading processes are also used to remove undesirable compounds, such as sulfur and nitrogen. The most common upgrading process is hydrotreating, which involves chemical reactions with hydrogen to saturate aromatic rings and remove impurities. Hydroprocessing can range from mild hydrofinishing to more severe hydrotreating, depending on the desired level of impurity removal.

Renewable diesel, also known as biodiesel, is an alternative to standard petroleum diesel. It is made from biomass, such as vegetable oil, agricultural waste, and trash. The production process starts with hydrogenation or hydrotreating to remove oxygen from the fuel, resulting in a clean, high-performance hydrocarbon molecule. Isomerization is then used to prevent freezing in cold weather, followed by fractionation to separate the product into a liquid state. Finally, the renewable diesel is distributed to businesses and consumers, sometimes blended with other fuels.

Frequently asked questions