Rajan Wilcox
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel designed for diesel engines, which are multifuel and can run on a wide range of fuels. Diesel fuel is typically standardised, with properties such as cetane number, density, flash point, sulphur content, and biodiesel content being defined. The density of diesel fuel is about 0.820 to 0.85 kg/l, which is higher than that of gasoline, and it vaporises at temperatures between 149°C and 371°C. The vapor pressure of diesel fuel affects its fire point, which is the temperature at which the flame can be sustained by vapours. This article will explore the vapor density of diesel fuel, its impact on engine performance, and how it compares to other fuels.
Characteristics and Values of Diesel Fuel
| Characteristics | Values |
|---|---|
| Composition | Mixture of hydrocarbons obtained by distillation of crude oil |
| Crude Oil Type | Thin, low-density ("high-gravity") to thick, high-density ("low-gravity") crude oils |
| Conversion Process | Catalytic cracking and hydrocracking ("cracking" of large molecules into smaller ones) |
| Upgrading Process | Hydrotreating (removes undesirable trace compounds) |
| Heat Value | Number 2: 139,500 BTUs/gallon; Number 1: 125,500 BTUs/gallon |
| Cetane Rating | Minimum: 40; Maximum (without causing fuel knocking): 48 |
| Viscosity | Measured at 40 °C; increases as temperature decreases |
| Sulphur Content | Ultra-low-sulfur diesel (ULSD) widely available since 2016 |
| Water Content | High levels can cause internal rusting of fuel systems |
| Standard | EN 590 (European Union); varies by country |
| Classes | 1D, 2D, 4D (vary by viscosity and boiling point ranges) |
| Freezing Point | Petrodiesel: -8.1 °C; Biodiesel: 2 to 15 °C |
| Vaporisation Temperature | 149-371 °C |
| Flash Point | 52-96 °C |
| Density | 0.820-0.845 kg/L at 15 °C |
| Carbon Content | Approximately 86.1% of fuel mass |
| CO2 Emissions | 73.25 g/MJ |
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What You'll Learn
Diesel fuel classes
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is any liquid fuel designed for use in a diesel engine. The diesel engine is a multifuel engine that can run on a wide range of fuels. However, the development of high-performance, high-speed diesel engines for cars and lorries in the 1930s led to the need for a specific type of fuel known as diesel fuel.
Diesel fuel is typically standardised to ensure consistent quality. The first standards were introduced after World War II. The standard definitions include properties such as cetane number, density, flashpoint, sulphur content, and biodiesel content. The principal measure of diesel fuel quality is its cetane number, which indicates how readily the fuel ignites when sprayed into hot compressed air.
In the United States, diesel fuels are classified into three categories: 1D, 2D, and 4D. These classes are distinguished by their viscosity and boiling point ranges. 4D fuels are typically used in low-speed engines, while 2D fuels are suitable for warmer weather and are sometimes mixed with 1D fuel for winter use. 1D fuel is preferred in cold weather due to its lower viscosity.
In the European Union, the standard for diesel fuel is EN 590. The density of EN 590 diesel fuel is defined as 0.820 to 0.845 kg/L at 15 °C. This standard also applies in the United Kingdom and Australia, where diesel fuel may be priced higher than petrol per gallon or litre.
Diesel fuel has several colloquial names and variations depending on the region. In Australia, it is known as distillate, while in Indonesia, Israel, and the Middle East, it is commonly referred to as Solar. In the United Kingdom, diesel fuel for road use is often called white diesel, and in the United States, it is sometimes called diesel-engine road vehicle (DERV).
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Vapor pressure and fire point
Diesel fuel, also known as diesel oil or heavy oil, is a liquid fuel designed for diesel engines, which are internal combustion engines that use fuel ignition without a spark. Diesel engines are multifuel and can run on a wide range of fuels. However, the development of high-performance, high-speed diesel engines for cars and lorries in the 1930s led to the need for a specific type of diesel fuel.
Diesel fuel is standardised to ensure consistent quality, with the first standards introduced after World War II. The standard measures specific properties, including cetane number, density, flash point, sulphur content, and biodiesel content. The principal measure of diesel fuel quality is its cetane number, which indicates how readily the fuel ignites when sprayed into hot compressed air. The higher the cetane number, the more easily the fuel ignites. For example, European road diesel (EN 590 standard) has a minimum cetane number of 51.
The density of diesel fuel is approximately 0.820 to 0.845 kg/L at 15 °C (59 °F). This density is about 9.0-13.9% higher than that of gasoline (petrol), which has a density of 0.720-0.775 kg/L at the same temperature. Due to its higher density, diesel fuel offers a greater volumetric energy density, providing a higher net heating value per unit mass than gasoline.
The flash point of diesel fuel, which is the temperature at which it ignites, varies between 52 and 96 °C. This is significantly higher than the flash point of gasoline, making diesel safer to use and unsuitable for spark-ignition engines. The higher flash point of diesel fuel is not related to its performance or auto-ignition qualities. Diesel fuel typically freezes at temperatures around −8.1 °C (17.4 °F), and its viscosity increases noticeably as the temperature decreases, turning it into a gel that cannot flow in fuel systems at temperatures between −19 to −15 °C (−2 to 5 °F).
While I could not find specific information on the vapor pressure of diesel fuel, I did find that diesel fuel number 1 is essentially kerosene, which has a true vapor pressure of 0.0041 psia at 40 °F, 0.0085 psia at 60 °F, 0.015 psia at 80 °F, and 0.029 psia at 100 °F, according to the U.S. EPA. Vapor pressure is important in fuel systems as it can affect the available NPSH (Net Positive Suction Head) for pumps.
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Cetane number
The CN is calculated by blending cetane and isocetane to determine the same ignition delay. Cetane has a cetane number of 100, while isocetane's measured cetane number is 15. Once the blend is known, the CN is calculated as a volume-weighted average, rounded to the nearest whole number. The cetane number scale is based on the ignition characteristics of these two hydrocarbons.
The CN is an important factor in determining the quality of diesel fuel, but it is not the only one. Other measurements of diesel fuel quality include energy content, density, lubricity, cold-flow properties, and sulfur content. The cetane number of diesel fuel hydrocarbons varies with the hydrocarbon types present. Normal paraffins have high cetane numbers that increase with carbon number, while molecules with many short side chains have low cetane numbers. Aromatics have cetane numbers ranging from zero to 60.
The cetane number is also an indicator of the combustion speed of diesel fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. Fuels with lower cetane numbers have longer ignition delays, requiring more time for the fuel combustion process to be completed. Therefore, high-performance diesel engines require fuel with a higher cetane rating. Generally, diesel engines operate well with a CN from 40 to 55, and premium diesel fuel can have a cetane number as high as 60.
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Diesel fuel standards
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel specifically designed for diesel engines. Diesel engines are multifuel, meaning they can run on a wide range of fuels. However, the development of high-performance, high-speed diesel engines for cars and lorries in the 1930s led to the need for a specific type of fuel: diesel fuel.
Diesel fuel is typically classified into three types in the USA: 1D, 2D, and 4D. The difference between these classes depends on viscosity and boiling point ranges. 4D fuels are generally used in low-speed engines, while 2D fuels are used in warmer weather and are sometimes mixed with 1D fuel for winter. 1D fuel is preferred in cold weather due to its lower viscosity.
In terms of environmental impact, diesel fuel regulations have been implemented to reduce harmful emissions. For example, the US EPA has been regulating sulfur levels in diesel fuel since 1993, and in 2006, they began phasing in more stringent regulations to lower sulfur content to 15 parts per million (ppm), known as ultra-low sulfur diesel (ULSD). These regulations have resulted in significant health and environmental benefits, reducing harmful emissions from on-road and non-road diesel sources by more than 90%. Similarly, the California Diesel Fuel program has set stringent standards for diesel fuel specifications, resulting in cost-effective emission reductions from diesel-powered vehicles.
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Diesel fuel composition
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel designed for use in diesel engines. These engines are multifuel, meaning they can run on a wide range of fuels, including gasoline, alcohol, kerosene, and fuel oil. However, the development of high-performance, high-speed diesel engines in the 1930s led to the creation of a specific type of diesel fuel. This fuel is standardised to ensure consistent quality and defined by certain properties such as cetane number, density, flash point, sulphur content, and biodiesel content.
The most common type of diesel fuel is a specific fractional distillate of petroleum fuel oil, derived from crude oil through fractional distillation. It consists mainly of aliphatic and aromatic hydrocarbons with a boiling point range of approximately 163–357 °C. Diesel fuel contains more non-volatile components than gasoline and has a higher boiling range, typically between 160 °C and 371 °C. Due to this higher boiling range, diesel fuel must be sprayed and cannot be evaporated in the air without risking pre-ignition. Diesel fuel also has a higher density than gasoline, with the density of EN 590 diesel fuel defined as 0.820 to 0.845 kg/L at 15 °C. This higher density results in a higher volumetric energy density, providing a net heating value of 43.1 MJ/kg compared to 43.2 MJ/kg for gasoline.
In addition to petroleum-derived diesel, also known as petrodiesel, alternative types of diesel fuel that are not derived from petroleum are being developed and adopted. These include biodiesel, biomass-to-liquid (BTL), and gas-to-liquid (GTL) diesel. Biodiesel, for example, is derived from biological sources such as vegetable oils or animal fats and can be used in blends with petrodiesel or as pure biodiesel (B100). It has a higher oxygen content than petrodiesel, reducing the emissions of certain pollutants and improving ignition characteristics. Biodiesel typically freezes at higher temperatures than petrodiesel, ranging from 2 to 15 °C.
To improve the performance of diesel fuel in cold weather, additives such as ethylene-vinyl acetate (EVA) are used as "cold flow improvers". EVA inhibits the crystallisation of waxes that can block fuel filters. Other additives used in diesel fuel include antifoaming agents (silicones), antioxidants (hindered phenols), and "metal deactivating agents" (salicylaldimines). These additives are used to enhance the storage and performance characteristics of diesel fuel.
In summary, diesel fuel composition varies depending on the specific type of diesel fuel, but it is primarily derived from fractional distillation of crude oil, resulting in a mixture of hydrocarbons with a high boiling range and density. Standardisation of diesel fuel ensures consistent quality, and additives are used to enhance its performance and storage characteristics.
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Frequently asked questions
Diesel fuel, also known as diesel oil, is any liquid fuel designed for use in a diesel engine. The density of diesel fuel varies depending on the specific fuel type and its temperature. For example, the density of EN 590 diesel fuel is defined as 0.820 to 0.845 kg/L at 15 °C (59 °F).
The density of diesel fuel is influenced by factors such as viscosity, boiling point ranges, and temperature. Diesel fuels are classified into 1D, 2D, and 4D variants, with different viscosity and boiling point characteristics. The density of diesel fuel also varies with temperature, increasing as the temperature decreases.
The density of diesel fuel is higher than that of gasoline (petrol). The density of petroleum diesel is approximately 0.85 kg/l, which is about 15-20% higher than the density of gasoline, typically ranging from 0.70-0.75 kg/l.
