Ameer Randolph
Diesel fuel, also known as diesel oil, is a liquid fuel designed for diesel engines, which are a type of internal combustion engine. Rudolf Diesel first experimented with diesel fuel for his compression-ignition engine in the 1890s. The molecular weight of diesel fuel is a crucial aspect of its chemical composition and plays a significant role in its combustion characteristics and performance. Understanding the molecular weight of diesel fuel is essential for optimizing engine efficiency, emissions, and fuel standards.
Characteristics and Values of Diesel Fuel
| Characteristics | Values |
|---|---|
| Molecular weight | 150-250 g/mol |
| Average composition | C12.9H23.9 |
| Average molecular weight | 178.6 |
| Liquid molecular weight | 188 |
| Vapor molecular weight | 130 |
| Density | 0.85 kg/l |
| Energy release when burnt | 37.7-39.1 MJ/l |
| Ash content | 100 ppm (0.01% mass) |
| Ramsbottom carbon residue | 0.15-0.35% mass |
| Boiling range | 170-360 °C |
| Carbon content | 86 wt-% |
| Hydrogen content | 14 wt-% |
| Common colloquial names | DERV, distillate, gas oil, petrodiesel, biodiesel, white diesel |
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What You'll Learn
Diesel fuel's molecular weight range of 150-250 g/mol
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 fuel is a fractional distillate of petroleum fuel oil, although non-petroleum alternatives such as biodiesel are also available.
The molecular weight of diesel fuel varies, with a non-limited range of 150-250 g/mol. This is because diesel fuel consists of hundreds of different hydrocarbon molecules, mainly paraffins, aromatics, and naphthenes, with approximately 12-20 carbon atoms. The average composition is C12.9H23.9, with a molecular weight of 178.6.
The molecular weight of diesel fuel is higher than that of gasoline, which has a range of 60-150 g/mol. Gasoline also contains mainly alkanes (paraffins), alkenes (olefins), and aromatics, but with fewer carbon atoms, typically 4-12.
Diesel fuel has a higher density than gasoline, with a density of about 0.85 kg/l compared to 0.70-0.75 kg/l for gasoline. When burnt, diesel releases more energy per litre than gasoline, with a range of 37.7-39.1 MJ/l compared to 34.9 MJ/l for gasoline.
Ultra-low-sulfur diesel (ULSD) is a type of diesel fuel with substantially lowered sulfur content. As of 2016, almost all petroleum-based diesel fuel available in the UK, mainland Europe, and North America is ULSD.
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Diesel's composition of hydrocarbons
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel designed for use in diesel engines. Diesel engines are internal combustion engines that do not require a spark for fuel ignition. Instead, they rely on the compression of inlet air and the subsequent injection of fuel. This process, known as compression ignition or spontaneous ignition, is made possible by the unique composition of diesel fuel, which primarily consists of long-chain hydrocarbons.
Diesel fuel is derived from crude oil through fractional distillation, specifically targeting the distillation window between 200°C and 350°C. This process results in a complex mixture of hydrocarbons, primarily aliphatic and aromatic hydrocarbons. Aliphatic hydrocarbons, also known as saturated hydrocarbons or paraffins, make up about 75% of diesel fuel. The remaining 25% consists of aromatic hydrocarbons, including benzene, styrene, naphthalenes, and alkylbenzenes. The average chemical formula for common diesel fuel is C12H23, with a range of approximately C10H20 to C15H28.
The long-chain hydrocarbons in diesel fuel differentiate it from gasoline, which primarily contains short-chain hydrocarbons. These long chains contribute to the higher density of diesel fuel compared to gasoline. Diesel fuel typically contains hydrocarbons with 12 to 20 carbon atoms, resulting in a higher boiling point range of 170°C to 360°C. This is in contrast to gasoline, which usually has 4 to 12 carbon atoms and a lower boiling point range of 30°C to 210°C.
The molecular weight of diesel fuel reflects its complex hydrocarbon composition and varies based on specific sources and compositions. The non-limited diesel fuel molecular weight range is generally given as 150-250 g/mol. However, diesel fuel is often classified into different grades, and the molecular weight can vary within this range. Additionally, diesel fuel typically contains small percentages of other elements, such as sulfur, nitrogen, and oxygen, which can influence its overall molecular weight.
The composition of diesel fuel has been the subject of standardization efforts, particularly regarding the reduction of sulfur content. Ultra-low-sulfur diesel (ULSD) has been introduced in various regions, including the United States, Europe, the United Kingdom, mainland Europe, and North America. These standards aim to reduce emissions and improve air quality by limiting the sulfur content in diesel fuel.
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How diesel differs from gasoline
Diesel and gasoline are both fuels that use internal combustion to generate power. However, they differ in composition, combustion process, engine design, performance, and applications.
In terms of composition, diesel and gasoline have distinct chemical structures. Gasoline primarily consists of alkanes (paraffins), alkenes (olefins), and aromatics, with hydrocarbons typically containing 4-12 carbon atoms. On the other hand, diesel fuel is composed mainly of paraffins, aromatics, and naphthenes, with hydrocarbons usually containing 12-20 carbon atoms. This gives diesel a higher molecular weight, ranging from 150-250 g/mol compared to gasoline's range of 60-150 g/mol. Diesel is also a heavier distillate of crude oil, produced closer to lubricating oil, resulting in a thicker density than gasoline.
The combustion processes in diesel and gasoline engines differ significantly. Gasoline engines mix fuel with air, compress the mixture, and use a spark plug to ignite it. In contrast, diesel engines employ a compression-ignited injection system, where fuel is injected and ignited by compressed inlet air without the need for spark plugs. This compression-ignition process gives diesel engines higher compression ratios, contributing to their higher fuel efficiency.
Engine design also varies between diesel and gasoline power plants. Diesel engines are generally larger, with bigger cylinders, more robust pistons, and multiple gears. The use of heavy-duty materials in diesel engines contributes to their longer life expectancy, often reaching 250,000 to 300,000 miles or more before requiring major maintenance. Gasoline engines, on the other hand, typically start showing cylinder wear around the 120,000 to 150,000-mile mark.
Performance-wise, diesel engines have certain advantages over gasoline engines. Diesel engines are known for their high torque output, especially at low RPMs, making them ideal for applications requiring the movement of heavy loads. They also have better fuel efficiency, with a 20% increase in thermal efficiency compared to gasoline engines, resulting in improved fuel economy. Additionally, diesel engines are generally more durable and have a longer lifespan due to their robust construction and simpler design.
However, gasoline engines have their strengths as well. They tend to produce higher horsepower, making them preferable for lightweight vehicles that require more speed and agility. Gasoline, being more refined and thinner in density, burns faster and is more volatile, contributing to increased power output. Gasoline engines are also smoother and quieter, making them the choice for applications where comfort is a priority.
In terms of applications, diesel engines are widely used in industries such as construction, transportation, and agriculture, where durability, power, and fuel efficiency are crucial. They are commonly found in heavy trucks, marine engines, and military applications. Gasoline engines, on the other hand, are often used in passenger vehicles, where their higher RPM capability, smoother operation, and lower upfront cost are advantageous.
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Ultra-low-sulfur diesel
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel designed for diesel engines. Diesel engines are a type of internal combustion engine in which fuel ignition occurs without a spark due to the compression of inlet air and the injection of fuel.
The shift towards ULSD is largely driven by environmental concerns and regulatory actions aimed at reducing diesel fuel emissions. High levels of sulfur in diesel exhaust, especially from older engines, can cause health issues. By reducing sulfur content, advanced emissions control technologies can be employed, substantially lowering harmful emissions from diesel combustion. For example, nitrogen oxide and particulate matter emissions, which are suspected to be carcinogenic and contribute to respiratory and cardiovascular issues, can be reduced by 90% and 95% respectively with ULSD.
However, the process of reducing sulfur content in diesel fuel alters its lubricity and overall chemical composition. This results in decreased fuel economy and increased production costs. Additionally, lower fuel lubricity can lead to increased engine wear and higher maintenance costs.
Overall, while ULSD offers environmental and health benefits by reducing harmful emissions, it also presents economic challenges due to increased production and maintenance costs. The adoption of ULSD reflects a growing global emphasis on environmental sustainability and the need to balance economic considerations with ecological responsibilities.
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Diesel's ignition characteristics
Diesel fuel, also known as diesel oil, heavy oil, or simply diesel, is a liquid fuel designed for use in diesel engines. Diesel engines are internal combustion engines that use compression to ignite the fuel, rather than a spark. This means that diesel fuel needs good compression ignition characteristics.
Rudolf Diesel, the German engineer who invented the diesel engine in the late 1890s, described the compression required for his cycle in his 1895 US patent (#542846). He explained that pure atmospheric air is compressed to a degree that the highest pressure and temperature are obtained before ignition or combustion. This compression increases the air temperature inside the cylinder so that the atomised diesel fuel injected into the combustion chamber spontaneously ignites.
In diesel engines, fuel is injected into the engine cylinder near the end of the compression stroke. During a phase known as ignition delay, the fuel spray atomises into small droplets, vaporises, and mixes with air. As the piston moves closer to the top dead centre, the mixture reaches the fuel's ignition temperature, causing ignition. The vapour then causes an abrupt increase in pressure above the piston, creating the characteristic diesel knocking sound.
The cetane number is a measure of the tendency of diesel fuel to knock in a diesel engine. The scale is based on the ignition characteristics of two hydrocarbons: n-hexadecane (cetane) and 2,3,4,5,6,7,8-heptamethylnonane. Cetane has a short delay period during ignition and is assigned a cetane number of 100, while heptamethylnonane has a long delay period and is assigned a cetane number of 15.
Overall, the ignition characteristics of diesel fuel are crucial for its use in diesel engines, and the compression and ignition process is a key factor in the engine's operation.
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Frequently asked questions
The molecular weight of diesel fuel ranges from 150-250 g/mol. Diesel fuel consists of hundreds of different hydrocarbon molecules, with hydrocarbons containing approximately 12-20 carbon atoms.
The US EPA lists the liquid molecular weight of #2 Diesel fuel as 188.
The vapor molecular weight of #2 Diesel fuel is 130.
