Diesel fuel, or gas oil, is one of the types of fossil fuels that is widely used in diesel engines, heavy machinery, energy production systems, and transportation. This fuel is derived from the distillation of crude oil and is used in many industries and transportation systems due to its high efficiency, lower consumption compared to gasoline, and greater energy production.

What is Diesel Fuel?

Gas oil (Gasoline oil) is a relatively heavy product of crude oil, obtained through the distillation process after kerosene. This substance is produced in both atmospheric and vacuum distillation columns, and in many refinery units, such as cracking, hydrocracking, and coking units, significant amounts of gas oil are also produced along with gasoline by altering the structure of heavy oil cuts.

Gas oil is generally a colorless liquid, but to better identify and distinguish it from other liquids and products, its color tends to lean towards brown. This substance is a mixture of various hydrocarbons, and its molecular structure typically contains between 14 and 20 carbon atoms (and in some cases, up to 25 carbon atoms).

The primary use of gas oil is as fuel in diesel engines, heating installations, and some factories. Diesel engines have a higher compression ratio than gasoline engines, allowing them to produce more power. For this reason, this type of engine is primarily used in heavy vehicles that require fuel storage tanks.

Comprehensive Review of Diesel Fuel Specifications: Key to Understanding Diesel Engine Performance

Diesel fuel, as one of the main fuels used in diesel engines, has characteristics that vary depending on the type of crude oil extracted and its application in various industries. Below, we review the most important specifications of diesel fuel:

1. Density (Diesel Density)

Density is one of the essential characteristics of diesel fuel, representing its weight in comparison to other fuels. The density of diesel fuel typically ranges from 0.8 kg/l to 0.87 kg/l. An important feature to note is that with the increase in petroleum and aromatic hydrocarbons in diesel fuel, its density also increases. This characteristic allows diesel fuel to perform more efficiently as fuel for diesel engines.

2. Distillation

Distillation is another key aspect in reviewing diesel fuel. The initial distillation point of this fuel is at a temperature of 180°C, and the final point is around 370°C. Distillation characteristics of diesel fuel are crucial as they serve as a good criterion for evaluating its quality and performance. According to ASTM standards, the distillation percentages of diesel fuel at different temperatures are as follows:

• Less than 65% at 250°C
• More than 85% at 350°C
• More than 95% at 370°C

3. Viscosity of Diesel Fuel

One of the important features of diesel fuel is its relatively high viscosity, or stickiness, which has a significant impact on its performance. If the viscosity of diesel fuel is excessively high, it may cause a drop in pressure in the fuel pipes, pumps, and injectors, affecting its flow. This can lead to serious issues in the operation and use of the fuel.

From the examination of diesel fuel specifications, it is evident that if the viscosity of the fuel is too low, its quality diminishes and negatively affects the performance of diesel engines. In general, the standard viscosity value of diesel fuel should range from 12 to 40 centistokes to ensure optimal performance under various conditions.

Types of Diesel Fuel and Their Technical Characteristics

Diesel fuel comes in various types that can be chosen based on the specific needs of industries and applications:

1. Standard Diesel (EN590)

This type of diesel is the most common and is used in cars and heavy machinery. Its characteristics include low sulfur content (less than 10 ppm) and strict environmental regulations.

2. Low Sulfur Diesel

To reduce pollution and meet environmental standards, low sulfur diesel is produced, especially designed for developed and industrialized countries.

3. Special Diesel for Industrial Machinery

This type of fuel is usually produced due to the need for special properties such as higher power or better stability at different temperatures.

Applications of Diesel Fuel

Due to its specific characteristics, diesel fuel is used in various industries:

• Transportation: Diesel is used to power trucks, buses, trains, and ships. Diesel engines are ideal for heavy vehicles due to their higher efficiency and lower fuel consumption.
• Heavy Machinery and Agriculture: Diesel is used in various agricultural machinery, such as tractors, as well as in construction and mining equipment.
• Energy Production: Diesel fuel is used in power plants and electrical generators for electricity generation.

Advantages and Disadvantages of Diesel Fuel

Advantages:

• Higher Efficiency: Diesel fuel produces more energy than gasoline, and diesel engines generally have lower fuel consumption.
• Suitable for Heavy Engines: Diesel engines generate more power, making them suitable for industrial machinery and heavy transportation.
• Longer Engine Life: Diesel engines typically have a longer lifespan and generally require less maintenance.

Disadvantages:

• Pollution: One of the main drawbacks of diesel fuel is the emission of greenhouse gases and pollutants such as nitrogen dioxide (NO2) and particulate matter, which are problematic, especially in densely populated cities.
• Need for Special Filters: Diesel engines require diesel filters to reduce pollutants.

Standards and Certifications

Diesel fuel must be produced in accordance with international and regional standards to ensure its quality and safety. Some of the most important standards include:

• EN590: European standard for diesel fuel, which includes its technical specifications.
• ISO 9001: Quality certification for the diesel fuel production process.
• ASTM D975: American standard for diesel and similar fuels.

Cloud Point and Pour Point of Diesel

The cloud point refers to the first temperature at which solid crystals begin to form when diesel is cooled. The pour point is the temperature at which the first movement of the diesel fluid occurs after freezing. To ensure that diesel fuel is resistant and suitable for cold weather, it must maintain its fluidity at low temperatures and prevent crystallization.

The appropriate range for cloud point and pour point in diesel fuel is typically between 0°C to -10°C and -15°C to -30°C, respectively. The higher the content of petroleum and aromatic substances in the diesel, the better its pour and cloud points will perform, offering better performance at lower temperatures.

Sulfur Content in Diesel

The presence of sulfur and its compounds in diesel can cause issues such as corrosion of the diesel engine components and air pollution. According to international standards, the maximum allowable sulfur content in diesel should be less than 50 ppm. To reduce these compounds, it is essential that diesel undergoes thorough refining during its production process.

Cetane Number and Aniline Point

The cetane number is a measure used to assess the quality of diesel fuel. A higher cetane number indicates that combustion inside the cylinder will occur more quickly and efficiently.

The aniline point refers to the lowest temperature at which equal volumes of fuel and aniline form a homogeneous phase. An increase in the aniline point in diesel fuel indicates higher quality and a good diesel index.

To determine the aniline point, a specified volume of diesel fuel is poured into a container, and an equal volume of aniline is added. The temperature of the mixture is gradually increased and stirred until both substances merge into a homogeneous solution. The temperature at this stage is recorded as the fuel’s aniline point.

Diesel in Diesel Engines

The operating process of a diesel engine differs significantly from that of a gasoline engine. In a diesel engine, combustion of the fuel does not occur simultaneously with its injection into the cylinder. Instead, there is a delay between the injection of the fuel and its combustion, known as the “ignition delay period.” This period is influenced by factors such as the type of fuel, engine design, and combustion conditions.

In a diesel engine, the process is divided into four main stages:

1. Air Intake: In the first stage, fresh air is drawn into the cylinder.
2. Compression and Temperature Rise: In the second stage, the air is compressed within the cylinder, causing its temperature to rise, preparing the conditions for fuel injection.
3. Spontaneous Combustion: During this stage, fuel is injected into the cylinder, and due to the high pressure and temperature, it ignites spontaneously without the need for a spark plug. At this point, the cylinder starts to expand.
4. Exhaust Gases Expulsion: Finally, in the fourth stage, the combustion gases are expelled from the combustion chamber through the exhaust system.

For optimal diesel engine performance, the chemical composition of the diesel fuel and engine conditions must be designed in such a way that spontaneous combustion in the combustion chamber is possible. These features contribute to the higher efficiency and performance of a diesel engine compared to a gasoline engine.

Cetane Number in Diesel

The Cetane number of diesel, similar to the octane number of gasoline, is a critical parameter for assessing fuel quality. It is typically determined in a single-cylinder CFR (Cooperative Fuel Research) engine, which is specifically designed for diesel fuel combustion. The cetane number is related to the type of hydrocarbons present in the fuel, and in general, hydrocarbons with a high cetane number tend to have a low octane number.

The cetane number determines the quality of diesel fuel; the higher this number, the easier it is for the fuel to ignite spontaneously in the combustion chamber, reducing the ignition delay time. This results in faster combustion of the fuel.

Problems Associated with a Low Cetane Number

When the cetane number is low, it can cause difficulties starting the vehicle, especially in cold weather. The excessive delay in ignition causes fuel to accumulate in the combustion chamber, and eventually, a large amount of high-energy fuel is combusted. This can lead to knocking and undesirable noise in the diesel engine, affecting its performance.

Testing and Comparing Fuel Quality

By testing various fuel mixtures in the CFR engine, it has been established that normal cetane (C16H34) has a cetane number of 100, while alpha-methyl naphthalene has a cetane number of 0. Normal cetane has a high ignition quality due to its short ignition delay, while alpha-methyl naphthalene has a long delay period and very poor combustion in a diesel engine.

By definition, the cetane number of a diesel fuel sample is the volume percentage of normal cetane mixed with alpha-methyl naphthalene, provided the ignition quality of this mixture matches that of the fuel sample in question. Diesel fuel cetane numbers typically range from 45 to 55.

Export and Sales Tips for Diesel Fuel

For exporting diesel fuel, it is essential to comply with customs regulations and international standards. Some important points in the sale and export of diesel fuel include the following:

1. Transportation:
   • Diesel is typically transported via tankers or ships.
   • To prevent contamination and preserve quality, diesel must be stored and transported under specific conditions.
   • The transportation equipment must be leak-proof and resistant to various weather conditions.
2. Customs Regulations:
   • Exporting diesel fuel to different countries requires a thorough understanding of the specific customs regulations and laws of each country.
   • Many countries require special permits for fuel imports, which must be obtained and approved before shipment.
   • Additionally, exporting to some countries may require specific quality inspections and adherence to fuel standards.

The Future of Diesel Fuel and Market Trends

With the advancement of new technologies and environmental pressures, the future of diesel fuel is expected to undergo significant changes. Some of the trends in the diesel fuel market are:

• Growth of Cleaner Technologies: As environmental concerns grow, many countries are turning to cleaner fuels such as natural gas and electricity.
• Diesel Fuel’s Sustainability: Despite the shift toward cleaner fuels, diesel will remain one of the main fuels for transportation and heavy industries. It is still crucial for sectors such as road transportation, agriculture, and heavy equipment.

Therefore, despite the environmental pressures, the demand for diesel in certain sectors remains strong, and its future will be influenced by technological advancements and developments in alternative fuels.