Gas Oils Guide
Diesel Grades in ASTM D975-20
Historically, the quality of automotive fuels in the United States was specified by ASTM standards. Diesel fuels are covered by the ASTM D975 standard. Since 2004, the D975 standard has covered seven grades of diesel, Table 1. Heavier fuel oils Grade 5 and 6 (residual), which are used primarily for heating purposes, are described by ASTM D396.
| Grade | Description | Max Sulfur |
|---|---|---|
| No. 1-D S15 | A special-purpose, light middle distillate fuel for use in diesel engine applications with frequent and widely varying speeds and loads or when abnormally low operating temperatures are encountered. Higher volatility than that provided by No. 2-D fuels. | 15 ppm |
| No. 1-D S500 | 500 ppm | |
| No. 1-D S5000 | 5000 ppm | |
| No. 2-D S15 | A general-purpose, middle distillate fuel for use in diesel engines, especially in applications with relatively high loads and uniform speeds, or in diesel engines not requiring fuels having higher volatility or other properties specified in Grade No. 1-D fuels. | 15 ppm |
| No. 2-D S500 | 500 ppm | |
| No. 2-D S5000 | 5000 ppm | |
| No. 4-D | A heavy distillate fuel, or a blend of distillate and residual oil, for low- and medium-speed diesel engines in applications involving predominantly constant speed and load. |
The Sxxx designation was first adopted in the D975-04 edition of the standard to distinguish grades by sulfur content. The S5000 grades correspond to the “regular” sulfur grades, the previous No. 1-D and No. 2-D. S500 grades correspond to the previous “Low Sulfur” grades (D975-03). S15 grades are commonly referred to as “Ultra-Low Sulfur” grades or ULSD.
An ASTM standard (D2069) once existed for marine diesel fuels, but it has been withdrawn. It was technically equivalent to ISO 8217. While some marine diesel engines use No. 2 distillate, D2069 covered four kinds of marine distillate fuels: DMX, DMA, DMB, and DMC and residual fuels.
- DMX is a special light distillate intended mainly for use in emergency engines.
- DMA (also called marine gas oil, MGO) is a general purpose marine distillate that must be free from traces of residual fuel. DMX and DMA fuels are primarily used in Category 1 marine engines (< 5 liters per cylinder).
- DMB (marine diesel oil, MDO) is allowed to have traces of residual fuel, which can be high in sulfur. This contamination with residual fuel usually occurs in the distribution process, when using the same supply means (e.g., pipelines, supply vessels) that are used for residual fuel. DMB is produced when fuels such as DMA are brought on board the vessel in this manner. DMB is typically used for Category 2 (5-30 liters per cylinder) and Category 3 (≥ 30 liters per cylinder) engines.
- DMC is a grade that may contain residual fuel, and is often a residual fuel blend. It is similar to No. 4-D, and can be used in Category 2 and Category 3 marine diesel engines.
- Residual (non-distillate) fuels are designated by the prefix RM (e.g., RMA, RMB, etc.). These fuels are also identified by their nominal viscosity (e.g., RMA10, RMG35, etc.).
With the growing importance of alternative diesel fuels, standards have also been developed for biodiesel fuels and their blends.
Sulfur Content
Since the 1990’s, fuel quality has been increasingly more regulated by the US EPA under the authority of the Clean Air Act. In the context of the increasingly more stringent diesel emission standards, the most important fuel property regulated by the EPA became the sulfur content. Historically, the sulfur content in diesel fuels for highway and nonroad vehicles was limited to 0.5% (wt.) by ASTM specifications. The milestones in US environmental regulations limiting sulfur levels in diesel fuels can be summarized as follows:
- Highway Diesel Fuel
- 500 ppm: Sulfur limit of 500 ppm = 0.05% (wt.) became effective in October 1993. This fuel, commonly referred to as low sulfur diesel fuel, was introduced to facilitate sulfate particulate emission reductions, which were necessary for meeting the 1994 emission standards for heavy-duty highway engines.
- 15 ppm: Diesel fuel of maximum sulfur level of 15 ppm was available for highway use beginning in June 2006. This fuel, referred to as ultra low sulfur diesel (ULSD), was legislated by the EPA to enable catalyst-based emission control devices, such as diesel particulate filters and NOx adsorbers necessary for meeting the 2007-2010 emission standards for heavy-duty engines and the Tier 2 light-duty standards.
- Nonroad Diesel Fuel
The following sulfur requirements are applicable to Nonroad, Locomotive and Marine (NRLM) fuels, with the exception of heavy fuel oils (HFO) used in Category 2 and Category 3 marine diesel engines.- 500 ppm: Sulfur limit of 500 ppm became effective in June 2007 for nonroad, locomotive and marine fuels.
- 15 ppm: Sulfur limit of 15 ppm (ULSD) becomes effective in June 2010 for nonroad fuel, and in June 2012 for locomotive and marine fuels. ULSD has been legislated for nonroad engines to enable advanced emission control systems for meeting the Tier 4 nonroad emission standards.
- Category 3 Marine Engine Fuel
The United States and Canada applied to the IMO to establish an emission control area (ECA) along their shorelines. Once the ECA is established, it will trigger international and US EPA sulfur limits in marine fuels:- International IMO limits applicable in ECAs are 1% (10,000 ppm) sulfur beginning in 2010, and 0.1% (1,000 ppm) sulfur from 2015. SOx aftertreatment, such as SOx scrubbers, are allowed in lieu of low sulfur fuel.
- US EPA 2009 EPA Category 3 marine engine rule established a sulfur limit of 1,000 ppm for marine fuels produced and/or sold for use within an ECA. SOx aftertreatment can be used in lieu of low sulfur fuel. Additional flexibilities apply to vessels operated on the Great Lakes and Saint Lawrence Seaway: the low sulfur requirements can be deferred—subject to fuel availability and economic hardship provisions—and are not applicable to steamships.
In general, there are two primary grades of standard diesel fuel: Diesel #1 and Diesel #2. Diesel #2 is general purpose, being able to sustain heavy loads and providing better fuel economy. In fact, No. 2-D (when following ASTM D975-20 nomenclature) is specified by diesel automakers for normal driving conditions. #1 is more volatile and special-purpose, being used for cold conditions, for example. The two types of oil can be blended
According to ASTM D975-20: Standard Specification for Diesel Fuel Oils, there are seven diesel fuel grades:
- Grade No. 1-D S15
- Grade No. 1-D S500
- Grade No. 1-D S5000
- Grade No. 2-D S15
- Grade No. 2-D S500
- Grade No. 2-D S5000
- Grade No. 4-D Please
Note that three of these are variants of Diesel #1, and three are of Diesel #2. The distinction here is sulfur content, meaning that Grade No. 1-D S15 is a special-purpose, light middle distillate fuel at a maximum of 15 ppm sulfur. Grade No. 4-D includes more viscous middle distillates and blends with residual fuel oils.
1. Scope
1.1 This specification covers five grades of diesel fuel oils suitable for various types of diesel engines. These grades are described as follows:
1.1.1 Grade Low Sulfur No. 1-D—A special-purpose, light distillate fuel for automotive diesel engines requiring low sulfur fuel and requiring higher volatility than that provided by Grade Low Sulfur No. 2-D.
1.1.2 Grade Low Sulfur No. 2-D— A general-purpose, middle distillate fuel for automotive diesel engines requiring low sulfur fuel. It is also suitable for use in non-automotive applications, especially in conditions of varying speed and load.
1.1.3 Grade No. 1-D—A special-purpose, light distillate fuel for automotive diesel engines in applications requiring higher volatility than that provided by Grade No. 2-D fuels.
1.1.4 Grade No. 2-D—A general-purpose, middle distillate fuel for automotive diesel engines, which is also suitable for use in non-automotive applications, especially in conditions of frequently varying speed and load.
1.1.5 Grade No. 4-D—A heavy distillate fuel, or a blend of distillate and residual oil, for low- and medium-speed diesel engines in non-automotive applications involving predominantly constant speed and load.
Note 1—A more detailed description of the grades of diesel fuel oils is given in Appendix X1.2.
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1.2 This specification, unless otherwise provided by agreement between the purchaser and the supplier, prescribes the required properties of diesel fuels at the time and place of delivery.
1.2.1 Nothing in this specification shall preclude observance of federal, state, or local regulations which may be more restrictive.
Note 2—The generation and dissipation of static electricity can create problems in the handling of distillate diesel fuel oils. For more information on the subject, see Guide D 4865.
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1.3 Values are stated in SI units and are regarded as the standard.
2. Referenced Documents (purchase separately) 
ASTM Standards
D56 Test Method for Flash Point by Tag Closed Cup Tester
D86 Test Method for Distillation of Petroleum Products and Liquid Fuels at Atmospheric Pressure
D93 Test Methods for Flash Point by Pensky-Martens Closed Cup Tester
D129 Test Method for Sulfur in Petroleum Products (General High Pressure Decomposition Device Method)
D130 Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test
D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
D482 Test Method for Ash from Petroleum Products
D524 Test Method for Ramsbottom Carbon Residue of Petroleum Products
D613 Test Method for Cetane Number of Diesel Fuel Oil
D1266 Test Method for Sulfur in Petroleum Products (Lamp Method)
D1319 Test Method for Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator Adsorption
D1552 Test Method for Sulfur in Petroleum Products by High Temperature Combustion and Infrared (IR) Detection or Thermal Conductivity Detection (TCD)
D1796 Test Method for Water and Sediment in Fuel Oils by the Centrifuge Method (Laboratory Procedure)
D2274 Test Method for Oxidation Stability of Distillate Fuel Oil (Accelerated Method)
D2500 Test Method for Cloud Point of Petroleum Products and Liquid Fuels
D2622 Test Method for Sulfur in Petroleum Products by Wavelength Dispersive X-ray Fluorescence Spectrometry
D2624 Test Methods for Electrical Conductivity of Aviation and Distillate Fuels
D2709 Test Method for Water and Sediment in Middle Distillate Fuels by Centrifuge
D2880 Specification for Gas Turbine Fuel Oils
D2887 Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography
D3120 Test Method for Trace Quantities of Sulfur in Light Liquid Petroleum Hydrocarbons by Oxidative Microcoulometry
D3828 Test Methods for Flash Point by Small Scale Closed Cup Tester
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4176 Test Method for Free Water and Particulate Contamination in Distillate Fuels (Visual Inspection Procedures)
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4294 Test Method for Sulfur in Petroleum and Petroleum Products by Energy Dispersive X-ray Fluorescence Spectrometry
D4306 Practice for Aviation Fuel Sample Containers for Tests Affected by Trace Contamination
D4308 Test Method for Electrical Conductivity of Liquid Hydrocarbons by Precision Meter
D4539 Test Method for Filterability of Diesel Fuels by Low-Temperature Flow Test (LTFT)
D4737 Test Method for Calculated Cetane Index by Four Variable Equation
D4865 Guide for Generation and Dissipation of Static Electricity in Petroleum Fuel Systems
D5304 Test Method for Assessing Middle Distillate Fuel Storage Stability by Oxygen Overpressure
D5453 Test Method for Determination of Total Sulfur in Light Hydrocarbons, Spark Ignition Engine Fuel, Diesel Engine Fuel, and Engine Oil by Ultraviolet Fluorescence
D5771 Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Optical Detection Stepped Cooling Method)
D5772 Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Linear Cooling Rate Method)
D5773 Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Constant Cooling Rate Method)
D5842 Practice for Sampling and Handling of Fuels for Volatility Measurement
D5854 Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products
D6078 Test Method for Evaluating Lubricity of Diesel Fuels by the Scuffing Load Ball-on-Cylinder Lubricity Evaluator (SLBOCLE)
D6079 Test Method for Evaluating Lubricity of Diesel Fuels by the High-Frequency Reciprocating Rig (HFRR)
D6217 Test Method for Particulate Contamination in Middle Distillate Fuels by Laboratory Filtration
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration
D6371 Test Method for Cold Filter Plugging Point of Diesel and Heating Fuels
D6468 Test Method for High Temperature Stability of Middle Distillate Fuels
D6469 Guide for Microbial Contamination in Fuels and Fuel Systems
D6751 Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
D6890 Test Method for Determination of Ignition Delay and Derived Cetane Number (DCN) of Diesel Fuel Oils by Combustion in a Constant Volume Chamber
D6898 Test Method for Evaluating Diesel Fuel Lubricity by an Injection Pump Rig
D7039 Test Method for Sulfur in Gasoline, Diesel Fuel, Jet Fuel, Kerosine, Biodiesel, Biodiesel Blends, and Gasoline-Ethanol Blends by Monochromatic Wavelength Dispersive X-ray Fluorescence Spectrometry
D7042 Test Method for Dynamic Viscosity and Density of Liquids by Stabinger Viscometer (and the Calculation of Kinematic Viscosity)
D7094 Test Method for Flash Point by Modified Continuously Closed Cup (MCCCFP) Tester
D7220 Test Method for Sulfur in Automotive, Heating, and Jet Fuels by Monochromatic Energy Dispersive X-ray Fluorescence Spectrometry
D7344 Test Method for Distillation of Petroleum Products and Liquid Fuels at Atmospheric Pressure (Mini Method)
D7345 Test Method for Distillation of Petroleum Products and Liquid Fuels at Atmospheric Pressure (Micro Distillation Method)
D7371 Test Method for Determination of Biodiesel (Fatty Acid Methyl Esters) Content in Diesel Fuel Oil Using Mid Infrared Spectroscopy (FTIR-ATR-PLS Method)
D7467 Specification for Diesel Fuel Oil, Biodiesel Blend (B6 to B20)
D7545 Test Method for Oxidation Stability of Middle Distillate FuelsRapid Small Scale Oxidation Test (RSSOT)
D7619 Test Method for Sizing and Counting Particles in Light and Middle Distillate Fuels, by Automatic Particle Counter
D7668 Test Method for Determination of Derived Cetane Number (DCN) of Diesel Fuel OilsIgnition Delay and Combustion Delay Using a Constant Volume Combustion Chamber Method
D7683 Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Small Test Jar Method)
D7688 Test Method for Evaluating Lubricity of Diesel Fuels by the High-Frequency Reciprocating Rig (HFRR) by Visual Observation
D7689 Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Mini Method)
D7861 Test Method for Determination of Fatty Acid Methyl Esters (FAME) in Diesel Fuel by Linear Variable Filter (LVF) Array Based Mid-Infrared Spectroscopy
D7945 Test Method for Determination of Dynamic Viscosity and Derived Kinematic Viscosity of Liquids by Constant Pressure Viscometer
D8148 Test Method for Spectroscopic Determination of Haze in Fuels
D8183 Test Method for Determination of Indicated Cetane Number (ICN) of Diesel Fuel Oils using a Constant Volume Combustion ChamberReference Fuels Calibration Method
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E1064 Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
Keywords
Compression Ignition Engines – Diesel – Inorganic Matter Content – Liquid Fuels – Volatility
ICS Code
ICS Number Code 75.160.20 (Liquid fuels)
UNSPSC Code
UNSPSC Code 15101505(Diesel fuel)
More than twenty years after the adoption of the first WWFC_19_gasoline_diesel, some regions continue to have unacceptably high sulphur levels, even exceeding 10,000 ppm in some markets. To encourage these regions to bring their fuel quality in line with cleaner and more modern specifications, the WWFC Committee retained Category 1 as guidance for transitional diesel fuel quality. The Committee is also serving notice, however, that it intends to retire this category in a future edition.
- Category 1 – Markets with no or first-level requirements for emission control; based primarily on fundamental vehicle/ engine perfor- mance and protection of emission control systems. This category will be retired in a future edition.
- Category 2 – Markets with requirements for emission control, such as US Tier 1, US 1998 and 2004 Heavy-Duty On-Highway, Euro 2/II, Euro 3/III or equivalent emission standards, or other market demands.
- Category 3 – Markets with more stringent requirements for emission control, such as US LEV, California LEV or ULEV, US 1998 and 2004 Heavy-Duty On-Highway, Euro 4/IV, JP 2005 or equivalent emission standards, or other market demands.
- Category 4 – Markets with advanced requirements for emission control, such as US Tier 2, US Tier 3, California LEV II, US 2007/2010 Heavy-duty On-Highway, US Non-Road Tier 4, Euro 4/IV, Euro 5/V, EURO 6/6b, Euro VI, JP 2009 or equivalent emission standards, or other market demands. Category 4 fuels enable sophisticated NOx and particulate matter after-treatment technologies.
- Category 5 – Markets with highly advanced requirements for emission control (including GHG) and fuel efficiency, such as US Tier 3 Bin 5, US light-duty vehicle fuel economy, US Heavy-Duty Fuel Efficiency/GHG Emission, California LEV III and as amended, US 2007/2010 Heavy-duty On-Highway, US Non-Road Tier 4, Euro 6c, Euro 6dTEMP, Euro 6d, current EU CO2 targets, China 6a, China 6b or equivalent emission control and fuel efficiency standards, or other market demands. This category is intended to minimise real driving emissions (RDE) to levels required for Euro 6dTEMP (from 2017), Euro 6d (from 2020), Euro VI and China 6b (from 2023). Category 5 fuels enable sophisticated NOx and particulate matter after-treatment technologies.
- Diesel D2 Russian Gasoil L-0.2-62 Gost 305-82 – The GOST variant (Russia) for Gasoil is 305-82 specifying the sulphur content of 0.02% max, whereas in the U.S.A. ANSI has defined the US national standard for gasoil or DIN in Germany.
Diesel Fuel D2 & D6 – Standard diesel fuel (sometimes called diesel oil) comes in two grades: Diesel-1 (D1) and Diesel-2 (D2). Diesel or Diesel fuel in general is any fuel used in diesel engines. That’s why it’s also commonly called as AGO or Automotive Gas Oil. Diesel fuel is a type of fuel derived from the distillation of oil that is heavier than gasoline but lighter than engine oil and heavy oil. D1 is similar to kerosene and is lighter than D2. While D2 is sold most of the time, D1 is sold during winter in very cold climates and not sold in hot weather countries. But D2 is easily available in most countries around the world. Despite rising awareness of environmental protection, D2 remains to be a key type of fuel for use in vehicles in many countries. In particular, demand for D2 has risen significantly in Asia over the past years as a consequence of increasing number of cars. In view of the country sustained economic growth, D2 will continue to be undersupply in the China/India and market.
What Is Diesel EN590 ? – EN590 describes the physical properties that all automotive diesel fuel must meet if it is to be sold in the European Union and Britain. Automotive diesel has national variants but the usual variants traded are EN590 and EN560 which are specified by ISO in Paris. EN590 for diesel (in Europe) has been around for almost 20 years. However fuel, like most products, is subject to a process of continuous development – and that development includes responding to legislation. The EN590 standard has been amended many times since 1993. The EN 590 had been introduced along with the European emission standards. With each of its revisions the EN 590 had been adapted to lower the sulphur content of diesel fuel. Since 2007 this is called ultra low sulphur diesel as the former function of sulphur as a lubricant is absent (and needs to be replaced by additives). The quality of European diesel fuels is specified by the EN 590 standard. While these specifications not are mandatory, they are observed by all fuel suppliers in Europe. Automobile diesel EN 590 is intended for application in diesel engines. Diesel motor fuel quality meets the requirements of European Standard EN 590. For operation in the conditions of a temperate climate following marks of fuel diesel automobile EN 590 are offered: Grade C – limiting filterability temperature -5 ° C; Grade D – limiting filterability temperature -10 ° C; Grade E – limiting filterability temperature – 15 ° C; Grade F – limiting filterability temperature -20 ° C. The entire volume of produced diesel fuel quality meets the requirements for fuels for vehicles of Euro 4 and Euro 5. Low sulfur content in diesel EN 590 reduces emissions of sulfur oxides into the atmosphere, which is especially important for for inhabitants of big cities.
Some of the important revisions of the EN 590 standard have been:
- EN 590:1993 – the first EU diesel fuel specification. It established a sulphur limit of 0.2% in on-road and non-road diesel fuels.
- EN 590:1999 – this standard reflected the sulphur (350ppm) and cetane (51) specifications by Directive 98/70/EC.
- EN 590:2004 – Sulphur limits of 50ppm (Euro 4) and 10ppm (Euro 5) as regulated by Directive 2003/17/EC. FAME (Fatty Acid Methyl Ester) content of 5% (B5).
- EN 590:2009 – FAME content of 7% (B7) as regulated by Directive 2009/30/EC. This directive also adopts mandatory biofuel requirements for refiners and introduces a 10ppm sulphur limit in non-road fuels effective 2011.
What is Ultra Low Sulphur Diesel (ULSD) ?
Ultra Low Sulfur Diesel (ULSD) is diesel fuel with substantially lowered sulfur content. As of 2006, almost all of the petroleum-based diesel fuel available in Europe and North America is of a ULSD type.
There is not a single standard set of specifications and as the government mandated standard becomes progressively more strict so does the definition. The move to lower sulfur content is expected to allow the application of newer emissions control technologies that should substantially lower emissions of particulate matter from diesel engines.
This change occurred first in the European Union and is now happening in North America. New emissions standards, dependent on the cleaner fuel, have been in effect for automobiles in the United States since model year 2007.
ULSD has a lower energy content due to the heavy processing required to remove large amounts of sulfur from oil, leading to lower fuel economy. Using it requires more costly oil.
Diesel Fuel Oil D6
D6 is also be known as Residual Fuel Oil and is of high-viscosity. This particular fuel oil requires preheating to 220 – 260 Degrees Fahrenheit. D6 is mostly used for generators.
D6 is a type of residual fuel, mainly used in power plants and larger ships. The fuel requires to be preheated before it can be used. It is not possible to use it in smaller engines or vessels/vehicles where it is not possible to pre-heat it. D6 is its name in the USA. In other parts of the world it has other names.
Residual means the material remaining after the more valuable cuts of crude oil have boiled off. The residue may contain various undesirable impurities including 2 percent water and one-half percent mineral soil. D6 fuel is also known as residual fuel oil (RFO), by the Navy specification of Bunker C, or by the Pacific Specification of PS-400
Recent changes in fuel quality regulation now require further refining of the D6 in order to remove the sulfur, which leads to a higher cost. Despite this recent change, D6 is still less useful because of its viscosity as well as that it needs to be pre-heated before it can be used and contains high amounts of pollutants, such as sulfur. Since it requires pre-heating, it cannot be used in small ships or boats or cars. However large ships and power plants can use the residual fuel oil.
The price of D6 diesel traditionally rises during colder months as demand for heating oil rises, which is refined in much the same way.In many parts of the United States and throughout the United Kingdom and Australia, d6 diesel may be priced higher than petrol.
D6 Diesel Standards and Classification
CCAI and CII are two indexes which describe the ignition quality of residual fuel oil, and CCAI is especially often calculated for marine fuels.
Despite this marine fuels are still quoted on the international bunker markets with their maximum viscosity (which is set by the ISO 8217 standard – see below) due to the fact that marine engines are designed to use different viscosities of fuel.
The unit of viscosity used is the Centistoke and the d6 fuel most frequently quoted are listed below in order of cost, the least expensive first-
* IFO 380 – Intermediate d6 fuel oil with a maximum viscosity of 380 Centistokes
* IFO 180 – Intermediate d6 fuel oil with a maximum viscosity of 180 Centistokes
* LS 380 – Low-sulphur (<1.5%) intermediate d6 fuel oil with a maximum viscosity of 380 Centistokes
* LS 180 – Low-sulphur (<1.5%) intermediate d6 fuel oil with a maximum viscosity of 180 Centistokes
* MDO – Marine diesel oil.
* MGO – Marine gasoil.
Differences / Similarities Between Diesel, Fuel Oil, Bunker Oil.
The differences between diesel, fuel oil, and bunker fuel are hydrocarbons. Specifically, the difference is in the size and length of the hydrocarbons in each fuel. Hydrocarbons comprise the overwhelming majority of the components in fossil fuels — and in biofuels as well for that matter. Everything else in fossil fuels and biofuels is a contaminant. As the name implies, hydrocarbons consist of molecules with only two types of atoms: hydrogen and carbon.Hydrocarbons are the reason fossil fuels and biofuels have value. Hydrocarbons are the reason diesel, gasoline, fuel oil, natural gas, biodiesel, etc. ignite/combust/burn. And, it is because there are different hydrocarbon categories — and classes within those categories — that there are different fuels Diesel and fuel oil — including bunker fuel — are heavy fossil fuels. Gasoline is a medium weight of fossil fuel. The lightweight fossil fuels gas-state fuels like methane (natural gas) and propane.
Categories of Hydrocarbons: Understanding
The two categories of hydrocarbons are saturated and unsaturated. Saturated hydrocarbons are complete. They cannot take on additional hydrogen or carbon atoms. Unsaturated hydrocarbons are incomplete. They have room for the addition of hydrogen and carbon atoms. Because saturated hydrocarbons are complete, they are stable. Unsaturated hydrocarbons are incomplete and, therefore, unsaturated hydrocarbons are unstable and volatile. Lightweight fossil fuels — gas-state fuels — have high counts of unsaturated hydrocarbon. Heavy, stable fossil fuels like diesel, bunker fuel, and fuel oil have far fewer unsaturated hydrocarbons. Gasoline is a medium weight fuel that falls somewhere in the middle.
Hydrocarbons in Heavy Fossil Fuels
Diesel and fuel oil have, essentially, the same hydrocarbon makeup. Both are composed primarily of saturated hydrocarbons. “Petroleum-derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes).[53] The average chemical formula for common diesel fuel is C12H24, ranging approximately from C10H20 to C15H28.”
Classes of Hydrocarbons Within the Saturated and Unsaturated Categories
Saturated versus unsaturated hydrocarbons is one difference between light and heavy fossil fuels. But, there are also differences between fossil fuels because of the difference between hydrocarbons in those two categories. There is a total of four classes of hydrocarbons: paraffins, naphthenes, aromatics, and olefins.
Paraffins and naphthenes are the two classes of saturated hydrocarbons. Aromatics and olefins are the two classes of unsaturated hydrocarbons.
Paraffines A.K.A., Alkanes
Paraffins are also known as alkanes. Alkanes are single-chain hydrocarbons. The backbone of an alkane consists of carbon atoms. Alkanes are one of the two saturated hydrocarbon classes. The other class of saturated hydrocarbons is cycloalkanes, a.k.a., “naphthenes.”
The difference between paraffins and naphthenes is that naphthenes have branches. And sometimes naphthenes loop. Naphthene carbon atoms often have more than just the two carbon atom bonds along the spine of the molecule. The carbon atoms in a naphthene can have two, three, four or five bonds with other carbon atoms. And, the carbon atom on one end of the molecule chain’s spine bonds with the carbon atom on the other. A notable trait of naphthenes is that they are the most energy dense hydrocarbon class in either category of hydrocarbons.
Unsaturated Hydrocarbons
The two classes of unsaturated hydrocarbons are aromatics and olefins. Aromatics occur naturally in crude oil. Olefins are a byproduct of crude oil refinement and do not occur naturally in crude oil. Unstable and volatile, aromatics and olefins produce the most toxic emissions. Additionally, aromatics and olefins also produce emissions with the greenhouse gases with the greatest global warming potential.
Another difference between light and heavy fossil fuels is the size of the hydrocarbons they contain. The molecules and molecule chains in light fossil fuels are short and small. Those in heavy fossil fuels are long and large.
Hydrocarbon Molecule and Molecule Chain Sizes
Lightweight fossil fuels, as one might expect, consist of smaller molecules and molecule chains than heavy fossil fuels. And, again, unsaturated hydrocarbons comprise a larger portion of the hydrocarbons in light fuels. Heavy fossil fuels have a greater percentage of saturated, large and long hydrocarbon molecule chains.
The larger and longer the hydrocarbon molecule chains in a fuel, the greater the density of the fuel. However, the longer and larger the hydrocarbon molecule chains in a fossil fuel, the more difficult achieving combustion efficiency is. So, while there is more energy in heavy, dense fossil fuels, the more energy is wasted. The problem with diesel, fuel oil, and bunker fuel is that a high percentage of their hydrocarbons go unburned.
Achieving the same combustion efficiency typical of lightweight fuels when combusting heavy fuels requires higher heat and more advanced technologies. The combustion efficiencies of diesel, fuel oil and bunker fuel are one of the biggest differences. And, combustion efficiency is a property of the hydrocarbons.
The biggest difference between diesel and fuel oil are the hydrocarbon sizes within each, not the hydrocarbon classes.
Diesel: Hydrocarbon Types, Sulfur Content, and Cetane Rating
Unlike the hydrocarbons in gasoline vs diesel, the hydrocarbons in diesel and fuel oil are very similar. In fact, they are almost the same in several cases. The hydrocarbon makes up of diesel fuels, “are approximately similar to fuel oils used for heating (fuel oils no. 1, no. 2, and no. 4),” according to the U.S. Health and Human Services Department. Diesel and fuel oils consist of mixtures of aliphatic and aromatic hydrocarbons. “The aliphatic alkanes (paraffins) and cycloalkanes (naphthenes) are hydrogen saturated and comprise approximately 80-90% of the fuel oils. Aromatics (e.g., benzene) and olefins (e.g., styrene and indene) compose 10-20% and l%, respectively, of the fuel oils.”
The hydrocarbon makeup of diesel and fuel oils is very similar. But still, there are different types of diesel. The differences in diesel grades are dependent on two things. The number of contaminants — sulfur specifically — is one difference between fuel grades. The cetane level of different grades is the second.
Regular Diesel Vs Low-Sulfur
Sulfur is the contaminant in diesel that generates the most concern for those worried about the environmental and health effects of diesel emissions. Sulfur is not toxic nor a major pollutant in its natural state. But, when sulfur oxidizes to create sulfur oxides, the molecules become dangerous for both the environment and for the health of people, flora, and fauna.
Sulfur oxides are one of the two contributors from diesel fuel emission responsible for producing to acid rain. The U.S. Environmental Protection Agency explains, “Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents. The SO2 and NOX react with water, oxygen and other chemicals to form sulfuric and nitric acids. These then mix with water and other materials before falling to the ground. While a small portion of the SO2 and NOX that cause acid rain is from natural sources such as volcanoes, most of it comes from the burning of fossil fuels.”
It is because of acid rain that emissions governing bodies from around the world have, together, mandate the use of low-sulfur diesel in most commercial and passenger vehicles.
With respect to sulfur content, there is a significant difference between regular sulfur and low-sulfur. The U.S. Department of Energy explains, “ULSD is a cleaner-burning diesel fuel that contains 97% less sulfur than low-sulfur diesel (LSD). ULSD was developed to allow the use of improved pollution control devices that reduce diesel emissions more effectively but can be damaged by sulfur.”
Low Vs High Cetane Diesel
The cetane rating of diesel is analogous to the octane rating of gasoline, but the opposite. Octane additives increase the compression combustion resistance of gasoline. Cetane additives reduce the compression combustion resistance of a fuel. Both cetane and octane are measures of how much pressure a fuel can withstand before autoignition. Straight-run gasoline — gasoline without octane additives — is often weak to pressure and requires greater resistance.
Straight-run diesel, on the other hand, is often too resistant. That means a diesel engine with straight-run diesel will not start in cold weather, low-temperature conditions. Increasing the octane rating and weakening diesel’s pressure resistance allows engines to fire in the cold more easily.
The cetane rating of diesel is simply a measure of the API gravity of diesel, the weight. “A low-density fuel contains fewer BTUs and consequently provides less power to a diesel engine. A typical gravity for #2 diesel fuel is in the 32-34 range compared to a high-cetane fuel which typically has a gravity rating in the 36-38 range and more closely resembles a #1 diesel fuel,” explains GrowMark Incorporated.
While the hydrocarbons in diesel and several types of fuel oils are minimal, there is a rather large difference between those found in diesel and other types of fuel oils, bunk fuel particularly.
Fuel Oils: Types and Classes, Including Bunker Fuels
During the crude oil distillation process, light, medium, and heavy hydrocarbons separate, a.k.a., “fractionalize.” As the temperature of the oil inside a crude oil distillation column increases, hydrocarbons vaporize. The light hydrocarbons vaporize at lower temperatures that heavy hydrocarbons. Once vaporized, the hydrocarbons are drawn into storage tanks.
The vaporized distillates separate into gas, naphtha, kerosene, light diesel, and heavy diesel (distillate fuel oil).
But, there are also hydrocarbons in diesel that are so heavy, they will not vaporize. Instead, if the temperature gets too high, they will auto-ignite. The hydrocarbons that will not distill are residuals. From residuals come residual fuel oil. Since there are both distillate fuel oils and residual fuel oils, clearly, not all fuel oil is the same.
Classes of Fuel Oils
The two types of fuel oils divide into any number of classes. In the United States and North America, there are six classes in total: Number 1 through Number 6 fuel oil. The United Kingdom breaks down fuel oils into eight classes, four distillate and four residual.
There are two characteristics that separate the different classes of fuel oil. The first is the minimum flash point. The second difference between fuel oils is the minimum and maximum kinematic viscosity.
Flash Point of Different Classes of Fuel Oils
Flashpoint is the temperature at which an organic compound — fuel oil in this case — emits enough vapors to ignite in air. For example, Number 1 fuel oil has a flash point of around 109 degrees Fahrenheit. Number 6 fuel oil has a flash point around 150 degrees Fahrenheit.
Flashpoint plays a role in combustion traits of a fuel. Flashpoint is an indicator of the compression resistance of a fossil fuel. The compression of a gas generates heat. Exposed to enough heat, and fossil fuels auto-ignite. The higher the flashpoint of a fuel, the more pressure it can sustain before auto-igniting.
Another difference between fuel oils is their kinematic viscosities.
Kinematic Viscosity of Fuel Oil Classes
Kinematic viscosity is a measure of the fluidity of a fuel. CSC Scientific Company’s Amanda Ranowski explains, “Kinematic viscosity is the measure of a fluid’s inherent resistance to flow when no external force, except gravity, is acting on it.” Kinematic viscosity is a symptom of fuel density. And, fuel density is a measure of how much energy is in a fuel on a volume scale.
But, while high fuel density is generally thought of as a positive attribute, the high kinematic viscosity is often negative. Because fuels with high kinematic viscosity do not flow quickly, it is difficult to use them in combustion engines. Ideal fuels for combustion engines have high density and low kinematic viscosity.
Bunker fuel has the highest kinematic viscosity of all fuel oils and the highest flashpoint.
Essential Difference Between Diesel Fuel, Fuel Oil, and Bunker Fuel
With respect to chemical makeup, the difference between diesel, fuel oil, and bunker fuel is hydrocarbon size. Of the three, diesel contains the smallest, shortest hydrocarbon chains. Bunker fuel has the longest, largest hydrocarbon molecule chains. No. 1 through 5 fuel oil falls in the middle.
The other differences between diesel, fuel oil, and bunker fuel are their flashpoints and their kinematic viscosities. The flashpoint and kinematic viscosity of diesel is the lowest of the three heavy fuels. Bunker fuel has the highest flashpoint and kinematic viscosity of the heavy fossil fuels.