D6 Diesel
AKA Virgin Fuel oil / residual fuel oil / bunker oil
D6 Diesel, also referred to as Residual Fuel Oil, Bunker Fuel Oil, or Bunker Oil, is a high-viscosity fuel primarily used for industrial and marine applications. This heavy fuel oil requires preheating to a temperature of 220–260°F before it can be utilized effectively. D6 is predominantly employed in power plants and large ships, where its high energy density makes it an efficient choice. However, its need for preheating limits its use to systems specifically designed for such operations. It is unsuitable for smaller engines, vehicles, or vessels that lack the capability to preheat the fuel. While commonly known as D6 Diesel in the United States, this fuel is recognized by different names in various parts of the world.
Understanding D6 Diesel (Residual Fuel Oil)
D6 Diesel, also called Residual Fuel Oil (RFO), Bunker C (as per Navy specifications), or PS-400 (Pacific Specification), refers to the material left after the more valuable components of crude oil are boiled off. This residual oil often contains impurities, including up to 2% water and 0.5% mineral soil.
Regulations and Refining
Recent regulations aimed at reducing sulfur content in fuels have necessitated additional refining of D6 Diesel, resulting in higher production costs. Despite these improvements, D6 remains less versatile due to its high viscosity, significant pollutant content, and requirement for preheating before use. These limitations make it unsuitable for small vessels, vehicles, or systems without specialized equipment. However, it is still widely used in large ships and power plants that can accommodate its specific handling requirements.
Market Dynamics
The price of D6 Diesel tends to increase during colder months due to higher demand for heating oil, which is processed similarly. In some regions, including parts of the United States, United Kingdom, and Australia, D6 Diesel may even surpass petrol prices during peak demand periods.
D6 Diesel Standards and Classification
The quality of D6 Diesel, particularly residual fuel oil, is evaluated using two key indexes:
-CCAI (Calculated Carbon Aromaticity Index): Commonly calculated for marine fuels to indicate ignition quality.
-CII (Combustion Index Indicator): Another measure of ignition properties.
While ignition quality is important, marine fuels are still primarily categorized by viscosity, which aligns with the ISO 8217 standard. This classification system reflects the operational design of marine engines, which accommodate various fuel viscosities.
Viscosity and Cost Classification
Viscosity, measured in Centistokes, is a critical factor in determining the type and cost of D6 Diesel. Below are common classifications of D6 fuels, listed from least to most expensive: IFO 380: Intermediate fuel oil with a maximum viscosity of 380 Centistokes. IFO 180: Intermediate fuel oil with a maximum viscosity of 180 Centistokes. LS 380: Low-sulfur (<1.5%) fuel oil with a maximum viscosity of 380 Centistokes. LS 180: Low-sulfur (<1.5%) fuel oil with a maximum viscosity of 180 Centistokes. MDO (Marine Diesel Oil): A more refined, lower-viscosity diesel fuel. MGO (Marine Gasoil): A highly refined, low-sulfur gasoil used in marine engines.