Which fuel type is known as HFO?

Heavy Fuel Oil is the correct answer because it refers to a specific type of residual fuel oil that is commonly used in marine engines and industrial applications. It is characterized by its high viscosity and density, making it suitable for large ships and power plants that can handle its properties. HFO is produced during the refining process of crude oil and is the leftover product after lighter fuels have been distilled.

The alternative options do not correctly define HFO. High Flash Oil suggests a different type of fuel that ignites at higher temperatures, which is not relevant to the characteristics of HFO. Hydrolysis Fuel Oil does not correlate with established fuel classifications and is misleading. High-grade Fuel Oil might imply a more refined quality, which does not describe the properties or applications of Heavy Fuel Oil accurately. Therefore, the understanding of HFO as Heavy Fuel Oil is critical for recognizing its role in maritime operations and energy generation.