Aviation fuel is chemically derived from the same distillation fraction of crude oil as common kerosene, but the aviation product is an intensely refined and highly specified substance. The fuels that power commercial airliners are not interchangeable with the kerosene used for home heating or lamps. This distinction is based on the extreme performance requirements and safety standards necessary for flight operations at high altitudes and varying temperatures.
Kerosene is the Base, But Not the Final Product
Aviation turbine fuel, commonly called jet fuel, originates from the kerosene fraction during the crude oil refining process. This fraction is composed of hydrocarbons with carbon chains ranging from 8 to 16 atoms in length, giving it a density higher than gasoline but lower than diesel fuel. Jet fuel is fundamentally a highly purified and modified version of kerosene.
Commercial or home-use kerosene (K-1) is not subjected to the same rigorous purification and quality control standards as aviation fuel. Aviation fuel undergoes extensive processing to remove impurities, such as sulfur compounds and water. This removal is necessary because impurities could degrade engine components or freeze at high altitudes, ensuring consistency in energy density and combustion characteristics for turbine engine performance.
The Two Major Fuel Categories in Aviation
Aviation fuels are separated into two categories based on the engine type they power: turbine-engine fuels and piston-engine fuels. Jet fuel is the kerosene-based fuel used for jet engines and turboprop engines, which utilize a continuous combustion process. It is the dominant fuel in commercial and military aviation due to the widespread use of turbine technology.
The second category is Aviation Gasoline (Avgas), which is used exclusively in aircraft with reciprocating piston engines, typically found in smaller, general aviation planes. Avgas is chemically similar to automotive gasoline, being light and highly volatile, and contains a high octane rating to prevent engine knocking. Crucially, Avgas is a form of specialized gasoline, while jet fuel is kerosene-based.
Defining the Grades of Aviation Kerosene
The most common grades of aviation kerosene are Jet A and Jet A-1, differentiated primarily by their freezing points. Jet A, primarily used in the United States, has a maximum freezing point of -40°C (-40°F). Jet A-1 is the global standard, requiring a maximum freezing point of -47°C (-53°F), which makes it suitable for long-haul international flights encountering colder high-altitude temperatures.
Jet fuels also contain specific additives to maintain performance and safety in flight. These additives include:
- Anti-icing agents, which prevent water dissolved in the fuel from freezing and potentially clogging filters.
- Anti-static additives, which safely dissipate static electricity that can build up during high-speed pumping, reducing fire hazards.
- Corrosion inhibitors, which protect the integrity of the aircraft’s fuel system.
- Metal deactivators, which are added in trace amounts for system protection.
Critical Handling and Safety Requirements
Aviation kerosene is subject to rigorous quality control (QC) procedures that are far beyond those for ground-based fuels. This testing ensures the fuel meets the precise chemical and physical specifications necessary for safe flight. The presence of water or sediment is actively monitored, as these contaminants can cause engine malfunctions or promote microbial growth within the fuel tanks.
Another important safety measure is the flash point, which is the lowest temperature at which the liquid gives off enough vapor to form an ignitable mixture with air. Jet fuel has a relatively high flash point of at least 38°C (100°F), classifying it as a combustible liquid rather than a highly flammable one like gasoline. This higher flash point makes it safer to handle, store, and transport, significantly reducing the risk of accidental ignition during ground operations and in the event of an accident. The flash point is routinely tested as a quality check; a low flash point can indicate contamination with a more volatile substance, such as Avgas.