What is Aviation Fuel? A Comprehensive Guide to Aviation Fuel

 

In the aviation transportation system, aviation fuel is the core power source ensuring the normal flight of aircraft, and its performance directly relates to flight safety, efficiency, and cost. Compared to fuels used by ground and water vehicles such as cars and ships, aviation fuel has strict requirements in terms of quality standards, composition characteristics, classification, and application, making it an indispensable key link in the aviation industry chain.

It is not ordinary fuel, but a highly refi ned, strictly regulated special petroleum product, whose quality directly impacts flight safety, operational efficiency, and even environmental sustainability.

To provide a comprehensive understanding of aviation fuel, a systematic introduction from four key dimensions is necessary: basic characteristics (what it is), quality and safety (how to ensure purity and reliability), supply chain and operations (how it reaches the aircraft), and cutting-edge trends (where it is headed in the future). This article will first introduce the basic defi nition of aviation fuel.

 

 

Aviation fuel is a type of fuel specifically designed for aircraft, needing to meet the stable operation requirements of aircraft in complex high-altitude environments (low temperature, low pressure). Therefore, its quality standards are much higher than those for fuels used in heating systems, cars, and ships. Its core characteristics are reflected in two aspects:

Safety Adaptability: By adding specific additives, the risk of fuel freezing in low- temperature high-altitude environments is reduced, while also avoiding explosion hazards caused by high temperatures and high pressures, and reducing microbial corrosion of the fuel system.

High Energy Density: Aircraft are extremely sensitive to weight, so aviation fuel needs to have a higher calorific value per unit mass ‒ approximately 18,720 BTUs per pound for aviation gasoline (1 BTU ≈ 1055.056 Joules) and approximately 18,401 BTUs for aviation kerosene, ensuring sufficient power with less fuel weight and enhancing flight endurance.

 

Based on the differences in aircraft engine types, aviation fuel is mainly divided into two major categories: aviation gasoline and aviation kerosene. The two differ significantly in composition, performance, and application scenarios.

(I) Aviation Gasoline (AVGAS): Adapted for Reciprocating Engines

Aviation gasoline is a specialized fuel for aircraft with reciprocating engines, similar in principle to civilian automotive gasoline, but with stricter requirements for anti-knock properties and composition control.

Core Characteristics: Graded by Octane Number, Anti-knock Property is Key

Octane number is a core indicator for measuring anti-knock performance: isooctane has the best anti-knock property (octane number defi ned as 100), while heptane is prone to knocking (octane number defi ned as 0). The grade of aviation gasoline represents its octane number; for example, 80-octane aviation gasoline has an anti- knock performance equivalent to a mixture of 80% isooctane and 20% heptane.

Early use of "dual-number grades": such as 100/130, where the fi rst number represents the "octane number under lean mixture conditions" (100), and the second number represents the "octane number under rich mixture conditions"

(130). High-octane models (e.g., 100/130) are suitable for high-compression engines with superchargers; currently simplified to "single-number grades," only marked by lean mixture octane number, common models being 80, 100, and 100LL.

100LL is the mainstream environmentally friendly model: Compared to 100-octane, its lead content is reduced by 50%, reducing toxicity and environmental pollution while ensuring anti-knock properties, making it the primary choice for reciprocating engine aircraft today.

Safety Differentiation: Identified by Color Dyes

To prevent mixing different grades of aviation gasoline (which could lead to engine failure or even catastrophic consequences), industry regulations require adding color dyes to the fuel, with different grades corresponding to different colors, facilitating quick identification by ground personnel.

 

(II) Aviation Kerosene (JET FUEL): Adapted for Gas Turbine Engines

Aviation kerosene, also known as "jet fuel," is the core fuel for aviation gas turbine engines (mainstream aircraft such as civil airliners and fighter jets). It features low volatility, high flash point, and good low-temperature fl uidity, and is mainly divided into two major series: civil and military.

 

Military Aviation Kerosene: Adapted for Special Needs of Military Aircraft

Military models are prefixed with "JP" (Jet Propulsion), with performance customized according to military aircraft operational scenarios (e.g., carrier-based, hypersonic flight). Common models include:

JP-4: Composition is essentially the same as JET B, focusing on low-temperature adaptability, formerly used in early military aircraft.

JP-5: Low freezing point, high flash point, specifically designed for carrier-based aircraft (to avoid safety hazards in high-temperature and high-humidity marine environments).

JP-8: Military version of JET A-1, highly versatile, currently the mainstream military aviation kerosene.

JP-6/JP-7: Customized for hypersonic engines, high flash point characteristics adapt to extreme high-temperature environments ‒ JP-6 used in the YJ93 engines of the XB-70

bomber, JP-7 used in the J58 turbojet-ramjet engines of the "Blackbird" SR-71 reconnaissance aircraft.

 

 

 

From a chemical molecular formula perspective, both aviation kerosene and ordinary kerosene are hydrocarbons (molecular formula CH3(CH2)nCH3, n=8~16), with extremely small compositional differences. It is even impossible to determine whether it is aviation kerosene by composition alone after reaching a certain purity. The core difference between the two lies in their performance specifications, which directly determine whether they can meet the requirements of aviation engines:

Calorific Value: Chinese standards require aviation kerosene to have a net calorific value ≥10,250 kcal/kg, ensuring sufficient power per unit weight of fuel; ordinary kerosene does not have such high calorific value requirements.

Density: Aviation kerosene density ≥0.775 g/cm³. Higher density means greater energy density, which can reduce the amount of fuel carried; ordinary kerosene usually has a lower density.

Low-Temperature Performance: Aviation kerosene freezing point ≤-55 ℃ ~-60 ℃ , ensuring it does not solidify at 10,000 meters altitude; ordinary kerosene has a higher freezing point (usually above 0℃) and cannot adapt to high-altitude low temperatures.

Distillation Range: The distillation range of aviation kerosene needs to be precisely controlled (usually 180~310℃, adjustable as needed), directly affecting engine starting performance and combustion completeness; ordinary kerosene has a wider distillation range and does not require strict adaptation to engine operating conditions.

Viscosity: Aviation kerosene's kinematic viscosity at 40 ℃ needs to be controlled between 1.0~2.0mm²/s ‒ too high viscosity can lead to large oil droplets and incomplete combustion, while too low viscosity can lead to short oil mist range and engine internal overheating; ordinary kerosene does not have such precise viscosity requirements.

To meet these stringent specifications, aviation kerosene uses a "single-pass partial conversion process," employing co-gel catalysts (high filling amount, low molecular sieve content) during processing to enhance aromatic saturation capacity. The final product exhibits characteristics of "high density, high smoke point, high calorific value, and low aromatics."

 

 

Aviation fuel is not an "upgraded version" of ordinary fuel, but a special fuel entirely customized around aircraft needs: in terms of c lassification, aviation gasoline is adapted for reciprocating engines, and aviation kerosene for gas turbine engines; in terms of performance, it ensures high-altitude flight safety through strict control of calorific value, density, low-temperature properties, and other indicators; in terms of production, it ensures fuel stability through specialized processes and additives. Whether for daily civil airliner commutes or special military aircraft missions, the quality and adaptability of aviation fuel are core factors determining the efficient operation of the aviation transportation system.