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All About Aviation Fuels
Flying has long captivated mankind since time immemorial.

The man’s innate dream of sailing high into the sky was after all just blueprints etched on pieces of paper. Daring enthusiasts ventured into an incipient journey, with just a rudimentary technology of the time to achieve this noble ambition of defying gravity.


The early flying machines were primitive in nature; utilizing the human-assisted power and rudimentary structures to achieve lift. Engine powered aircrafts appeared in the early 20th century. The 1903 Wright brothers’ aircraft rotary engine was gasoline powered and burned the same fuel as automobiles.


By 1940, the turbine jet engine had come of age, as it sought to alleviate the power limitations of the piston engines. Kerosene was proposed, to give life to these early turbine engines. That crucial moment in history, aviation broke the barriers to innovation, no wonder it continues to define the subtle elements of the modern society.


The aircraft stores fuel in tanks located within the wing structure. An elaborate fuel system then supplies this fuel to the engine for combustion. The fierce chemical reaction between the fuel and compressed air gives off energy that is converted to either mechanical energy or reaction propulsion.


During a clear weather, the visible white trails (contrails) left behind by Jet-powered commercial aircrafts, are clouds of condensed water vapor, released after combustion of the hydrocarbon fuel. Aviation fuels are refined from crude oil through an intricate process of fractional distillation, generating different grades of products, with varying properties.


The role of defining fuel quality and rating lies with government agencies-Ministry of defense (UK) and ASTM International (US), just to mention a few. Aviation fuels must meet certain properties before they pass the stipulated standards. Some of these are:


Energy content: This is the heat released when a particular amount of fuel combusts under controlled conditions. The energy extracted from the conversion of chemical energy into mechanical energy should be sufficient for the engine power demands.


Stability: It is the ability of the fuel to resist change to its properties.


Lubricity: It is the measure of a fuel’s competency as a lubricant. This is critical to a certain degree as fuel lubricates some moving parts in the fuel system.


Viscosity: It is the ability of a liquid to resist flow under pressure. This is particularly important as fuel introduced into the combustion chamber should be less viscous, to necessitate robust ignition.


Freezing point: It is the point at which ice crystals disappear from the fuel as the temperature increases.


Volatility: It is the ability of a fuel to change its state from a liquid to vapor. Fuel must vaporize before it combusts, however, high volatility can cause evaporative losses or vapor lock-majorly a problem with gasoline fuels.


Flashpoint: It is the lowest temperature at which vapors from a flammable fluid readily ignite at the slight introduction of an ignition source.


Fire point: The lowest temperature that fuel can maintain combustion through vaporization.


Auto-ignition temperature: Temperature at which fuel voluntarily ignites without any external input from an ignition source. 


Fuels in aviation fall into two categories; Aviation gasoline (AVGAS) and Aviation turbine (AVTUR) Aviation gasoline is well-formulated for use in aviation piston engine. The industry has settled on three grades-80UL (unleaded), 100 and 100LL (low-lead).The grade value corresponds to its octane rating.


The benchmark rating, of any gasoline fuel, is the octane rating - the measure of fuel's resistance to detonation. The high octane rating means it burns more efficiently hence enhanced engine performance. AVGAS has a higher octane rating compared to motor gasoline, the reason being that the lead additive i.e. Tetraethyllead suppresses detonation. It should be noted that the use of Tetraethyllead in automobile gasoline was abandoned in the late 20th century, due to environmental concerns.


AVGAS is denser and volatile than kerosene, furthermore, it possesses high vapor pressure. Its flash point is around -40 °, while the freezing point is approximate –58°C or lower.


During warm days, AVGAS can vaporize inside the fuel lines, and immediate components, subsequently blocking the flow of fuel in the system, this is referred to as vapor lock. For purposes of easier handling and identification, dying is necessary, to distinguish each grade of AVGAS .100LL AVGAS is dyed blue, 100 dyed green and 80UL dyed red


Additives in small quantities are added to AVGAS to improve or preserve the desired properties. These include:


Antiknock additives: The common additive is Tetraethyllead.


Icing inhibitor: These prevent ice formation in the fuel system.


Antioxidants: Inhibit or suppress oxidation reactions that lead to sedimentation and gumming.


Dyes: Color coding of distinct grades of AVGAS as a safety standard to prevent refueling with the wrong type of fuel.


Electrical conductivity additives: Prevent the event of a static electric charge to the fuel during its passage along the filters and pipes of dissimilar materials.


Corrosion inhibitor: Inhibitors approved to prevent corrosion in fuel tanks and distribution systems


Aviation turbine fuels are used in aircrafts that are powered by Gas-turbine engines. Its properties include high viscosity, lower volatility, and high boiling point compared to aviation gasoline. They may be further categorized as either kerosene type or wide-cut jet fuels. Turbine engine operates on diverse grades of AVTUR-Jet A, Jet A-1, and Jet B.


Jet B is a blend of gasoline and kerosene. It’s a wide- cut gasoline type of jet fuel, with a high volatility and low freezing point of −60 °C (−76 °F).Variants of Jet B fuels include; JP -4, JP-5 and JP-8, commonly used in military aircrafts, for their excellent cold weather performance, the drawback being a  greater fire risk during handling.


Jet A and Jet A-1 are kerosene-type of fuels with no gasoline blend. They share flashpoint and auto-ignition temperature value of 38 °C (100 °F) and 210 °C (410 °F) respectively. Jet A has a lower freezing point of −40 °, while that of Jet A-1 is −47 °C (−53 °F), making Jet A-1 suitable for high altitude flight, in addition, these excellent attributes make Jet A-1 the most preferred fuel in commercial aviation.


Aviation turbine fuels are colorless or straw-colored. Regular fuel sampling is carried out by trained personnel to detect contaminants like sediments or water. Contaminated fuel is required to be discarded. Just like in AVGAS, additives are formulated into turbine fuels to enhance performance and uphold their chemical properties. Presence of water in jet fuel creates a conductive environment for microbial growth. This can be dealt with by using biocide additives.


Synthetic and biofuels are undergoing research and could eventually replace conventional crude oil-based fuels in the near future. Refueling is carried out by ground crews, who adhere to precautionary safety measures. It is done mostly by bowsers, specially designed for such operations.


A hydrant system is an alternative way to supply jet fuel to aircrafts through an underground network of pipelines. The amount to be refueled depends on the aircraft’s maximum Takeoff weight (MTOW), which is the aircraft’s gross weight certified for a safe take off.