Ameer Randolph
Aviation fuel, or Avgas, is a type of aviation gasoline used in aircraft with spark-ignited internal combustion engines. The most common Avgas is 100 octane, which is a measure of the fuel's ability to resist premature detonation or knock. Octane ratings are used to display the detonation resistance of the fuel, with higher octane ratings indicating greater resistance to detonation. Avgas is available in various octane ratings, such as 87 and 130, but these are less common today. The choice of Avgas depends on the specific requirements of the aircraft engine, with high-performance engines typically requiring higher octane fuels.
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What You'll Learn
Avgas 100LL: a low-lead aviation fuel
Avgas, or aviation gasoline, is used in aircraft with spark-ignited internal combustion engines. The octane rating of aviation fuel is a standard measure of its ability to withstand compression in the engine without detonating. The higher the octane rating, the more compression the fuel can withstand before detonating.
Avgas 100LL is a low-lead version of Avgas 100, widely used in general aviation. Avgas 100LL has a lot less lead than Avgas 100 while maintaining the required octane rating for most piston-engine aircraft. It is dyed blue to distinguish it from Avgas 100, which is dyed green. Avgas 100LL is safe to use in aircraft engines originally designed for lower octane grades, such as 80/87, and is approved by major aircraft engine manufacturers.
Avgas 100LL is widely available in most regions worldwide. However, there are concerns about its future availability due to its environmental impact. The aviation industry is expected to phase out leaded fuels, and in 2012, the US Federal Aviation Administration planned to replace leaded avgas with an unleaded alternative within 11 years. Unleaded avgas grades have been introduced in Europe and are being developed by companies such as Teledyne Continental Motors and Hjelmco Oil.
The high octane rating of Avgas 100LL is essential for piston-engine aircraft, which run at higher temperatures and compression ratios than car engines. The higher octane rating prevents pre-ignition and detonation, ensuring the fuel ignites only when intended. This results in better engine performance and economy.
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Jet A: a kerosene-based jet fuel
Jet A is a kerosene-based jet fuel that is the most common type of jet fuel. It is similar to diesel fuel and is used in turbine-engine aircraft. Jet A is widely used in North America and has a freezing point higher than that of the international standard, Jet A-1. The carbon number distribution of Jet A is between 8 and 16 carbon atoms per molecule.
Jet A is a performance specification rather than a chemical compound due to the wide variation in its exact composition based on the petroleum source. The requirements for jet fuel, such as freezing and smoke points, determine the range of molecular mass between hydrocarbons. Jet A is cheaper than #2 diesel and holds more energy per unit. Some jet engines can even burn diesel fuel with the right equipment.
The octane number of jet fuel is quite low, typically around 15. However, this metric is irrelevant to its use in jet engines and is more of a curiosity. Octane ratings are used to measure a fuel's ability to withstand compression in the engine without detonating, which is important for piston engines but not for jet engines.
The use of kerosene-based jet fuels like Jet A became prevalent after World War II. The British standards for jet fuel were derived from the use of kerosene in lamps, while American standards were based on aviation gasoline practices. Over time, specifications were adjusted to balance performance and fuel availability, such as by lowering the freezing point to increase fuel availability.
Synthetic jet fuels, such as Fischer-Tropsch (FT) Synthesized Paraffinic Kerosene (SPK), are also being certified for use in aviation fleets. These fuels can be blended with conventional jet fuel and offer the potential to reduce pollutants and improve air quality around airports.
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Octane rating: the standard measure of a fuel's ability to withstand compression
Octane rating is a standard measure of a fuel's ability to withstand compression in the engine without detonating. The higher the octane rating, the more compression the fuel can withstand before detonating.
The octane rating is determined by testing the fuel in a controlled environment with a variable compression ratio. The compression ratio is the amount of pressure in the engine cylinder, which is adjusted until the knocking reaches a specific intensity level. This test measures the fuel's antiknocking tendency, as increasing the compression ratio increases the chances of knocking.
In the context of aviation fuel, the octane rating is important for determining aero-engine performance. Piston airplanes, for instance, run at higher temperatures with higher compression than car engines, so they require higher octane fuel to prevent pre-ignition and detonation. The most common type of aviation gasoline (avgas) is 100 octane, which is designed to prevent premature detonation or "knock".
It is worth noting that jet fuel has a very low octane rating of around 15. However, this is irrelevant to its use in jet engines, as jet engines do not rely on the ignition of a compressed air-fuel mixture. Instead, jet engines compress only air and then inject fuel, which is why jet fuel is similar in composition to diesel fuel.
Overall, octane rating is a critical factor in the performance and versatility of gasoline engines, with higher octane ratings allowing for a wider range of operating conditions.
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Turbine engines: kerosene-based jet fuel is formulated to suit their requirements
Jet fuel, or aviation turbine fuel (ATF), is a type of aviation fuel used in aircraft powered by gas-turbine engines. Turbine engines, such as those in jet aircraft, can operate with a wide range of fuels because the fuel is injected directly into the hot combustion chamber. This means that turbine engines can use lower-cost fuels with higher flash points, which are less flammable and therefore safer to transport and handle.
The most commonly used fuels for commercial aviation are Jet A and Jet A-1, which are produced to a standardized international specification. Jet A is the most common type of jet fuel and is made from kerosene, similar to diesel fuel. Jet A is also similar to the military fuel JP-8, which is used in both turbine-powered aircraft and diesel-powered ground vehicles. Jet A-1 is an international standard with a lower freezing point, while Jet B is used for its enhanced cold-weather performance.
Kerosene-based jet fuel is formulated to suit the requirements of turbine engines. Kerosene has a higher energy density than gasoline, making it well-suited to the rigorous demands of plane turbine engines. Its combustion at elevated altitudes and efficient thrust production are critical to aviation. Kerosene-based jet fuel also has a much higher flashpoint than gasoline-based fuel, meaning it requires a significantly higher temperature to ignite. This makes it a high-quality fuel that is safe to use in air transportation.
The aviation industry's demand for jet kerosene has increased to more than 5% of all refined products derived from crude oil. This has led refiners to optimize the yield of jet kerosene by varying process techniques. Jet fuel undergoes rigorous global quality and safety standards, with international bodies providing guidelines for density, freezing point, viscosity, contamination, and more. These standards prioritize safety, efficiency, and consistency in aviation, ensuring that the aviation kerosene used in aircraft engines meets stringent quality requirements.
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Unleaded 94 Motor octane fuel: a replacement for 100LL
Avgas, or aviation gasoline, is the type of fuel used in piston aircraft engines. The most common type of avgas is 100 octane, which is a measure of the fuel's ability to resist premature detonation or "knock".
While avgas is similar to the gasoline used in cars, it is not intended for that use. One key difference is that avgas still contains tetra-ethyl lead additives to lubricate the engine, whereas lead was removed from automotive gas in 1986. Using leaded avgas in a modern car would ruin components such as the catalytic converter.
The phase-out of 100LL (low lead) avgas has been called "one of modern GA's most pressing problems". This is because 70% of 100LL aviation fuel is used by 30% of aircraft in the general aviation fleet that cannot use any of the existing alternatives.
In March 2009, Teledyne Continental Motors (TCM) announced they had tested a 94UL fuel that might be the best replacement for 100LL. This unleaded 94 motor octane fuel meets the avgas specification, including vapour pressure, but has not been fully tested for detonation qualities in all Continental engines or under all conditions.
UL94 has a minimum Motor Octane Number (MON) of 94.0, compared to 99.6 minimum for 100LL. It is important to note that UL94 is not intended to be a full replacement for 100LL. Instead, it is designed as a drop-in replacement for aircraft with lower-octane-rated engines, such as those approved for operation on Grade 80 avgas or lower.
While some have expressed opposition to 94UL, citing potential performance loss and costs to the aviation industry, it remains a viable option for aircraft with lower-octane-rated engines that cannot use existing alternatives to 100LL.
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Frequently asked questions
Avgas, or aviation gasoline, is a type of aviation fuel used in aircraft with spark-ignited internal combustion engines. It is different from the fuel used in cars, which is typically unleaded and made to run through catalytic converters for pollution reduction.
The most common type of Avgas is 100 octane, which is a measure of the fuel's ability to resist premature detonation or "knock". Other octane ratings for Avgas include 80, 87, 94, 115, and 130, but these are less common today.
Aircraft engines, particularly piston engines, run at higher temperatures and compression than car engines. Higher octane fuel prevents pre-ignition and detonation, ensuring the fuel ignites only when it is supposed to.
No, jet fuel is not suitable for use in cars with gas engines. It is, however, possible to use jet fuel in diesel-engine vehicles, although it may lack some lubricants found in regular diesel fuel.
