BP - British Petroleum

Aviation Gasoline

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We are committed to supplying Aviation Gasoline globally.

We supply aviation gasoline (avgas) at many of our locations.

Avgas is supplied conforming to the following specifications:

  • ASTM D910 in the US
  • DEFENCE STANDARD 91/90 in the rest of the world.
AVGAS - A Performance Fuel
Since the Wright brothers first took to the air in 1903, there have been many technical developments, one of the most significant for piston engine aircraft being the formulation of a special fuel called Aviation Gasoline (AVGAS).

Octane levels
The octane quality of a gasoline is best described as its ability to 'wait for the spark'. In the power stroke of a gasoline engine, the air and fuel mixture is compressed by the piston before being lit by the spark plug, whereupon, it must burn smoothly. Hence, the fuel must be capable of withstanding heat from the compression and radiation as the flame approaches, without spontaneously igniting. If the fuel cannot withstand these effects, it explodes and this results in a characteristic 'pinking' or 'knocking' sound from the engine.
This is very dangerous as these explosions can cause loss of power, blast metal from the piston crown, or at worst, result in total engine failure. Engine design relies heavily on fuel octane quality. High power to weight ratio, large piston diameter, high compression, and supercharging, all call for fuels of high octane quality.
AVGAS has a much higher octane quality than other aviation gasolines such as Mogas. The best quality Mogas in the world today is about 88 Motor Octane Number, MON being a measure of octane quality (0 for very poor, 100 excellent). The minimum for performance AVGAS, 100/100LL, is 99.5 MON. But this is not the end of the story because there is an even more severe test Mogas does not face: Supercharge. Supercharge is a unique test requirement for AVGAS. The test was developed to ensure AVGAS would perform under the most demanding of conditions in high performance, high power output engines. Basically, the AVGAS is run in a single cylinder, fuel injected, supercharged engine by adjusting the air fuel ratio to give maximum power. The pure chemical 'iso-octane' which gives 100 MON, can only achieve 100 performance number for Supercharge. The specification minimum for AVGAS 100/100LL is 130 performance number.
Volatility
A gasoline engine requires a fuel which is sufficiently volatile to allow easy formation of the air and fuel vapor mixture required for combustion, while not being so volatile as to cause bubbles of vapor in the fuel lines ('vapor lock') resulting in fuel starvation. Specifications are set to control these properties based on the fuel's vapor pressure and distillation characteristics. These are different for Mogas and AVGAS.
Mogas volatility is set to meet the requirements of ground based vehicle operation for particular regions and seasonal conditions. AVGAS volatility must meet far more stringent criteria for aviation use as atmospheric pressure and temperature can change dramatically during normal operations. For example, fuel warmed to 70° F on an airfield can, in a matter of minutes, experience a pressure drop of 17% as an aircraft climbs to 5,000 feet. The fuel must not cause vapor lock. Similarly, an aircraft descending from 10,000 feet to sea level can experience an almost 36° F swing in temperature. The cold fuel must still be sufficiently volatile as atmospheric pressure increases.
To meet these demanding criteria, AVGAS distillation and vapor pressure are tightly controlled. The result is a fuel which can perform in many different and severe conditions from the equator to the arctic, from sea level to many thousands feet.
Manufacture
Gasoline is manufactured from crude oil using various refinery processes to improve the quality and volume of fuel produced. Typically, a refinery will have a number of processes to make components which are then 'blended' to give a fuel of suitable quality for the market.
Mogas is manufactured using many different refinery components to meet the demands of high volume production. Components often include reformate and alkylate, high octane materials, cracked spirit - an olefinic material - possibly oxygenated materials such as ethers (e.g. methyl tertiary butyl ether), alcohols (e.g. ethanol) and a host of other possibilities. If some of these components were used for AVGAS there could be disastrous consequences as discussed below.
AVGAS can only be made from a limited set of components of the highest quality. The octane and volatility requirements generally limit the choice of alkylate, isomerate and possibly reformate. As a result, only a limited number of the world's refineries have the capability to manufacture AVGAS. No ethers or alcohols are allowed in the blend as these have a low energy content and would reduce the range of aircraft. This is also captured in a minimum energy specification for AVGAS - there is no such specification for Mogas.
Volatility A gasoline engine requires a fuel which is sufficiently volatile to allow easy formation of the air and fuel vapor mixture required for combustion, while not being so volatile as to cause bubbles of vapor in the fuel lines ('vapor lock') resulting in fuel starvation. Specifications are set to control these properties based on the fuel's vapor pressure and distillation characteristics. These are different for Mogas and AVGAS.
After manufacture, small amounts of approved ethers and alcohols may be added as fuel system anti-icing additives. However, this is strictly controlled to meet particular operational requirements. High concentration of alcohols can attack fuel system components and cause seal swelling/failure. They can entrain water into the fuel and promote phase separation into water + alcohol/fuel phases, which may cause engine failure. AVGAS specifications help protect the aviator from these hazards.
AVGAS, and other aviation fuels, are very carefully controlled at the refinery and in the distribution system to ensure no contamination by other products. Red, green and blue dye, respectively, are added to distinguish between AVGAS 80, 100 and 100LL for instance. Quality control follows every batch ensuring it is clean and on specification, ready for use. Overall, AVGAS is the highest quality gasoline a refinery can manufacture.
Specification Control
Two major specifications control AVGAS quality. The American Society for Testing and Materials through ASTM D910 and the United Kingdom Ministry of Defence through Defence Standard 91-90. These specifications are well aligned allowing any operator to confidently purchase fuel in practically any part of the world and be assured of correct performance.
All members of the industry - engine, aircraft, oil and regulatory bodies, meet regularly to ensure their customers needs are met and flight safety is maintained through the specifications. Many different specifications exist for Mogas across the globe to meet different climatic, environmental and economic requirements. Similarly to AVGAS, the specifications are agreed between the industry members. The aviation industry has no influence over these specifications, while the automotive industry has no influence over AVGAS specifications.
Lead Additives
Mogas is now mostly unleaded in many areas of the world. AVGAS 100/100LL grades both contain lead.
Mogas is of very much lower octane quality than AVGAS 100/100LL and this level of quality can be achieved without necessarily resorting to octane enhancement additives such as lead. AVGAS is of such high quality these additives must be used, but only one, 'TEL-B', is permitted.
Some engines benefit from the use of lead to help protect vulnerable engine valve seats. These could otherwise rapidly wear away, leading to loss of compression/engine failure. However, it must be said the use of lead can also give rise to problems such as spark plug fouling and attack on certain valve metallurgies.
The industry is highly aware of the environmental pressures on lead additives and is actively seeking an unleaded replacement for AVGAS. This is a challenging program and any product must meet stringent criteria to ensure flight safety and performance is maintained. BP is actively participating in this program, working with regulatory authorities, engine and aircraft manufactures. BP is seeking to ensure customers receive safe, performance products for their aircraft.
Detergent Additives and Gum
Detergent additives are now widely used in Mogas to improve engine cleanliness by reducing soot built-up on valves and injectors. These additives are not present in AVGAS because it contains additives which have been approved for aviation use and are listed in the specification.
Any new additive for AVGAS must be stringently tested to ensure a safe and satisfactory performance.
The detergent additives in Mogas have not been approved in aviation fuels/engines which operate under different conditions to ground based vehicles.
In addition, AVGAS must pass a severe storage stability test to ensure that prolonged airfield/aircraft storage does not result in excessive gum deposits which may block fuel lines and filters. High levels of gum are often linked to the detergent additives and cracked spirit used in Mogas.
The Future The Aviation Industry are currently examining options for the development of an unleaded aviation gasoline to replace the most popular Grade ‘100LL’. Air BP are undertaking a leading role in this programme and related specification development. Air BP wish to assure our customers that until a suitable alternative is developed, Avgas 100LL remains part of the BP offer for aviation fuel. We look forward to serving you now and in the future.

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