MOGAS
USE OF MOGAS AS AN AVIATION FUEL
Background
Piston powered light aircraft of modern design and capable of operating on unleaded gasoline (ULG), combined with favourable pricing of ULG over avgas, is driving the push to supply airfields with ULG to satisfy end user demand.
Gulf Aviation to providing the aviation market with quality fuels, so it is important to accurately convey the hazards associated with flying on the wrong fuel.
This information sheet explains the major differences between avgas and ULG, as well as the importance of infrastructure and Quality Assurance. It is intended to help readers make informed choices when considering aviation gasoline.
It acknowledges that segregation already exists between jet and avgas at airfields so jet fuel is not referenced here.
To the layman, it is easy to think that avgas is simply a type of ULG that has dye and lead added, and while both are made of hydrocarbons by refinery processes, that is where the similarity ends.
First; both fuels have their respective specifications to which they must comply (ULG must meet with EN228 while Avgas meets ASTM D910 and Def Stan 91-90) it is no surprise that avgas compliance is much more stringent and to meet the generally higher standards restrict refiners to only a few refinery processes.
Furthermore ULG will contain a percentage of bio-derived components (typically ethanol) which brings its own particular challenges and will be explained later.
Questions and Answers
What is the difference between avgas and MOGAS?
Avgas is the general term for aviation gasoline and the predominant fuel used to power piston powered aircraft. The bulk of this fuel in the
Avgas is made to a tightly controlled specification that reflects the application; each batch is fully traceable for consistent quality.
Even the storage and distribution of avgas is segregated from ULG and meticulously defined and monitored.
An example of the higher quality is the Octane number (the anti-knock quality of the fuel) Avgas must have an octane number of at least 100 (as implied in the 100LL name) the best ‘super unleaded’ ULG generally has no higher octane number than 89 when measured on the same method.
Mogas is unleaded fuel made for automotive use, however due to its application the QA need not be as stringent; e.g. ULG ‘turn-over’ is very high, storage stability has less impact with ULG, which will generally degrade sooner than stored avgas. Also ULG may contain additive packages (for example, detergency) which are not approved for flight, again introducing unknowns into the equation.
However, the most significant change recently has been the introduction of bio-derived content into ULG; specifically the use of ethanol.
Ethanol may be found in ULG at concentrations up to 5.75% by mass.
Ethanol content is significant as it has certain properties that affect performance as an avgas fuel in a variety of key areas and owners/operators should be aware of:-
- Ethanol is hydrophilic, which means it can absorb water, it can even draw it from atmospheric moisture
- It has less energy content than conventional hydrocarbons; affecting range
- It is corrosive to a range of materials and can affect fuel system pipes and carburettors
- Ethanol can also affect the vapour pressure of the fuel raising the risk of vapour lock in certain circumstances
Does it matter?
It can in some cases. Airfields may chose to store ULG thereby increasing the risk of miss-fuelling by introducing another grade, additionally the Quality Assurance processes which are perfectly acceptable for the production and distribution of road fuels, are lower than those employed by aviation fuels.
Consequently extra vigilance should be applied to ensure fuel quality is satisfactory when fuelling on ULG, particularly if the source of the ULG cannot be determined.
My aircraft can fly on ULG though
Many new engine/airframe combinations are approved and can safely fly on ULG.
However this information sheet is not intended to deter operators from legitimately using ULG on approved aircraft, but to reinforce the key differences between avgas and mogas; nevertheless it doesn’t remove responsibility from owners and operators to fuel aircraft in line with manufacturer recommended guidelines or as per the Pilots Operating Handbook.
Finally
To conclude; here is a list of the key operational and technical aspects of 100LL avgas again:
It is made using the highest value refinery streams to meet the high Octane number demanded.
Each batch is individually analysed to the specification and is fully traceable.
100LL is dyed blue, to aid identification and reducing the likelihood of miss-fuelling.
The distribution infrastructure is segregated and dedicated to 100LL to eliminate contamination risks.
The fuel must achieve minimum energy content and stability levels to ensure confidence in range estimation and storage respectively.
For more information
This sheet gives an overview concerning the use of mogas as an aviation fuel. If you would like to learn more or have any enquiries please click here to Contact Us.
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