MoGas is not a recognised or approved Air BP product. It is not approved for aviation use, therefore we kindly draw your attention to the following facts relating to MoGas and its qualities in the aviation context. Please take into account the dangers of using this product before flying.
OctaneThe ‘Octane’ quality of gasoline is a measure of how well the fuel can ‘wait for the spark’ and burn smoothly when lit in the engine combustion chamber by the spark plug. Gasoline of high octane quality allows powerful, light, fuel efficient engines to be built. As these qualities are sought by aviation, AVGAS 100LL is of very high octane quality, >=99.6 Motor Octane Number. The best automotive gasoline sold to the public in Europe is typically only 88 Motor Octane Number. Therefore, if an aircraft engine requires 100LL for octane, never use automotive gasoline - the fuel will not burn smoothly in the combustion chamber, causing detonation and catastrophic failure. The Industry are very knowledgeable of octane following extensive AVGAS testing at the FAA Technical Center in the US for unleaded fuel development.
VolatilityIf the aircraft engine does not require fuel of >=99.6 Motor Octane Number, one might think all would be well with automotive gasoline. Again, this is not necessarily the case as found in aircraft Supplementary Type Certificate testing. The boiling range and vapour pressure of automotive gasoline is much broader than AVGAS. This is to allow enough fuel to be produced for the market - the UK burns about 30 million litres a day of automotive gasoline and critical the market does not run out of fuel. Such a broad volatility range is fine because the vehicles have been designed to use this fuel under the climatic conditions in the country. However, if put in an aircraft which might take-off from a hot airfield and climb to a few thousand feet, causing a drop in pressure, the gasoline can boil in the fuel lines and bubbles of vapour interrupt flow to the engine, causing erratic running/stop. AVGAS has a very tightly controlled vapour pressure/distillation to minimise such issues. This was brought into specifications in ca. 1918, one of the oldest criteria.
CompositionTo meet the huge volume demand, the refinery components which can be used in automotive fuel is very broad. Of these, the most topical at present is ethanol which is permitted at up to 5% v/v. When ethanol containing fuel comes into contact with water, e.g. as might be condensed in a wing tank overnight or while descending from altitude/cold, the ethanol can separate out into the water. This changes the properties of the remaining hydrocarbon fuel which may no longer be fit for use. Ethanol is not allowed in AVGAS/very strict limits set. Years ago, in the UK, it would be rare to see ethanol in fuel as it was too expensive. However, the European Union are keen to promote ‘renewable’ fuels and have mandated targets for the Industry and some tax incentives. So, use of ethanol in on the increase and this will continue.
Engine ValvesSome aviation engines rely on the lead additive present in AVGAS to form a cushioning layer between the engine cylinder head and valves as the valves open and close. Running on unleaded fuels, particularly during break-in, can cause excessive wear/problems. However, it should also be noted certain older engines can suffer valve problems from the lead, particularly corrosion.
Spark PlugsOne area where automotive gasoline is consistently better than AVGAS is spark-plugs. AVGAS contains the additive tetraethyl lead to enhance octane. This additive can be deposited on spark plugs which need regular cleaning/changing to prevent failure. Automotive gasoline, being unleaded, offers less deposit/better spark plug life.
AdditivesTo promote a free market/customer offers, automotive gasoline specifications permit many additive types and formulations with broad acceptance criteria. AVGAS additives are very carefully controlled to prevent untested chemicals/formulations being added which might cause in-flight issues.
Industry OversightLast, but perhaps the most important difference of all, is Industry oversight of AVGAS and automotive gasoline specifications:
- AVGAS - Aviation Industry oversight. FAA, CAA, EASA, Cessna, Piper, Diamond, Lycoming, Continental, Rotax, BP, Shell, Exxon etc. (as fuel suppliers).
- Automotive Gasoline - Car Industry oversight. Ford, GM, Renault, VW, Mercedes, CONCAWE, ACEA, BP, Shell, Exxon, etc (as fuel suppliers).
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