All liquid hydrocarbon-based fuels have entrained gases – air and vapour dissolved in the fuel. This has been recognised by US Research Laboratories and major engine manufacturers, though they offer no solutions as to how to mitigate this. Refined petroleum fuels can absorb up to 12% of air and diesel contains 3-10% air according to research by Cat and Cummins.

When fuel is agitated by vibration, when adding new fuel, being pumped through fuel systems, filters, fuel pumps and injectors, it absorbs air. Naturally occurring static electricity generated in the flowing fuel, increases surface tension and reduces the fuel’s ability to release the air and vapour gases in a timely manner, increasing air contamination. The longer the fuel is agitated, the more air it absorbs and entrains.

Fuel systems are often poorly designed and, failed and broken hydraulic systems make a significant contribution to fuel aeration. Air entrapment can be further exacerbated by dirty filters restricting the flow of fuel through an engine and the more it is restricted, the greater the chance of air pockets occurring.

Changing fuel temperature affects the amount of air absorbed, losing viscosity and lubricity as it heats up causing the fuel to expand and the reverse when it cools, expelling and entraining air in the process. Drivers often notice that with a full tank of new, cool fuel their engine performs better. The less fuel there is in the tank, the more air is entrained, the poorer the engine’s performance. Modern computer engine control can help eliminate the operator from ever noticing a drivability problem, whereas in carburetted equipped vehicles, drivability problems are far more noticeable.

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