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antioxidant additives are used for aviation fuel with a maximum permitted dosage is 24 mg/l. What is the reason for this maximum value ?
what would be the consequences of adding more than 24 mg/l of antioxidant to jet fuel ?
 
Answers
09/12/2008 A: keith bowers, B and B Consulting, kebowers47@gmail.com
You are referring to jet-fuel antioxidants. Aviation gasoline has a special anti-knock and other additive cocktail.
Extensive testing has shown that a dosage level of 24mg/l of the exact antioxidant specified works safely with no adverse effects. Using a higher level is illegal. If you want/need to use a higher dosage to meet the oxidation stability tests, you must prove the higher level also is not detrimental to engine performance and life.
The real question is 'why is the subject fuel oxidation stability less than usual and needs more?' Laboratory oxidation stability tests are designed to stress the fuel and provide rapid, repeatable analytic values indicative of real world performance.
Unsatisfactory lab oxidation stability may indicate the fuel would cause deposits in the fuel vaporization locations in the turbine. Adding more AOI may give a 'pass' in the lab test, but not prevent damaging deposits in the turbine fuel vaporization devices.
There are several characteristics essential to satisfactory real world performance. A fuel with excessive aromatics or olefins will have much higher radiant heat emissions from the glowing carbon during combustion. This increases the temperature of the burners and combustion chamber walls and can cause early failure. A fuel with too many olefins and diolefins, will have poor heat and oxidation stability AND generate excessive smoke in the exhaust AND overheat the burner cans. A fuel with organic acids may cause corrosion of the fuel vaporization surfaces and turbine blades and lead to very rapid blade failure. (Ironically, phenols are excellent anti-oxidant, anti corrosion compounds)
In summary, the inflexible specifications (legal requirements) for aviation turbine fuel have been developed over time to help ensure long and reliable life of the engines with minimal risk of premature failure. This is both an economic consideration and 'loss of plane and life' issue. If you ask your Company Legal Department about this, you will quickly get a 'don't you even THINK about it.'