How do antioxidants work? A friend and I are doing a project that involves the process behind manufacturing Jet A-1 and specifically the specifications highlighted in DEF 91-91. I was interested to see the information at the bottom of page 8.


Specifically:


Why are 2,6-ditertiary-butyl-phenol, 2,6 ditertiary-butyl-4-methyl-phenol and 2,4-dimethyl-6-tertiary-butyl-phenol used rather than "more common" antioxidants like ascorbic acid?
How do these antioxidants function and do they work any differently 
to biochemical antioxidants?
What factors determine the effectiveness of an antioxidant?
Why are a mixture of chemicals used at different ratio's rather than just one. Do they work more/less effectively at different temperatures for example?
1) solubility. Typical liquid fuels consist entirely of hydrocarbons and are non-polar and thus cannot dissolve polar molecules like ascorbic acid.

2) The molecules mentioned in the provided quote can form stable radicals on loss of $\ce{OH}$ group hydrogen, i.e. act as a radical trap, transforming active radicals into non-active particles. It is a typical mechanism for antioxidants to work.

3) Strongly depends on the definition of effectiveness employed. Differen applications demand different properties.

4) Because in industry people typically do not bother with isolation of individual products if a mixture can work just as well. Sure, one can isolate individual products of phenol alkylation, but it is a tiresome work, so why bother, if the mixture works just fine?