Aviation gasoline/avgas is required
to be an all hydrocarbon product. That is, its components must
be chemicals that contain only carbon and hydrogen atoms. The
use of oxygenated, chemicals that include oxygen atoms, compounds
such as alcohols or ethers, is not permitted. Only a few select
additives are permitted and their use is strictly controlled
and limited. The primary ingredient in avgas is isooctane. This
is a special component produced in the refining process by specialized
equipment. StnaB amounts of isopentane and aromatic (ring) compounds
are also used. The isopentane allows the correct volatility
to be achieved in the final fuel blend Aromatics are used to
improve the rich mixture ratings. However, these aromatics must
be limited to achieve other specifications. Grade 80 avgas may
also contain straight-run gasoline but this component's lower
octane rating makes it unsuitable for higher octane blends.
Approved additives include alkyl-lead anti-knock additives.
Other additives are also used to then control lead deposit formation.
Color dyes are required in most grades for safety identification.
Another common, and required, additive includes oxidation inhibitors
to improve storage stability and inhibit gum formation. Theses
anti-oxidant additives also help prevent lead compound precipitation
(separation). Other additives such as corrosion inhibitors,
fuel system icing inhibitor and static dissipator additives
may also be included by agreement with the user, by the military
or by some foreign specifications. All other additives are forbidden.