Conversation so far:
why is mtbe used as a gasoline additive
Methyl tert-butyl ether (MTBE) is a blending component of gasoline, used as an oxygenate to raise the octane number and to replace tetraethyllead (TEL).
what is the benefit of raising the octane number in gasoline
In the U.S. Methyl tert-butyl ether (MTBE) has been used in gasoline at low levels since 1979 as an antiknock (octane rating) additive to prevent engine knocking.

Question: what are alternatives to prevent engine knocking
Self-contained rewrite: what are alternatives to methyl tert-butyl ether (mtbe) to prevent engine knocking