If you are interested in building and experimenting with fuel
reformers for much better fuel efficiency there is a group of
experimenters sharing information at:
Fuel reformers are used in the oil industry to make hydrogen. Small
units can be built for a car or genset and the refomer's hydrogen
content output burns more efficiently giving the equivalent of a big
octane boost. Also the waste heat of the engine gets utilized by the
reformer so it is no longer wasted.
This group is for experimenters only.
Fuel + steam can be cracked with engine exhaust heat plus a catalyst
or a plasma or both together.
This technology has been around a long time but car makers won't use
Here are some examples:
Here are many more patents ignored by car makers: