When you burn a pound of diesel or gasoline, you create approximately a pound of water vapor.

This crazy idea is to cool some or all of the exhaust of a car or truck to condense a decent fraction of the water produced.

This water would then be used for old fashioned water injection, or, more crazily, so the engine can operate with six stroke (crower) cycle.

Water injection can reduce nitrous oxide emissions, and, in diesels, reduce particulates.

A six stroke cycle alternates back and forth between a four stroke otto/diesel cycle and a two stroke steam expansion/steam exhaust cycle - water is sprayed/injected into the cylinder at the beginning of the fifth stroke, absorbs heat from the valves and cylinder walls, and becomes high pressure steam.