On Wed, 12 Sep 2007 23:17:40 -0700, Keith Hughes
wrote:

This, IMO, is the crux of the issue of trying to use engine heat for
evaporation (i.e. distillation), versus just preheating. For an
efficient process, the engine-to-transfer medium exchanger needs to run
with a significant delta-t, and so to does the transfer
medium-to-process exchanger. This two-step cascade would likely require
much higher engine operating temperatures than normal, with all the
attendant maintenance and longevity issues.

There is no escaping the simple fact that equipment for using the
waste heat from an engine for distillation was around for decades. Off
the shelf. It was intended for boats, of all things. RO may have
killed them off, however. Why do you insist that proven, available off
the shelf [ at one time, at least,] equipment cannot work?
Under load, the exhaust headers on my car run yellow hot, with a
ninety MPH breeze cooling them Enough temperature difference?
Something like a quarter of the fuel goes to a hot exhaust. Three
quarters of the fuel burned in a gas engine goes to waste heat.
Diesels do a bit better, and get maybe one third as shaft work.

Casady