Mike Rapoport wrote:
wrote in message
oups.com...

Mike Rapoport wrote:
Water injection does not increase efficiency, it lowers it. The water
goes
in as a liquid and goes out as a gas. The energy to do that comes from
burning fuel.

Same thing is true of a steam engine. In a steam engine it is
the phase-change of the water that makes it possible to convert
the heat from burning fuel into mechanical energy.


Yes but the steam engine takes the high-energy water vapor and produces
mechanical energy while returning the water as a low energy liquid.


Actually the conversion to mechanical energy ceases before the vapor
condenses. Condensate in a turbine or even a steam piston is
undesireable.

Regarding water-injection of an internal combustion engine
I would assume the water is injected during the intake stroke,
evaporates completely or almost so near TDC and then mechanical
energy is extracted from the water vapor, along with the combustion
products, during the power stroke. One of those combustion
products was already water, so it's not like such an engine
doesn't already extract energy from expanding water vapor.

There is an increase in entropy associated with the phase change.
That energy is irretreiveably lost and probably accounts for
why the water-injected engine is less efficient than a 'dry'
engine despite the improved thermodynamic efficiency resulting
from the higher compression ratio.

But I'm not about to attempt the math. Entropy always make my
brain hurt.

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FF