Water vapor is introduced into an inlet air stream (16) of an engine (12),
for example, by a pervaporation process through a non-porous hydrophilic
membrane (18). A water reservoir (20), which can contain contaminated
water, provides a vapor pressure gradient across the hydrophilic membrane
(18) into the inlet air stream (16), while the rate of delivery of the
water vapor to a cylinder (38-40) is self-regulated by the rate of flow
of air across the membrane. The hydrophilic membrane (18) therefore also
filters the water from the water reservoir (20) to an extent that pure
water vapor is provided to the air inlet stream (16). Delivery of water
vapor can nevertheless be controlled using a hood (26) that slides over
the hydrophilic membrane to limit its exposed surface area.
Alternatively, water vapor is introduced into one or more of the gas
streams of a fuel cell by separating the gas stream from the wet exhaust
gas stream by a hydrophilic membrane such that moisture passes across the
membrane to moisten the gas stream and thereby prevent drying out of the
proton exchange membrane.