FUEL CELLS—ENERGY FOR A POWER-HUNGRY WORLD - Chemistry: Notable Research and Discoveries - page 146

Fuel cells have also been used for Skylab, a space station launched
on May 14, 1973, and in orbit for more than six years, as well as in
the space shuttles. Other uses for these reliable devices include provid-
ing electricity at remote facilities that are beyond the reach of power
lines, and as back-up generators at hospitals, which cannot afford to
lose power for any length of time.
There is also the possibility of propelling vehicles. This means not
just providing electricity, as with NASA spacecraft, but also providing
the means of propulsion. Space-faring rockets require a bit too much
power for this to be practical as yet, but cars and small airplanes travel
at much more attainable speeds. Fuel cell engines are an extremely ac-
tive area of research.
Several important factors motivate this research on fuel cell en-
gines. One of these factors is the efficiency of fuel cells when compared
to engines that burn gasoline, as discussed in the following section.
EngInESAndTHErModynAMICS
The Wright brothers and Henry Ford selected a gasoline engine because
it was the best bet at the time, and it remains a popular and commonly
used engine today. But even in the early 20th century, scientists knew
that this type of engine has limits. An engine that burns gasoline or
similar fuel is a type of heat engine, which is a category of engines that
convert heat into work. The basic idea is to generate a hot, expanding
gas; in gasoline engines, this is accomplished by igniting gasoline, while
older steam engines accomplished the same goal by burning coal or
wood to boil water and make steam. Expanding gases push against a
movable rod or some other object, which in turn may rotate an axle to
power a car or drive a turbine to power a jet airplane.
Heat engines are relatively easy and inexpensive to build. Yet not
all the heat can be converted into work. Imagine lighting a fire in the
fireplace to warm a room on a cold winter day—the temperature of the
room increases, but a lot of energy is wasted because some of it heats
air that rises and escapes up the chimney. Similar losses occur in heat
engines. Engines get hot, and their temperature increases so much that
they must be cooled or they will overheat and the parts will melt. This
heat is wasted energy because it is not converted into work such as mov-
ing a car or turning a pump. Efficiency is a measure of how much of the