Ask A Scientist© Engineering Archive

 > >    name
 > >    age          40s
 > >    EMAIL
 > >    Question -   Is it not possible that an engine could be produced that
 > > would use water as a fuel source and produce no pollutants.  Take water
 > > run electricity(research for the quantity that varrying
 > > voltages/amperages produced(add plenty of electrolytes, salt being an
 > > example).  Then produce an engine that has a hydrogen production section
 > > that only seperates enough hydrogen/oxygen to fuel combustion at that
 > > time.  Time it so that with the amount of electrical current applied
 > > seperates the hydrogen and oxygen at a given rate.  A High heat spark is
 > > needed to spark the flame say oh 570 degrees C.  A combustion happens the
 > > pistons move due to the expanding of the gasses.  Some of the Hydrogen
 > > and water reform to water. This can of course be reused if you
 > > want.  Naturally you want this hydrogen to be produced in the best manner
 > > say with the aid of geothermal help or solar.  The process has to be
 > > refined for efficiency but it should work am i right.

If I understand your idea, you want to separate hydrogen from oxygen, and
use the energy released when they recombine.  You realize, of course, that
the amount of energy required to separate hydrogen from oxygen is exactly
the same as the amount of energy released when they recombine, so water is
not actually being used as a fuel source in this case, but rather as an
energy-storage medium.

Tim Mooney 
===============================================

You want to use electricity to split water into hydrogen gas and oxygen
gas, and then recombine these gases in an engine to re-form the water and
generate heat.  The first problem you will run into here is conservation of
energy.  If it takes X joules of energy to split the water into H2 and O2,
then the most energy you can get back out of the H2 and O2 when you
recombine them in an engine is X Joules.  Let's say that you want to divert
Y Joules of heat energy from the engine to make the car go;  then you'll
only have X minus Y Joules left to split the exhaust water back into H2 and
O2.  You won't have enough energy to split all the water, and in the next
cycle you'll be able to split even less.  Before long, you'll have plenty
of water, but no energy left to split it with.

The second problem you'll run into is that the first scenario is overly
optimistic.  It assumes that when you change forms of energy (chemical
energy in water, electrical energy, kinetic energy of the car), you don't
lose any of it.  Strictly speaking, by the law of conservation of energy,
you don't, but it won't be in forms you can use.  Any time you convert
energy from one form to another, a lot of it just goes away as
unrecoverable heat.  This is a big effect, too.  When electricity is
generated by heat engines (such as coal-fired turbines in a power plant),
less than 30% of the energy released by the combustion actually becomes
electrical energy.  When heat engines are used to generate mechanical
energy, the best they can do is to convert about 40% of the combustion
energy into mechanical work.  Batteries are horridly inefficient.  Fuel
cells are more efficient, but there will still be substantial energy losses
in each conversion.  So, your scheme wouldn't get through many cycles even
if you didn't try to power the car with it.

Basically, you are proposing a perpetual motion machine.  You hope to
continuously extract energy from water without depleting it.  Such a
scenario sounds too good to be true, and it is, indeed, not true.  To think
through if any perpetual motion machine will work, you need to pay
attention to the energy requirements in every step of the cycle.
Inevitably, any energy you can extract in one stage of the cycle you will
have to pay back, with interest, to complete another stage of the cycle.



                Richard Barrans Jr., Ph.D.
                Chemical Separations Group
                Chemistry Division CHM/200
                Argonne National Laboratory
                9700 South Cass Avenue
                Argonne, IL 60439
                richb@anl.gov

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