THIS IS A CUT AND PASTE from another site.. The guy seems to know his stuff.
I have recently seen many people attempting to prey on unknowing consumers, who are fed up with high gas prices, by advertising a supposed system, which splits water into hydrogen and oxygen, which is injected into the engine to be used as fuel. These systems are advertised as using an electrolysis process to split water into supposed "HHO gas," using electricity from the car's battery.
Obviously this scheme was thought up by someone who had never taken so much as a high school science class. Water ( HOH, not HHO ) can be separated into hydrogen and oxygen gas, by passing an electric current through it.
H20 (liquid) ---> H2 (gas) + 1/2 O2 (gas)
As you can see, by the above balanced reaction, for each mole Water (HOH) decomposed, 1 mole H2 gas is produced, and 1/2 mole O2 gas is produced
In order to preform the above reaction (electrolysis), energy is required. this energy is produced by the car's alternator, and stored in the battery. In order to produce electricity the alternator must place a load on the car's engine.
by looking at the enthalpy of formation of the electrolysis reaction
(Δ Hf rxn = 286 kJ/mol), we see that 286 kJ of energy is required to split 1 mole (18g) of water into hydrogen and oxygen.
The electrolysis process is only 20-30% efficient, (70-80% of the energy put in is wasted as heat), however, for the simplicity of this explanations (and to satisfy sceptics and nay-sayers), we will assume 100% efficiency in the electrolysis process. The alternator which generates the electricity for the electrolysis process, again is only 50-60% efficient, but again, for the sake of simplicity we will assume 100% efficiency. Finally, the internal combustion engine of your car is only 20-30% efficient, but again, for simplicity we will assume 100% efficiency.
when the hydrogen gas produced by the electrolysis process is burned in the car's internal combustion engine, hydrogen is combined with oxygen to form water vapour (steam), in the following balanced reaction.
H2 (gas) + 1/2 O2 (gas) --> H2O (gas)
by looking at the enthalpy of formation of this reaction
(Δ Hf rxn = -241 kJ/mol), we determine that 241 kJ of energy is released by the burning of 1 mole of hydrogen.
conclusion:
we determined that to split 1 mole of water into hydrogen and oxygen gasses consumed 286 kJ of energy, assuming 100% efficiency. we also determined that burning the same amount of hydrogen that was produced released 241 kJ of energy. Even assuming 100% efficiency, we still experienced a net loss of 43 kJ (15%) of energy from this process, which supposedly lets us use water as a fuel. simple calculations show that we actually lose 15% more energy creating hydrogen than is produced by burning it. These supposed fuel saving gimmicks will actually make you burn more fuel, by forcing your alternator to work harder to generate electricity for a process which results in a net loss in energy.
by figuring in the losses in energy throughout the electrolysis process, and combustion cycle (efficiencies given earlier), we can calculate that the process is only 3-4% efficient.
at 100% efficiency, 85% of the energy used for electrolysis would be returned to the engine to preform useful work, however, in reality just 3-4% of that 85% is actually converted in to mechanical energy.
This means that for every 100 kJ of mechanical energy taken from the engine by the alternator, only 2-3 kJ of mechanical energy is produced by this so called fuel saving system.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />
