Water-fuelled car
A water-fuelled car is a hypothetical motor car that uses ordinary water as its fuel.
This is not the same concept as a steam engine. A steam engine uses water to transmit energy from the fire or other heat source to the pistons or turbine that do the work of turning the engine.
This is not the same concept as a hydrogen car, though it often incorporates some of the same elements. To fuel a hydrogen car from water, energy from a power plant is used to generate hydrogen from electrolysis, which is then either burned in the car's engine or merged with oxygen to create water via a fuel cell. Both methods produce energy used to create motion. The car ultimately receives its energy from the power plant, with the hydrogen acting as an energy carrier. They should also not be mistaken for hydrogen fuel injection which introduces small quantities of hydrogen into a 'lean' fuel-air mix that would not normally burn. Hydrogen fuel injection systems are currently sold for both gasoline and diesel engines.
The water-fuelled car, on the other hand, would have to create or extract energy from the water itself with no other energy input.
Water fuelled cars have been mentioned in history books, newspaper and popular science magazines, and urban legends since the 1800s. Some accounts are of an engine that runs on water but the idea is suppressed by either Big Oil or automakers in order to safeguard their profits. "The Water Engine", a David Mamet play later made into a film, tells such a story. Claims for water fuelled power sources are often used to fraudulently extract money from gullible investors.
Chemical energy content of water
The burning of conventional fuels such as petrol (gasoline), wood and coal releases energy, which converts the fuel into substances with less energy. In the case of most fossil fuels, one of the waste products is water. This is because water is at a lower energy state than the original fuel (see enthalpy of formation).
Chemical processes do not create energy, they merely store and release it in the form of bond energy between the atoms. Water is such an abundant chemical compound in part because it is already at a very low, stable, energy level. Where water takes part in a reaction that produces energy, the material it is reacting with contains the chemical energy that is being released. For example, it is possible to make the combustible fuel Acetylene by adding Calcium carbide to water. However, the energy in this case comes from the Calcium carbide (the 'fuel'), not the water which contributes none of the chemical energy in the reaction. Carbide miner's lamps are an example of the use of this technology.
Nuclear energy content of water
It is theoretically possible to extract energy from water by nuclear fusion, and indeed, all naturally occurring water contains trace amounts of heavy water molecules in which one of the hydrogen atoms is deuterium (an isotope of hydrogen) which is useful in nuclear fusion reactions. However, this process is not claimed by water-fuelled car promoters, and there is no suggestion that any motor, small or large, has yet been proposed that can achieve this — indeed, practical nuclear fusion power plants of any kind are not yet technologically feasible. For further discussion, see Cold fusion.
Electrolytic designs
Where designs that claim to be water fuelled engines have been made public, they often involve obtaining hydrogen from water by electrolysis. The usual scheme is to use electricity (from a battery) to split water into hydrogen and oxygen — then to burn the hydrogen in a more or less conventional engine — then use some of the power of that engine to recharge the battery and thus electrolyse more water. The end result would once again be water because that is what you get when you burn hydrogen in air. In effect, you'd have a perpetual motion machine.
In practice, such a device would merely waste energy as heat. None of the processes involved are 100% efficient. This means that some electrical energy is wasted in the electrolysis stage, some heat energy is wasted in burning the hydrogen in the engine, and some of the mechanical energy of the engine is wasted in generating electricity. This means that the amount of power available for recharging the battery is considerably less than the amount of electricity needed for continued electrolysis — and the engine rapidly comes to a halt when the battery runs out of charge.
When the hydrogen is burned, the heat it creates can be converted into work by a conventional Otto cycle car engine, but the efficiency of such engines is limited by the second law of thermodynamics and is likely to be around 20%.[1][2] Because a conventional electric motor does not use heat, it can theoretically have an efficiency close to 100%. 94% efficient motors of sufficient power to drive a car are commonplace.[3]
A variation of the electrolytic design is the water fuel cell where it is claimed that hydrogen and oxygen are produced by a mysteriously efficient form of electrolysis. According to academia's conventional wisdom, this design also reduces to a perpetual motion machine and violates the first law of thermodynamics. However, it is apparent that the current popular understanding of the physics of these approaches is quite deficient, and it does not appear that a climate of zealous curiousity conducive to further investigation exists at the university level.
The gasoline pill or powder
Some sources claim that you can fill your car up with water and then add a small pill or other additive to convert the water into usable fuel, such as with the use of a carbide lamp. This has actually been done in a full-sized vehicle, as a 1980 Mother Earth News article reported. Again, the water itself cannot contribute significant energy regardless of what you do to it or what you mix it with, implying that the additive would have to contain all the energy of a full tank of fuel weighing 1,000 to 100,000 times as much (depending on how small the pill is). This would require that the additive was a safe object that contained, weight for weight, at least 1,000 times the energy density of previously known fuels and explosives. Such a concentrated form of non-nuclear energy is highly unlikely, and could easily be sold for many applications other than as a car fuel. In any event, the result would be a car fueled by the substances in the gasoline additive and not a car fuelled by water.
Specific reports
Garrett electrolytic carburettor
Henry Garrett from Dallas, Texas allegedly demonstrated a water fuelled car in 1935 which was reported on September 8, 1935 in The Dallas Morning News. The car generated hydrogen by electrolysis as can be seen by examining Garrett's patent: U.S. patent 2,006,676
US patent number 02006676 was filed on July 1st 1932 by Charles H Garrett. The patent was granted on 2nd July 1935. This patent includes drawings which show a carburettor similar to an ordinary float type carburettor but with electrolysis plates in the lower portion, and where the float is used to maintain the level of the water.
There appears to be nothing shown in the patent that could provide a new source of energy unknown to conventional science so it is likely that the energy in the electricity from the car battery would be converted to hydrogen at between 50% and 70% efficiency [1], the hydrogen would be converted to rotational kinetic energy by the motor at around 25% to 30% efficiency and that could be used to generate electricity at around 80% efficiency. Hence only between 10% to 15% of the energy taken from the battery for electrolysis would be available to recharge the battery even if the vehicle were standing still. Whilst the vehicle might run for a while, after a short time the battery would discharge to the point where electrolysis could no longer be maintained and the car would stop. Simply using the battery to drive an electric motor would have been far more efficient.