With the environment in trouble and fuel prices rising, most people want to do what they can do increase the efficiency of their cars. One novel solution offered by some aftermarket suppliers is a device which supposedly runs your car partially on water. This water is supposed to replace some of the gas needed to run the car, dramatically increasing fuel economy. Unfortunately, this whole concept is impossible according to the laws of physics. It is a scam designed to take advantage of consumers who don't understand the science behind car engines.
All the gizmos designed to run your car on water run in the same way. Electricity from the car's alternator is run into an installed water tank, where it splits water into hydrogen and oxygen. The hydrogen and oxygen gasses are then piped into the car's carburetor. The carburetor mixes them with more gasoline and air, and the mixture is injected into the engine's cylinders. The hydrogen burns in the cylinders along with the gasoline, producing hot gasses which power the engine. Supposedly, adding the hydrogen and oxygen mixture increases the efficiency of the engine, saving fuel.
The law of conservation of energy states that energy is neither created nor destroyed. In this system, the "fuel" starts as water. Then, energy in the form of electricity is injected into it, turning it into hydrogen and oxygen gas. Finally, the hydrogen is burned and the energy is released again in the form of heat. If the whole process were perfect, all of the energy used to produce the hydrogen gas would be recovered when the gas was burned, and the system would neither improve nor damage the engine's efficiency. Unfortunately, every time you convert energy from one form to another, some energy is lost. Powering the alternator loses energy, using electricity to create hydrogen loses energy, and burning the hydrogen loses energy. The end result is a system that will actually make your car less efficient.
Marketers of water power systems prey on the ignorance of the public in many ways. One of these is the straightforward appeal to paranoia. They say that they have a system so revolutionary that the powers that be are scared of it. The big oil companies are supposedly suppressing the system because it will stop them from making money, and environment scientists don't want something so revolutionary to put them out of a job by saving the earth from global warming. They also use scientific terminology in unscientific ways to lend their products false credibility. They will talk about their fuel cells using the "resonant frequency" of water to separate it more efficiently, or adding "electrolytes" to save energy in conversion. In reality, you simply can't get more energy out of water than you put into it, no matter what spooky techniques you supposedly use.
This system can damage your engine. Engines are carefully timed to fire at just the right moment in the stroke. When an engine misfires, it can cause knocking, decrease efficiency, and put wear on the engine. Injecting hydrogen into the engine fuel mixture makes it more readily combustible. This can cause your engine to fire prematurely. At best, it will decrease engine efficiency. At worst, it can decrease engine life.
According to The Straight Dope columnist Cecil Adams, a car runs at bout 20 to 25 percent efficiency. That means that only about 20 to 25 percent of the heat energy from the burnt fuel is actually turned into kinetic energy to move your car. The alternator is only about 60 percent efficient, and the process of converting hydrogen to water is around 70 percent efficient. Therefore, we only have 60 percent of 70 percent of 20 to 25 percent, or around 10 percent efficiency for the hydrogen once it gets burned. How much this effects the mileage of the car isn't as easy to calculate--it depends on how much water you are converting, and how much it messes with engine firing and other issues.
