Every crisis can also be viewed an opportunity, or so it seems. As many motorists are having trouble making ends meet with rising fuel (and food) prices, various websites are popping up (usually with affiliate schemes) that make tempting promises such as:
- “…use water as fuel and laugh at rising gas costs…”
- “double your mileage”
- “…cooler running engine…”
- “no knocking”
- “one quart of water provides over 1800 gallons of HHO gas which can literally last for months”
You will find numerous websites if you google for “water fuel car” or similar terms. Mostly the websites that make these claims sell e-books and other kits with instructions on building your own hydrogen generator from glass jars, electrodes and tubes to hook up to your existing engine.
Such kits draw power from your car’s electrical system (the battery and the generator charging it) to split water into hydrogen and oxygen gas, which is then fed into the air intake of the engine, so the hydrogen-oxygen mixture will be burnt along the air/gasoline mixture in the car’s combustion chambers. How well can such a system really work?
If a a “water-engine” as described above were to produce extra power beyond the power obtained from burning gasoline it would violate fundamental laws of physics. The First Law of Thermodynamics states that no energy is ever lost or gained, it just changes form, such as chemical energy to heat when you burn wood or heat to mechanical energy in a steam engine. An engine that uses only liquid water to produce water vapour (i.e. water plus heat) in its exhaust while providing mechanical energy violates this law of energy balance. It outputs energy with no energy going it. It would be a perpetual motion engine, which is physically impossible.
The sad fact is, people who buy these systems usually have a very rudimentary understanding of science. They take these unverified claims at face value, or are at least prepared to give them the benefit of doubt and spend money on testing unverified claims.
The “water-fuelled car” in detail
To split water (H2O) into its constituent elements hydrogen and oxygen takes electric energy. While the engine is running that energy will come from a generator driven by the engine via a belt. Just like running with your headlights on or your radio blaring will cause your engine to work a bit harder and burn more fuel, so will an electrolytic “hydrogen generator” take its toll on your gas tank.
Assuming an efficient setup, about 50-70% of the electrical energy provided will end up as chemical energy in the explosive hydrogen-oxygen mixture fed back into the engine, the rest will just warm up the water. A gasoline engine manages to convert up to 20% of the chemical energy contained in its fuel into mechanical energy, which is then available for driving the wheels or a generator. That generator converts maybe 90% of its mechanical input into electrical power. Altogether this means that burning the hydrogen returns only around 1/10 of the power originally invested into generating the hydrogen from water. It’s like you just burnt 10 litres (or gallons) of fuel in order to avoid burning one litre (or gallon).
What this of course means is that a “water-powered car” actually burns more gasoline and gets worse mileage than an unmodified car. However, the output of the “hydrogen generator” is so small and its practical negative effect on fuel mileage is so minor, you are unlikely to actually notice that, even if you accurately measure fuel economy. For example, a setup that draws 3 amperes of current from your generator (as claimed in one of the websites we’ve studied) will only use 1/20 of one horsepower (3 A x 12 V = 36 W = 0.036 kW = 0.050 hp). The difference in fuel usage is smaller than the difference between say driving with a full or a half empty fuel tank, which also changes fuel economy as a heavier car takes more power to accelerate.
The advertised fact that the “water-powered car” uses so little water (“one quart lasts for months”) is actually a give-away that the system is a hoax. If you produced hydrogen at home from tap water and a solar panel on your roof and stored it in a pressurized tank in your car to run it on only hydrogen, you would find that the amount of water used to make the hydrogen is still in the same order of magnitude as the amount of gasoline used, maybe something like a third by volume (I’d have to look up the exact numbers on relative energy content of hydrogen and hydrocarbons). In a water car that uses virtually no water (no matter where the electricty to make the hydrogen came from) the hydrogen can not be making any significant contribution to running it because there’s too little of it!
Less pinking / knocking?
I don’t know how many of the people who sell these useless plans are simply ignorant about science and how many are fully aware they’re scamming people. In any case, their other claims are equally baseless as their claims about improved fuel economy. Hydrogen has a higher energy content but also much lower octane rating than gasoline because it burns faster, more violently. This means your engine is more likely to start knocking or “pinking” than when run on gasoline (or gasoline / ethanol mixtures), not less. This is a problem that BMW had a hard time dealing with when they converted the engine of a 7-series saloon car to run on hydrogen. In practice this problem doesn’t matter in a “water car” because those “hydrogen generators” output so little hydrogen that it makes almost no difference to the engine, unlike real hydrogen cars with hydride or high pressure hydrogen tanks.
Cooler running engine?
Also, a hydrogen / oxygen mixture does not burn “cooler” than a gasoline / air mixture. Ask the space shuttle designers: The only reason the space shuttle’s hydrogen-oxygen engine doesn’t melt itself is because it’s cooled with liquid hydrogen (at -253 C / -423 F). Hydrogen / oxygen flames burn so hot they can be used for cutting steel like butter. First, hydrogen release more energy per unit of weight than does gasoline. Secondly, while the oxygen used for burning gasoline in a car engine is diluted with nitrogen (which makes up 80% of the air we breathe), the ogygen / hydrogen mix from the generator has not been diluted with anything inert, which is another reason why it burns so hot.
The vater vapour in the “water car” exhaust has no cooling effect whatsoever, because it’s not derived from liquid water, hence there’s no cooling effect from evaporation heat. Again, in the “water car” setup it makes no difference because there’s too little hydrogen involved.
In reality a “water as fuel” car is a placebo. Technically it doesn’t make any noticable difference to the amount of gasoline you use per kilometre or mile, but it may change the way you think about driving. If you do see any drop in fuel usage, it may be simply that you’re thinking more about fuel usage because of the investment you’ve just made and now drive less aggressively than before and that can indeed result in a modest reduction. Beyond that, any claimed changes are either due to wishful thinking, a vivid imagination or a cruel hoax to deceive unsuspecting customers.
The only way you’ll really see a 50% drop in your monthly fuel bill is if you basically cut your driving in half or if you change to a significantly different kind of car, such as from a bulky V6 to an economical Toyota Prius.
The number one factor that affects fuel economy around town is weight: A lighter car uses less fuel. Don’t get a more powerful engine than you really need. A more efficient setup, such as a hybrid or a new clean diesel can make a big difference too. Use public transport, ride a bicycle or walk wherever you can. It’s good for your health too 🙂
UPDATE: Here is a good page that explains in more detail why the claims for “HHO” don’t add up (use Ctrl+A to mark the text as it’s difficult to read as dark text on dark background).