Water for fuel HHO

A water-fuelled car is a automobile that is claimed to use water as its fuel or produces fuel from water onboard, with no other energy input. Water-fuelled cars have been mentioned in newspapers, popular science magazines, local news coverage, and the internet (YouTube); at least some of the claims were found to be tied to investment frauds. This article focuses on vehicles which purport to extract their energy directly from water, a process which would violate the first and/or second law of thermodynamics

In addition to claims of cars that run exclusively on water, there have also been claims that burning hydrogen or oxyhydrogen in addition to petrol or diesel fuel increases mileage. Around 1970, Yull Brown developed technology which allegedly allows cars to burn fuel more efficiently while improving emissions. In Brown's design, a hydrogen oxygen mixture (so-called "Brown's Gas") is generated by the electrolysis of water, and then fed into the engine through the air intake system. Whether the system actually improves emissions or fuel efficiency is debated. Similarly, Hydrogen Technology Applications claims to be able increase fuel efficiency by bubbling "Aquyen" into the fuel tank.
A number of websites exist promoting the use of oxyhydrogen (often called "HHO"), selling plans for do-it-yourself electrolysers or entire kits with the promise of large improvements in fuel efficiency. According to a spokesman for the American Automobile Association, "All of these devices look like they could probably work for you, but let me tell you they don't."