How Do Hydrogen Cars Work
There is more than one way to utilize hydrogen for vehicle propulsion. When most people think of hydrogen vehicles, they are thinking of hydrogen fuel cell electric vehicles. These use a fuel cell to combine hydrogen and oxygen to get electricity.
Because hydrogen is flammable, it's possible to use it as a gas that is burnt as in most combustion engines. These engines can burn the H2 directly and operate like a standard combustion engine (such as gasoline or diesel), can burn it to generate electricity (as a diesel electric hybrid or gasoline electric hybrid might) or combine with other combustion fuels to improve efficiency (as in HHO or hydrogen-injection).
Hydrogen Fuel Cells
Many vehicles are in early production phases to test hydrogen fuel cell technology. The Honda FCX Clarity is likely the most well known, but nearly every major auto manufacturer is working on fuel cell technologies and plans to have production vehicles on the road by 2015.
Fuel cells work by combining hydrogen gas (H2) with oxygen (O) to produce water (H2O). In that process, an electron is freed and can be sent around a circuit to provide power.
Otherwise, the hydrogen fuel cell vehicle (FCHV) is like any other electric vehicle with the fuel cell providing the electricity. The efficiency of the vehicle is determined by both the amount of power the fuel cell can reliably produce for the amount of hydrogen used (i.e. it's conversion efficiency) and by the way the H2 is generated for use in the vehicle.
Most fuel cells have a loss ratio amounting to about 75%-85% efficiency - where up to a quarter of the hydrogen gas is not used. Fuel cells are becoming extremely efficient, however, with new materials replacing higher-cost precious metals in their catalysts. Pound for pound, they outperform all current battery technologies for production per kilogram and/or liter of space.
Burning hydrogen is similar to a fuel cell in that it combines hydrogen with oxygen to give off water, but produces heat in the process. This is a simpler way to utilize hydrogen (technologically), but it often involves a significantly higher usage of H2 for the same amount of power moving the vehicle. This means more hydrogen is needed to move the vehicle a given distance.
Mazda is the most notable company utilizing directly-burnt H2 in their hydrogen test vehicles. The pictured Premacy Hydrogen RE Hybrid is a plug-in hybrid which uses a Wankel Rotary Engine as its range extension engine, burning hydrogen.
Another option for burning hydrogen is to add it to another combustion fuel such as gasoline or diesel, to improve combustion efficiency. This can be accomplished by either directly injecting the hydrogen into the combustion chamber (cylinder) from stored tanks or by producing the hydrogen on-demand with electrolysis in water.
Much controversy surrounds the second method. Regardless, the addition of hydrogen gas to the combustion fuel nearly always results in higher burn efficiency and ignition, but can cause engine problems if the engine is not made for the potentially higher heat or faster burn rates associated with hydrogen.
No Matter How You Slice It..
Hydrogen is a definite FutureCar power source. Because it is so abundant, easily made, and relatively cheaper than most other sources (as well as generally more environmentally friendly), hydrogen is definitely a contender for future transportation fuels.
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