Mr. Green Car: Hydrogen Power
By Allen Penticoff
All motor vehicles other than pure electrics rely on hydrocarbons to provide the energy needed to power them. The fuels have hydrogen that burns with oxygen to create the power. The problem is that the carbon in hydrocarbon is useless to the combustion process, and results in air pollution and carbon build-up in the engines. If you could operate an engine on pure hydrogen, you could have the power you need without the pollution that comes from the carbon molecules. You can, and these are called “H2” cars.
There are two ways to propel a vehicle with hydrogen. One is to burn it directly in an engine; the other is to process it in a fuel cell that creates electricity. The former is very ordinary—it is indeed possible to operate a normal reciprocating engine on hydrogen with some conversion, though there are some limitations I’ll describe shortly. The latter is essentially an electric car that does not need batteries or to be plugged in, but rather filled up.
The word “hydrogen” elicits fear—visions of the Hindenburg dirigible bursting into flames and slowly collapsing in a fiery heap in 1937 at Lakehurst, N.J. While hydrogen can spontaneously combust when exposed to air at 932 degrees Fahrenheit, its flame is nearly invisible—the flames on the Hindenburg were quite visible. Most of the burning of the Hindenburg was the result of the rocket-fuel-like aluminum coatings on the fabric skin that covered it, not the bags full of hydrogen. A static spark igniting the fabric was the suspected cause of the tragedy, not a hydrogen leak. The fuel tank in your car, full of dense hydrocarbons, is arguably more dangerous than lighter-than-air hydrogen.
Hydrogen has long been obtained from water (H2O) via a process called electrolysis. Electrically-charged electrodes split the water molecules into hydrogen and oxygen. Another way to obtain hydrogen is to extract it from hydrocarbons such as natural gas, methane or ethanol.
A number of “Hydrogen Highways” exist around the U.S. and the world. Some are just outlets from commercially-piped hydrogen produced from natural gas, while others are from bio-mass and electrolysis powered by clean renewable sources. Among these are a handful of places where liquid hydrogen is available.
In Norway, they have created a 485-mile hydrogen highway from Bergen to Oslo, where the hydrogen has come from renewable resources such as landfill/bio-mass gas (methane) and hydro-electric power used in electrolysis, or from byproducts of industrial production. Solar and wind power can also be used to create hydrogen via electrolysis. Creation of hydrogen from water via renewable energy sources is very clean as compared to reformation of hydrocarbons into hydrogen. Very hopeful research indicates it may even be possible to have “home” hydrogen stations—a decentralized, on-demand system that overcomes the production and transportation problems of hydrogen. These systems may become quite common and relatively inexpensive, as we power our vehicles, homes and businesses with hydrogen.
Used in an internal combustion engine, the engine and fuel system is very similar to that of an engine operating on natural gas or propane. A different pressure tank, lines and injectors are needed. Most can operate as “dual fuel,” using either gasoline or hydrogen. However, reciprocating engines (those with pistons) have issues with the slow speed at which pure hydrogen burns, so conversions of these engines to hydrogen power have been few—among the exceptions is the liquid hydrogen burning BMW Hydrogen 7.
Automaker Mazda has discovered that their unique Wankel rotary engine does quite well burning hydrogen and is easily adapted to operate on it. (It is very difficult to describe how a “rotary” engine works—need pictures. See a diagram in motion at: http://en.wikipedia.org/wiki/Wankel_rotary. They have been around for quite a while, though—mostly made by Mazda.) The first of these was an experimental car in 1991. Now, they have a hydrogen-burning version of their RX-8 sports car, the RX-8 HRE, which is being leased to corporate customers. They also have a hybrid/hydrogen/dual-fuel version of the Mazda 5 mini-van that is in limited production. The latter makes almost too much sense—why waste ANY energy source when hybrid battery technology can reduce the consumption of fuel, hydrogen included.
When the hydrogen is burned, the only thing to come out the tailpipe is water vapor—no carbon dioxide, no nasty pollutants (except probably nitrogen oxides, but I’ve found no reference to that yet). Many critics say the fuel cell vehicle is pie-in-the-sky, that because of the inefficiency of producing, transporting and storing hydrogen, it is not worth the bother to create a whole new fuel infrastructure when one could just simply plug in an electric car and be done with it.
The problem with hydrogen-fueled vehicles is that most of the hydrogen available commercially right now is produced from natural gas. Vehicles can run just fine on natural gas, and with a higher energy density than hydrogen, you can have smaller tanks and go farther on it. So, why go through the effort to convert it to hydrogen in a vehicle, when burning natural gas in an engine is already quite clean? Despite these issues, the extra carbon-free cleanliness of hydrogen-fueled cars would seem to be worth the effort to build the needed infrastructure.
While Mazda and Honda are quite committed to a hydrogen future, most other auto manufacturers are only dabbling in fuel cell car research at present. Despite its great promise—an H2 car is not coming to your garage anytime soon. That’s sad, for it would be nice to have the sun’s fuel in our tank.
From the March 24-30, 2010 issue