Autos on Monday: The Engine Looks Familiar, but It Runs on Hydrogen
November 22, 2004
By DON SHERMAN
BRIGHTLY colored signs and pennants flapping in the breeze
are all the grandness that the opening of a new filling
station usually warrants, but knots of government officials
attended elaborate ceremonies - in Los Angeles, Washington
and Berlin - at three recent ribbon cuttings.
The reason for all the attention was that the stations are
to distribute hydrogen, a substance many scientists and
policymakers consider the most promising replacement for
fossil fuels because it could eliminate pollutants from the
tailpipes of cars and trucks.
No long lines of customers were waiting at the pumps to
fill up with hydrogen, though, and there probably won't be
any for years. The likely buyers would be drivers of fuel
cell autos, but such vehicles are still research projects,
not yet for sale to the public and at least a decade away
even by optimistic estimates.
The demand for hydrogen may not have to wait for
large-scale production of fuel cells, which produce
electricity through an electrochemical reaction. A flurry
of prototypes shown recently by several automakers,
including BMW, Ford, General Motors, Mazda and
Mercedes-Benz, indicates a widespread interest in adapting
piston (and even rotary) engines to burn hydrogen directly
- just as they would use gasoline.
The longstanding hurdles to using hydrogen in vehicles,
including sparse availability and high cost, have not been
overcome. Even so, automakers say the lessons learned in
producing, storing and transporting hydrogen for today's
engines will also apply to future fuel cell cars.
In turn, creating a market for hydrogen to fuel internal
combustion engines could also break a longstanding
stalemate - the reluctance of energy companies to create a
hydrogen supply without substantial demand, and fuel cell
development stymied by the lack of a hydrogen supply
"Today, energy companies, carmakers and government agencies
realize that they have to proceed pretty much in parallel,
if not exactly in lockstep," said Peter Hoffmann, editor of
The Hydrogen & Fuel Cell Letter, a monthly publication that
covers technology developments in the field.
Hydrogen shows the greatest promise among clean fuels for a
simple reason: it contains no carbon. When gasoline - a
compound heavy in hydrogen and carbon - is burned in an
engine, most of what spews out the tailpipe contains carbon
in troublesome combinations. Carbon monoxide is poisonous;
partly burned hydrocarbons are a component of smog; and
carbon dioxide, though not regulated as a pollutant, is a
greenhouse gas linked to global warming.
Pound for pound, hydrogen packs nearly three times the
energy of gasoline. It is easy to ignite and burns faster
and hotter than gasoline. The exhaust consists mainly of
steam. The only carbon byproducts come from trace amounts
of engine oil consumed during combustion.
Relatively minor changes are needed to switch engines from
gasoline to hydrogen fuel. Some internal components, such
as the "seats" of the engine's intake and exhaust valves,
must be altered to guard against a condition called
hydrogen embrittlement, which causes metal to crack.
Because hydrogen is the lightest element - its atom has
just one proton and one electron - it is a challenge to
store enough pounds for a reasonable driving distance. BMW
is convinced that condensing it to a liquid is the best way
to go, but that requires chilling it to minus 423 degrees
Fahrenheit. Others, including G.M., prefer compressing the
gas to 5,000 pounds per square inch.
A conversion G.M. did on a Hummer H2 used three tanks
reinforced with carbon fiber to carry 12 pounds of
hydrogen, enough for a 60-mile cruise. In contrast, BMW's
design packs 24 pounds of liquid hydrogen into a
superinsulated 45-gallon tank, enough for nearly 200 miles.
The hydrogen is delivered to the engine's intake system as
a gas through electronic fuel injectors. While the ideal
ratio for maximum power is 34 parts air to 1 part hydrogen,
engineers steer clear of such rich mixtures because they
are prone to premature ignition. The ready solution is
changing the mix to at least 68 parts of air for each
increment of hydrogen, which cools combustion.
The downside is that lean mixtures reduce power. While the
Hummer's original gasoline V-8 produces 316 horsepower, the
clean, lean hydrogen-fueled version yields only 180
BMW says its technology will be fitted to a small number of
7 Series sedans that will be offered to retail customers in
three to five years. A notable difference is that these
cars will be able to run on either hydrogen and gasoline to
stretch their operating distance, which is projected to be
180 miles on hydrogen and another 375 miles on gasoline.