BMW's duel Hydrogen & Gasoline Car (Internal Combustion)

From: Eunometic (eunometic_at_yahoo.com.au)
Date: 09/29/04 

Date: 28 Sep 2004 17:45:31 -0700

Will we ever see practical and affordable fuel cells cars powered by
hydrogen.

Maybe we don't need fuel cells.

BMW has produced a car, the BMW 745h (that's h for hydrogen) which
runs on both gasoline and hydrogen: this then overcomes the problem of
a limited number of hydrogen filling stations and a limited range (not
often needed) that would limit the appeal of such cars.

Although hydrogen gas has a better octane rating than petrol and is
resistent to preignition due to compression ignition that should have
rendered it an ideal internal combustion fuel it also ignites easily
due to to hot spots which are made worse due to carbon residues by
duel fuel use. The answer has usually been the Wankel Rotary or the
use of water sprays or very carefull cooling.

BMW seems to have overcome the problems on essentialy ordinary engines
by using the variable valve timing common in many cars today to phase
the valves such that they flush the combustion chamber with air and
thus cooling it more thorougly and removing carbon residues.

BMW likes using liquid hydrogen tanks and has a long and succesfull
history of doiing so but the standard 25 cubic meter 3600 psi
compressed natural gas tanks used with more than safety than standard
petrol on millions of cars and millions of forklifts world wide would
contain the equivalent of 8L (2.2 gallons US) of hydrogen. In a car
equiped with hybrid technology AND duel fuel capability that should
provide plenty of range.

Not quite the same range performance as a fuel cell car but getting
close.

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http://www.designnews.com/article/CA234389.html

H2GO: Automakers gear up for clean fuel

Hydrogen fueled cars await practical infrastructure

By Rick DeMeis, Senior Technical Editor
Design News
August 5, 2002

 
 
Montreal—The 14th World Hydrogen Energy Conference here in June
showcased hydrogen-based power technologies, especially the latest
developments in automotive applications on the verge of production.
Highlighting the latter were BMW's CleanEnergy World Tour, which
displayed the dual-fuel liquid-hydrogen/ gasoline powered 7 Series,
and Ford's Focus Fuel Cell Vehicle (FCV). Hydrogen cars produce
theoretically only water for emissions, eliminating pollution and
global warming concerns only if their fuel is produced from energy
resources, such as wind, hydro, solar, or nuclear.

BMW hopes to have its car in production in two to four years, and
certainly within the seven-year design lifetime of the current 7
Series introduced in the U.S. last year. Ford will begin low-volume
production of the gaseous hydrogen fuel-cell/battery hybrid Focus in
2004. Both will depend on a hydrogen infrastructure growing
sufficiently (and, ideally, eventually based on renewable energy) to
extend beyond limited-range and central-fueling fleet operations.

ADVERTISEMENT
   
 
Ford's gaseous-hydrogen fuel-cell/battery hybrid Focus features a 300V
Sanyo battery and a brake-by-wire electrohydraulic regenerative
braking system. The battery boosts acceleration performance but cannot
solely power the vehicle. A Ballard Power System fuel cell stack
delivers 85 kW. a 5,000-psi (345-bar) tank stores 4 kg of hydrogen and
the car has a range of 160-200 miles.

Ultimate clean machine. BMW's 745h (for hydrogen) is powered by a dual
fuel V8 internal combustion engine (ICE). Dual-fuel operation was
selected for the initial production cars because hydrogen fueling
stations will not be common at the time of the introduction, says
Christoph Huss, BMW senior VP for Science and Traffic Policy. The car
has a roughly 170-liter liquid hydrogen (LH2) tank, which holds about
9.5 kg of fuel (the energy equivalent of 50 liters of gasoline because
of LH2's 3.7 times lower energy density). Its range on hydrogen is 180
miles. Gasoline operation can run the car an additional 400 miles.

Now before you get out a calculator to see that for hydrogen this is a
gas mileage equivalent of less than 14 mpg, there are some factors to
keep in mind. With essentially two fuel supply systems, the dual-fuel
engine is optimized for gasoline operation. Huss notes hydrogen has an
equivalent octane rating of more than 110. Thus, if the engine were
designed for a higher compression ratio to better use hydrogen,
combustion efficiency would go up and the 30% loss in horsepower and
torque from being able to burn two fuels would be recovered. Once
hydrogen fueling stations become more prevalent, BMW plans to make
this design change. Then the catalytic converter could be eliminated
and reduction of nitrogen oxide emissions further optimized.

BMW chose a hydrogen ICE for propulsion, as opposed to a fuel-cell
powerplant, to optimize power, according to Franz-Josef Wetzel, head
of Future Powertrain Technology. "Each system should do what it can do
best," he emphasizes. Thus the strategy to use the ICE to deliver
power where, he says, it is most efficient at levels more than 100 kW
(134 hp), while a fuel cell is efficient in the single kW range. In
the hydrogen mode, the 4.4-liter engine produces 181 hp—a level
only possible with an ICE and offering the prospect of performance for
which BMW is noted.

In the 745h, a 5-kW UTC (United Technologies Corp.) Fuel Cells (South
Windsor, CT) unit replaces a battery. Wetzel says electricity
generation with the fuel cell is upwards of 50% efficient, more than
double that of generation by an engine driven alternator, which in
turn absorbs about 8% of ICE power. The fuel cell supplies three times
the power of an alternator for the car's 42V systems.

BMW engineers chose liquid rather than gaseous hydrogen to pack more
energy in a given volume tank. A double-walled vacuum-jacket (at 10-9
bar) tank built by Magna Steyr (Graz, Austria) holds the cryogenic
fuel at -253C. In addition, within the tank walls are 100 layers of
metallized Mylar that function similar to multiple Space Blankets,
producing an effective thickness of 100 ft of styrofoam. Pressure in
the tank is a maximum of 5-7 bar. Such low pressures offer the
prospect of non-cylindrical free-form tanks to better conform to the
volume available and maximize the quantity of fuel. Magna Steyr's
Assistant Executive VP for R&D, Jörg Buchholz, notes the European
Integrated Hydrogen Program is looking to rewrite regulations to
permit low-pressure storage in free-form tanks.

 
Carl-August Graf von Kospoth, BMW CleanEnergy project management, says
a hybrid version of the hydrogen internal combustion engine could use
an electric motor/generator to fill in the lower end of the torque
curve (green), much like current gasoline hybrids. The generator would
also regeneratively store braking energy in the car's fuel cell for
greater fuel efficiency.
For handling LH2 and filling the 745h tank, BMW and Reis Robotics
(Obernburg, Germany) engineers have developed a robotic refueling
system now in operation at a station servicing a shuttle-car test
fleet at the Munich airport. An infrared-sensing-based system locates
the filler door and fitting, then couples the refueling hose. But a
robot system isn't necessary (as evidenced at the station established
for testing in Oxnard, CA), says Huss, rather just provisions for a
driver to mate the fitting without skin being exposed to supercold
temperatures.

Design duel. Ford engineers elected to use gaseous storage for the
Focus FCV. The arguments for this are given by Kevin Casey, VP of
Stuart Energy Systems (Mississauga, Ontario, Canada), a maker of
gaseous H2 fueling stations. "Liquefying hydrogen is in-efficient and
expensive. We don't have to drill down into the arctic but into the
infrastructure to produce hydrogen on-site economically with off-peak
power," he emphasizes. But vehicle gas storage requires robust
cylindrical-shaped tanks to contain up to several-hundred-bar-pressure
hydrogen in order to provide acceptable range. BMW's Huss says
hydrogen won't be produced at each fueling site since it is more
efficient to ship LH2. On-site liquid supplies can be vaporized to
provide fuel for gaseous-based vehicles, he adds. While not agreeing
with the automaker, Casey adds, "It's good that BMW is spreading the
word on hydrogen."

In the future, to further leverage hydrogen's advantages in an ICE,
Huss sees direct injection of liquid hydrogen (rather than using the
current gaseous inlet mixture) being possible by the end of the
decade. This would boost combustion efficiency by increasing the
change in temperature (DT) in the cylinders, similar to the effect of
today's intake intercoolers. But he cautions before this can be
realized, "High pressure pumps and valves for liquid hydrogen use have
to be developed for low temperature operation." Other future
developments could see using a slurry of solid and liquid hydrogen to
increase energy density carried in the storage tank, use of more
aluminum in the engine to reduce weight, and perhaps even a
diesel-cycle engine to increase mileage.

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