Automotive Engineering - February 2023 - 27

ADVANCED PROPULSION FEATURE
BMW REAPPROACHES HYDROGEN
BMW iX5 Hydrogen during
winter testing to validate
the fuel-cell system's
performance in low
ambient temperatures.
Top engineers in Munich talk about the vital role of H2 fuel cells in the climate
crusade as iX5 pilot-fleet production begins.
by Lawrence Ulrich
A
utomakers have raised and dashed hopes for using hydrogen
to power cars and trucks, including General Motors'
notorious 2007 promise that it would sell 1 million fuel-cell
vehicles annually (actual number: zero). With EVs now seizing
the lead in showrooms and public infrastructure, hydrogen might
still seem dubious. But the complexities of global electrification have
many OEMs and policymakers willing to give our lightest atomic element
another chance.
BMW is convinced that without hydrogen supplementing the energy
mix - including for large trucks that are poor fits for battery
propulsion - the transportation sector and nations have little chance
of keeping global temperatures in check. BMW is the first German
automaker to sign onto the United Nations' " Race to Zero " pledge, as
the company aims to reach full carbon neutrality by 2050.
" Hydrogen is a versatile energy source that has a key role to play, "
said Frank Weber, member of the BMW board of management. " We
are certain that hydrogen is set to gain significantly in importance for
individual mobility. "
iX5 system details
Recently in Germany, BMW took journalists behind the scenes of the
new iX5 Hydrogen fuel-cell SUV as it kicked off pilot production, part
of a test fleet that will begin operation this spring. Based on the
South Carolina-built X5, the iX5 ditches a gasoline engine for a 125kW
(170-hp) fuel-cell stack and rear-axle electric motor. The system
is fed by an enormous pair of underfloor tanks (pressurized at an
industry-standard 700 bar/10,150 psi) that hold 6 kg (13.2 lb.) of hydrogen;
conveniently, one hydrogen kilogram holds the energy equivalent
of one gallon of gasoline. The traction motor and small 2.5-kWh
battery fill in power gaps from the fuel cell with 150 kW (200 hp),
and recapture energy via the vehicle's brakes.
The upshot is a total 275 kW (369 hp), a 500-km (311-mile) range
and 190-km/h (118-mph) top speed. Easy, EV-crushing refills take less
than five minutes. Easy, that is, if one can find an H2 oasis. Pumps for
hydrogen - currently priced around $7 to $10 per gallon in the U.S.
AUTOMOTIVE ENGINEERING
- remain scarce worldwide, with about 320 public
stations in the EU and U.S. combined. Where it's even
available, hydrogen's per-mile costs are two to three
times that of gasoline, in part because few companies
manufacture or supply the gas for retail. And that hydrogen
is almost exclusively manufactured using energy-intensive
fossil fuels, mainly natural gas.
It's the chicken-and-egg scenario from the pre-Tesla
EV era: What hydrogen passenger vehicles exist, including
a Honda CR-V-based model coming in 2024,
end up being a mirage in showrooms.
In the 2000s, BMW fiddled with burning cryogenically
stored hydrogen in the IC engines of a short run
of 7-Series sedans. Two decades later at the company's
Hydrogen Competence Center near Munich, engineers
showed their latest tech. BMW's fuel-cell system,
developed in-house, starts with wafer-thin bipolar
plates - about the size of a home A/C filter - sourced
from partner Toyota; the plates are the same as those
in the Japanese automaker's Mirai. A turbo-like electric
compressor forces hydrogen into sandwiched plate
membranes, whose catalyst separates hydrogen molecules
into protons and electrons. Those particles take
separate paths to a cathode, electrons create a flow of
electricity and water vapor is the green byproduct.
The individual cells are inspected by vision machines
to ensure no leakage of escape-prone H2. An automated
process precisely stacks and compresses hundreds
of cells. The resulting stack is sealed in a housing
and mounted in the rear carrier of the X5.
Infrastructure investments
As with previous fuel-cell bids, this might all seem quixotic.
And proponents like Thomas Hofmann, BMW hydrogen
project manager, acknowledge every hurdle. But
February 2023 27
BMW
Automotive Engineering - February 2023

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