SAE Update - November 2021 - 13

FOCUS:POWERTRAIN
AND PROPULSION
further reduces emissions.
Stephenson emphasized the
importance of well-to-wheels
emissions analysis. " Certainly,
locally the emissions from an
electric vehicle are zero, " he said.
" One needs to factor though the
whole ecosystem; there are
emissions in manufacturing
battery systems, there are
emissions in producing energy in
many cases. Much of our energy
in North America comes from
nonrenewable sources like coal
and natural gas. "
Hydrogen is another option
gaining steam, particularly for
long-haul trucking applications.
Kenworth collaborates with
Toyota Motor North America to
develop zero-emissions
Kenworth T680 trucks powered
by Toyota hydrogen fuel-cell
electric powertrains. Burning
hydrogen in combustion engines
also is possible, but Stephenson
points out that " burning it does
create some oxides of nitrogen. "
Asked in the Q/A after his talk
why e-fuels are overlooked
despite their virtues, Stephenson
said: " What's really driving us
towards not going the e-fuel
route is that most regulatory
pressure right now is focused on
local tailpipe emissions, so zero
UPDATE
An e-fuel's climate neutrality is determined by the energy source.
local emissions. If we take a broader well-to-wheels
approach, if our regulators do that, we have some
more flexibility and transport mechanisms for energy
like liquid fuels could play a part going forward.
" When you think about the charging rate - the
fastest charger we have right now being 350 kW - the
energy going through your hand when pumping
gasoline into your car, if you take the energy content
and the flow rate, you're 'charging' your gas tank at 5
MW - 15 times the fastest electric charger. Of course, a
diesel pump at a truck stop is another order of
magnitude faster than that. So, there's a lot of
potential [for e-fuels] if the regulations allow that as
an energy transport mechanism in the future. "
[Stephenson did not discuss it, but prohibitive
pricing for at least the next decade and a dearth of
green-hydrogen production have been cited as
potential barriers to widespread e-fuel adoption.]
Another audience question for him was: " Battery
swapping could be an option to avoid long charge
times. Why not do this with medium- and heavy-duty
vehicles? "
He responded that, in his personal opinion, " there
are a couple challenges with swapping. These battery
November 2021
13
MTU
SAE Update - November 2021

Table of Contents for the Digital Edition of SAE Update - November 2021
