Truck & Off-Highway Engineering - October 2020 - 32

Q&A
Integrating ultra-low NOx technology
presents challenges

What's the biggest challenge to meeting
ultra-low NOx?
Singh: Thermal management is one of
the biggest challenges for us, specifically
when we consider NOx control in the cold
FTP [Federal Test Procedure] and lowload cycles. We looked into different avenues, how we can use electrically-heated catalysts or substrates, how we can
enhance the aftertreatment heating by
doing the exhaust bypass; we looked into
cylinder deactivation [as part of the
SuperTruck program], and we found pros
and cons of each application.
32 October 2020

Gustav
Johnson,
chief engineer
at AVL Powertrain
Engineering.

But one of the biggest challenges we're still facing is how
to control the engine-out NOx that is being produced in the
first 60 seconds - we are still working on these challenges.
We can control hot FTPs pretty well; we
are still struggling to find a reliable system that can be robust to 1.2 million miles
and can meet the low-NOx specifically in
the cold cycles and the low-load cycles
while meeting GHG standards.
What technologies make sense for lowload operation?
Johnson: When we talk about the ultralow NOx regs, there's the low-load cycle
and there's the cold FTP and the hot FTP,
and you need different approaches for all
of them. As Navtej mentioned, the hot
FTP isn't much of a challenge assuming
you have everything there for the others.
The cold FTP is all about getting hot
quickly, and the low-load cycle is about
staying hot. The technologies that allow
you to get hot quickly aren't necessarily
the same technologies that allow you to
stay hot efficiently.
Cylinder deactivation [CDA] is a good
example - it makes a lot of sense for staying warm, it's not necessarily helpful for
getting warm, as an example. There's also a
CO2 angle of it, as well. You need to get that
heat for as little extra CO2 penalty as possible, so that's going to be the key metric.
The last thing I'd add is model-based
controls - you can't wait for there to be a
problem to respond, you need to see it
coming in terms of what the catalyst is going to do 10-15 seconds into the future from
a temperature point of view. All of that will
need to be integrated to keep that temperature in that active range for the SCR
[selective catalytic reduction] catalysts.
What set of technologies are required to
meet the 2027 NOx standards?
Farrell: As we work toward 2024 and meeting 0.05, we're going to learn what it's really
going to take. The challenges are not just
FTP and RMC-SET [Ramped Mode CycleSupplemental Emissions Test], there's the
new low-load cycle and that lab test is
probably not even the greater challenge.
TRUCK & OFF-HIGHWAY ENGINEERING

FROM TOP: NAVISTAR; CUMMINS; AVL

Ultra-low NOx regulations proposed by the California Air
Resourced Board (CARB) call for 0.05 g/hp-hr tailpipe NOx in
2024, with a second stage in 2027 further reducing NOx to
0.02 g/hp-hr. A new low-load cycle will
require 0.2 g/hp-hr. Such stringent standards will lead to an increase in cost and
complexity for OEMs, explained Navtej
Singh, chief engineer for powertrain systems at Navistar, during a technical session at the SAE COMVEC Digital Summit.
"The solution we're trying to create, we
would like to see how it can live for another 5 to 10 years because the investment - we're talking hundreds of millions of dollars," he said.
Navtej Singh,
To satisfactorily meet the stricter stanchief engineer
dards, significant improvements in the
for powertrain
durability and robustness of sensors, catsystems at Navistar.
alyst and dosing technologies are still
required, Singh emphasized, and more
accurate sensing and precise actuator
systems also are needed for 2027+ emission systems. "Navistar is still looking for
more accurate solutions in NOx sensor
technology - for example, a NOx sensor
other than ±10 percent. We're expecting
to see ±3 percent," he said, adding that
relaxation in OBD (onboard diagnostics)
is also key to early adoptions.
Singh was joined on the COMVEC panLisa Farrell,
el by Lisa Farrell, director of Cummins'
director of
Accelerated Technology Center, and
Cummins'
Gustav Johnson, chief engineer at AVL
Accelerated
Powertrain Engineering. The three exTechnology Center.
perts covered a range of topics during
the virtual session.

Truck & Off-Highway Engineering - October 2020

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