Truck & Off-Highway Engineering - August 2021 - 24

Global emissions regs
demand differing
engine strategies
POWERTRAIN FEATURE
A Cummins X15
At the heart of the Jake
Brake, introduced six
decades ago, is a twoposition-variable
valve
system that has evolved
into modular technologies
for reducing emissions
and improving fuel
consumption.
Jacobs' approach uses components identical to those of its highpower
density (HPD) engine brake, meaning that their durability has
been proven over many millions of miles. When these mechanisms
are combined with disabled fuel injection in selected cylinders, the
deactivated cylinders act as a gas spring and return the compressed
energy of the air to the crank.
As many cylinders as needed can be deactivated cycle-to-cycle, improving
combustion efficiency at times of low-level torque demand. To
optimally manage cylinder shutdowns according to driving conditions,
Jacobs has collaborated with internal-combustion controls specialist Tula
Technology. By combining Jacobs' CDA with Tula's Dynamic Skip Fire
(DSF) controls technology, an advanced control strategy makes decisions
for an engine's cylinders on an individual basis to best meet torque demands
while maintaining performance yet saving fuel (www.sae.org/
news/2020/05/tula-cummins-partner-on-diesel-cylinder-deactivation).
CDA additionally improves emissions because of its heightened
exhaust temperatures. Aftertreatment temperatures are maintained
even when the engine is in low-load operation, and cooling of aftertreatment
is minimized during coasting because less air is pumped
through the engine. CDA is mostly able to improve fuel economy
through the increased load on the operating cylinders, but incremental
improvements also are gained from reducing camshaft friction,
reducing pumping losses in part-load conditions and reducing or
eliminating the use of the intake throttle.
Meeting future challenges
Independent validation tests conducted by Tula and Cummins, run on
a Cummins X15 HD Efficiency Series diesel engine and combined with
24 August 2021
HD Efficiency Series
engine equipped with
Jacobs' CDA and Tula's
diesel Dynamic Skip Fire
showed a 74% reduction in
NOx and 5% reduction in CO2
in low-load cycle performance
compared with current clean-diesel
technologies.
a well-calibrated powertrain simulation tool, revealed
impressive results. The tests followed the Federal Test
Procedure (FTP) and combined CDA with DSF software
and engine control algorithms.
CO2
emissions were reduced by 1.5% during the hot
cycle and NOx emissions by 45%. During the low load
cycle (LLC) test, CO2
was reduced by 3.7% and NOx by
66%. Moreover, at a steady engine speed of 1,000 rpm,
CDA with DSF delivered a fuel consumption improvement
of 25%. Another more-recent study on the LLC
further improved these results to a 74% reduction in
NOx, 20% savings in fuel, and 5% reduction in CO2
.
A host of new regulations is in the pipeline: CARB
HD Omnibus, EPA Phase 2 GHG standards, the EPA
Clean Trucks Initiative and the Euro 7/VII emissions
standard. Though details of these standards have yet
to emerge, it is known that by 2024 CARB is scheduled
to tighten NOx emissions regulations for low-load
drive cycles. Soon after, regulators in Europe and
China also will toughen their rules.
No longer will emissions strategies be allowed to
choose which - NOx or CO2
- is the lesser of two
evils: emissions of both will be more stringently controlled.
When this happens, there can be more focus
on what matters most: Real Driving Emissions, regardless
of if the truck spends a lot of time operating at
low loads, or any other special application drive cycle.
Either way, valvetrain technology can help the engine
meet those ultra-low limits.
Robb Janak, director of new technology at Jacobs Vehicle
Systems, wrote this article for Truck & Off-Highway Engineering.
TRUCK & OFF-HIGHWAY ENGINEERING
FROM LEFT: JACOBS VEHICLE SYSTEMS; CUMMINS
http://www.sae.org/news/2020/05/tula-cummins-partner-on-diesel-cylinder-deactivation
Truck & Off-Highway Engineering - August 2021

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