Truck & Off-Highway Engineering - October 2024 - 18

Detailing the
2027 CUMMINS
X15
Aftertreatment no afterthought
One of the most significant changes for Cummins' 2027
HELM X15 diesel engine compared to the current power
plant is on the aftertreatment side of the package. The
2024 X15 engines utilize a single module aftertreatment
system. The EPA 2027-compliant X15s will move to a new
twin module aftertreatment package that reportedly
achieves drastically lower emissions levels while using the
same basic technology.
Another significant update for the new X15 aftertreatment
system is the addition of an integrated heating element.
Cummins states that this approach allows for engine
efficiency and performance to be optimized without compromising
thermal management. Independent heating of
the aftertreatment system enables a reduction in NOx
without necessitating a major increase in catalyst volume
to meet the new regulations.
The electric heating system brings the catalyst to operating
temperatures more quickly at startup, which improves
low-temperature performance and minimizes nitrous
oxide (N2
Jared Holcomb, on-highway product
manager at Cummins, explains the major
design changes for the new X15 engine.
A fraction of friction
According to Marsh, the other secret to the efficiency gains of the
new X15 came from major revisions to the piston geometry. " We've
developed pistons over time through new technologies and welding
techniques, " he said. " The piston is actually a multipiece design that
is a complete welded assembly. "
Cummins engineers made the bowl smaller to improve combustion
efficiency in addition to other revisions. " The real difference is in the
height of the piston. We moved the centerline of the pin closer to the
firing deck, which reduces friction in the power cylinder, " Marsh explained.
" The closer we can get that pin towards the foreign deck the
lower the friction and side loading is going to be. That's why the piston
is so much shorter with less skirt. It's very much an evolution, but
in a much more compact design. "
The cylinder liners also underwent major changes for the EPA27
engine. " We changed and improved the flow velocity thanks to the
coolant system design changes, " said Jared Holcomb, on-highway
product manager, Cummins. " We moved to a press fit block to liner
interface which adds more support to the liner and should improve
our bore distortion, which then equates to oil consumption seal and
combustion seal improvements. "
Marsh explained the importance of reducing friction losses in an
engine of this size. " As you look at the design of the engine, what
you're trying to optimize is how much side load you've got for a given
stroke, " he said. " You're trying to reduce the friction on the walls.
We've been able to lighten the whole piston up, shorten the compression
height by moving the pin up, and that means you can get
away with a different height of the connecting rod as well. "
18 October 2024
O) emissions. N2O is more strictly regulated
by the EPA in its Phase 3 greenhouse gas regulations and is
penalized >250x more than CO2
, according to Cummins.
The heating element also enables on-demand thermal
management. Cummins states that this system is scalable
to also meet future regulation changes and is completely
maintenance-free.
Matt Wolfe
The 2027 X15 features a twin module aftertreatment package
with an integrated heating element that reportedly optimizes
engine efficiency and performance.
The harshest duty cycle that the X15 will experience is
in Australia with the road trains, which has impacted the
design of the engine for North America, Marsh said. " As
we've gone through development of the existing X15,
things like the press fit liner have been developed already.
Because we've been manufacturing that for a specific
market, we've already developed the capabilities to
integrate this technology from a manufacturing perspective, "
he explained. " There's a lot of things like that where
we've learned somewhere else and then pulled the technology
into the product for North America. "
TRUCK & OFF-HIGHWAY ENGINEERING
BOTH IMAGES: SAE/MATT WOLFE
Truck & Off-Highway Engineering - October 2024

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