Inside the Cummins X15 and X10 Aftertreatment System for 2027

Two can be better than one. But when it comes to diesel exhaust fluid (DEF) dosing systems, Cummins is sticking with what works.

For the Cummins HELM X15 and X10 engines, that means retaining a proven single-dose DEF injector in the EPA27 Twin Module Aftertreatment system. The approach supports a critical goal: reducing complexity while maintaining familiar service intervals and fluid economy.

“There's fuel economy, like miles per gallon of diesel fuel, and then there's fluid economy, which is fuel plus diesel exhaust fluid,” said Ross Hauswald, product manager for Cummins Emissions Solutions (CES).

Using less DEF can lower fleet operating costs. With DEF priced at more than $4 a gallon, those savings can add up. High diesel prices, averaging more than $5 a gallon, can place even more pressure on total cost of operation (TCO). Managing both is key.

Hauswald said Cummins has optimized both fuel and DEF consumption for its HELM X15 and X10 engines. The X15 is expected to deliver up to a 3% improvement in fuel economy over its predecessor. It is also designed to meet EPA’s model year 2027 heavy-duty emissions standards while managing DEF consumption.

Reaching that point required extensive engineering and testing. Cummins drew on proven technology while developing new solutions to reduce emissions without compromising power or fluid economy.

Injecting DEF into the selective catalytic reduction (SCR) system of a diesel engine has long been used to reduce nitrogen oxides (NOx). To comply with stricter emissions requirements, some designs use two DEF dosers, which can add complexity and increase DEF consumption. Cummins avoided that approach with its twin module aftertreatment system.

The familiar DEF dosing system, proven over millions of miles in current Cummins diesel engines, will remain in place for the HELM X15 and X10.

“If you are dual dosing, what that truly means is you are allowing your engine to emit a relatively high amount of NOx and then planning on reducing that all in the aftertreatment space,” Hauswald said. “You need more DEF fluid than Cummins requires to do that and your fluid economy will suffer because of that.”

Hauswald said fleet customers have responded positively to learning that Cummins did not have to redesign its DEF dosing system to meet EPA emissions requirements.

“They are very excited to hear that we are not using a dual-dosing solution,” Hauswald said. “We're using the same doser, the same part number we use today. We're using it again tomorrow. There’s no change to dosing or the DEF system at all. That is a point that puts people at ease. There is some anxiety associated in the market with dual dosing from some end users.”

Twin SCR design expands capability

Meeting EPA’s model year 2027 heavy-duty emissions standards introduced engineering challenges. One of the biggest was redesigning the SCR assembly to accommodate additional catalyst and reduce NOx by more than 80%. The system needed to be larger, but extending a single canister created other concerns.

A longer canister could increase back pressure and hinder performance. It also could create fitment challenges on vehicle chassis.

Engineers ultimately selected two SCR canisters equipped with a maintenance-free heater powered by a dedicated alternator under the hood. A second heater provides quick, precise heat at the diesel particulate filter (DPF) assembly. The electric heating system does not require batteries.

The twin SCR module uses parallel exhaust flow, reducing back pressure by 44% and contributing to improved fuel economy. More efficient thermal management further supports emissions reduction during startup and low-load operation. Upstream DEF dosing helps maximize NOx reduction.

Inlet and outlet configuration options support a range of chassis installations. The aftertreatment system for the X10 is a scaled-down version of the larger X15 system.

“A big part of the elevator pitch for me would definitely be that we have to integrate everywhere, and we know what that space looks like,” Hauswald said. “We make engines for everyone. That's what we do, so we must fit everywhere.”

The DPF and diesel oxidation catalyst (DOC), housed in the DPF assembly, are designed to meet more demanding particulate matter requirements while maintaining the same catalyst volumes and service intervals. V-band clamps around the canisters provide easier access.

“Using these V-band joints, it is relatively quick and easy to disconnect them and replace a DOC or a DPF filter when that needs to happen,” Hauswald said.

That should not be often. The diesel particulate filters are engineered to last up to 800,000 miles.

Faster, more precise electric heat

Diesel aftertreatment systems use catalysts within the SCR and DPF assemblies to reduce emissions and those catalysts must reach effective operating temperatures.

Engine exhaust can be used to heat those catalysts, but it is not as quick or precise as the electric heaters Cummins uses to meet heavy-duty emissions requirements.

“We put a heater right in front of our DPF/DOC, and we have another heater in front of our SCR,” Hauswald said. “Compared to electric heat, engine exhaust is a little crude in the sense that the heat is created relatively far away and has to travel through the system and piping before arriving at the aftertreatment. With electric, we have on-demand heat when and where we need it. The heat is coming right before the catalyst and there is little delay to get that heat right where we want it.”

The heaters can be adjusted to more precisely meet customer needs across duty cycles.

The added components do not increase overall system weight. Even with the heaters and twin SCR system, engineers kept the HELM X15 and its aftertreatment system at the same weight as the previous model. The battery-free heater design also reduces maintenance and supports Cummins’ effort to limit complexity in the X15 and X10.

“One of the charter goals of the program is that we cannot impact maintenance or maintainability of the system,” Hauswald said. “We have a clear voice from the customer. We have to do the same things we do today in terms of maintenance.”

Cummins has checked several boxes in its aftertreatment for the HELM X15 and X10: maintenance-neutral, weight-conscious, power enabling and boosting fuel economy in a dependable package.