Twin Module: Cummins’ 2027 diesel aftertreatment system

The hardest part of emissions for a heavy-duty truck is not always the long, steady highway run. It is the cold start, the low-speed route, the stop-and-go traffic, the long idle and the changing loads. A modern diesel aftertreatment system has to treat exhaust across all of those conditions after the engine does its work.

The Twin Module Aftertreatment system is Cummins Inc.’s 2027 diesel aftertreatment architecture for X15 and X10 diesel applications. Designed for North American on-highway vehicles as emissions standards continue to advance, Twin Module is not a break from diesel. It is the next step in Cummins’ continued evolution of diesel technology.

Twin Module brings updated technology to cold starts, low-load operation, stop-and-go routes, long hauls and tough terrain while staying rooted in a familiar Cummins aftertreatment foundation.

The familiar foundation: DOC, DPF, SCR and DEF

Twin Module starts with four familiar building blocks: DOC, DPF, SCR and DEF.

First comes the diesel oxidation catalyst, or DOC. As exhaust enters the aftertreatment system, the DOC converts carbon monoxide and hydrocarbons into less harmful substances such as carbon dioxide and water vapor. It also supports regeneration of the diesel particulate filter.

Next is the diesel particulate filter, or DPF. Its job is to capture fine particles from engine combustion. Think of it as a highly engineered trap for soot also known as particulate matter, with captured material managed over time through regeneration and normal service practices.

The final major stage is selective catalytic reduction, or SCR, which focuses on nitrogen oxides, often called NOx. This is where diesel exhaust fluid, or DEF, comes in. DEF is a urea-based fluid that is introduced into the exhaust stream. When it meets hot exhaust and the SCR catalyst, it converts NOx into nitrogen and water vapor.

Together, DOC, DPF, SCR and DEF form a proven foundation for modern diesel emissions control. These are features Cummins customers have relied on for years. Twin Module builds on Cummins’ Single Module experience with this DOC-DPF-SCR approach, bringing important technology updates for 2027 without requiring customers to relearn diesel aftertreatment from scratch.

How Twin Module is configured for 2027

The Twin Module consists of two main catalyst assemblies, each with a distinct role in the aftertreatment process.

The first is the DPF assembly, which includes the DOC and DPF functions that manage carbon monoxide, hydrocarbons and particulate matter.

The second is the SCR assembly, which handles NOx reduction after DEF has been introduced and mixed into the exhaust stream.

The two-assembly layout is practical. Cummins designed the system to support a range of vehicle chassis configurations, including under-step and back of cab for on-highway commercial vehicles.

For OEMs, packaging flexibility matters. For fleets, it means the 2027 system fits into real truck applications without unnecessary complexity.

DEF dosing is another key element. Twin Module uses a single DEF doser, rather than dual dosing. DEF is injected once in the body mixer, where it mixes thoroughly before the exhaust reaches the SCR system.

Ancillary piping connects the two assemblies. Exhaust moves through the DPF assembly first, passes through the connecting section, and then enters the SCR assembly for the next stage of treatment.

Electric heating and updated catalyst technology

The biggest 2027 update is electric heating.

SCR catalysts must reach operating temperature before they can convert Nox. In steady highway operation, exhaust heat can help keep the system in its effective range. But cold starts, low-load operation and low-temperature duty cycles can make it harder for the aftertreatment system to heat up quickly and maintain operating temperature.

Twin Module addresses that challenge with two 5 kW electric heater modules powered by a 48-volt belt-driven alternator mounted on the engine. Instead of relying only on engine heat, the system can add heat when and where it is needed.

One way to think about it is a kitchen oven. A recipe does not work as intended if the oven never reaches the right temperature. Electric heating accelerates catalyst light-off, the point when the catalyst is warm enough to work effectively. That is especially important when exhaust heat alone may not be enough.

That heat supports NOx conversion during startup and low-load operation, extending effective emissions control across a broader range of real-world driving conditions.

Twin Module also uses updated catalyst technology in the SCR assembly to improve low-temperature NOx conversion across a wider range of operating conditions. Modern emissions control is not about solving one problem in one perfect operating condition. It is about helping the full system work effectively across the duty cycles trucks actually see.

Serviceability and the bottom line

None of this matters if technicians cannot service it efficiently. Cummins designed Twin Module with that in mind.

The electric heater modules use V-band clamp connections between the heater and catalyst modules, making them serviceable without replacing the whole assembly. If a heater module needs attention, the connection design keeps the job focused on the component that needs it.

Cummins has also designed the DPF assembly to meet more stringent particulate matter requirements while keeping the same catalyst volumes and the same service intervals. For fleets and maintenance teams, continuity in DPF cleaning intervals is a practical benefit.

At its core, Twin Module is a practical evolution: the same DOC-DPF-SCR foundation Cummins customers already know, now paired with electric heating and a two-assembly layout designed for 2027 X15 and X10 diesel applications.

For customers preparing for the new diesel engines, Twin Module offers a balance of familiar building blocks and new tools for 2027. It brings new technology to a familiar job: helping diesel engines meet demanding emissions requirements while continuing to support the performance, durability and uptime heavy-duty customers expect from Cummins.