Daimler Truck North America customers will soon be able to order Detroit’s next-generation heavy-duty engines designed to meet EPA 2027 emissions requirements.

Starting September 1, customers can specify the Detroit Gen 6 DD13 and DD15 engines in Freightliner and Western Star trucks.

Rather than developing an entirely new engine architecture for 2027, Detroit updated its existing heavy-duty engine platform. About 75% of the Gen 6 engines’ core components carry over from the previous generation, according to Daimler Truck North America.

That approach is intended to give fleets a more familiar transition to the new emissions standards, with changes focused primarily on the fuel system, emissions controls and thermal management.

“Customers don't want to choose between proven performance and future-ready technology. With the Detroit Gen 6 engine platform, they don’t have to,” said David Carson, senior vice president of sales and marketing for DTNA.

“We’ve built on the foundation customers already know and trust while introducing targeted improvements that make the transition to EPA 2027 straightforward.”

Changing Regulations

There has been a lot of uncertainty surrounding the EPA 2027 regulations, which implement stringent new nitrogen oxide (NOx) emissions limits.

As we reported in July, the EPA proposed significant changes to its 2027 heavy-duty diesel emissions rule. The EPA proposed rule would leave in place the NOx emissions standard scheduled to take effect with 2027 model-year heavy-duty diesel engines.

However, it would delay some of the rule's costly implementation requirements, including longer useful-life requirements and expanded emissions warranties, while eliminating mandatory diesel exhaust fluid (DEF) engine derates.

The proposal also would give engine manufacturers more flexibility in how they transition to the new standards. Although comments close on that proposed rule on August 29, engine makers appear to be assuming that it is likely to become final substantially as is.

Detroit is moving ahead with its Gen 6 launch as engine makers take different approaches to EPA’s proposed flexibility for the 2027 transition. Daimler Truck North America has said it plans to move entirely to its EPA 2027-compliant Detroit lineup at the beginning of the year.

Cummins, however, announced it is changing the rollout of its EPA 2027 engines to phase in its new engines while continuing to offer current-generation models.

Paccar also has indicated it will offer pre-2027-standard engines during the transition, and International has said it's keeping its options open on the rollout of its EPA 2027 S13 engine.

What is Detroit Changing to Meet EPA 2027?

Detroit’s heavy-duty engine platform dates back to 2007, with more than 1.2 million engines sold for on-highway and vocational applications.

Rather than adding an unfamiliar emissions technology, the company emphasized that the new system builds on selective catalytic reduction technology already used in today’s trucks.

For the 2027 Gen 6 DD13 and DD15, Detroit redesigned the fuel system with a simplified architecture that provides more consistent fuel flow while maintaining fuel pressure for efficiency.

The emissions system adds a pre-SCR system along with an integrated thermal-management strategy that uses engine exhaust heat to bring the aftertreatment system up to operating temperature more quickly.

Detroit said the changes should reduce the need for parked regenerations while helping the engines meet EPA’s tougher 2027 emissions limits.

Company officials have said previously that the new EPA rule inevitably drives higher DEF consumption, but Detroit’s response is to offset that cost upstream. The Gen 6 engines will deliver approximately 3% improvement in driving fuel efficiency for a typical linehaul fleet, assuming proper thermal management and idle discipline. 

Vocational Trucks Keep Existing Packaging

For vocational fleets, one potentially important change is what isn’t changing.

Detroit said the Gen 6 aftertreatment system fits within the truck’s existing chassis space without requiring additional room behind the cab.

That means body builders and truck equipment manufacturers should be able to continue installing vocational bodies and equipment without redesigning existing upfits around a larger emissions system.

For on-highway applications, the Gen 6 engines will be available in the Freightliner Cascadia.

Three Years and 8 Million Miles of Testing

Detroit said the Gen 6 platform underwent three years of testing, including more than 8 million miles of real-world validation.

Testing included extreme temperatures, high-altitude operation, and extended idling conditions.

The Gen 6 DD13 and DD15 engines are scheduled to become available for customer orders beginning September 1 in Freightliner and Western Star trucks.