Daimler Truck’s Detroit subsidiary just debuted its new range of diesel engines for 2027-2028.
Detroit Diesel has become a prominent name in heavy-duty truck engines over its nearly 90-year history, and continues to evolve and iterate upon its “clean sheet” engine platform since it first emerged back in 2007. Emissions standards on large-displacement diesel engines pressed the major players in the industry to redesign their powertrains to reduce greenhouse gas emissions (particularly nitrous oxides), and that’s been a recurring theme over the past two decades.
In that time, Detroit’s had five total generations of its on-highway and vocational diesel engines — comprising 1.2 million engines operating in fleets today — and the Gen 6 engines continue to adopt new refinements and technologies to, in the company’s own words, “navigate a rapidly changing industry landscape without compromising reliability, efficiency or power.” This new range is set to go into production as the industry has to comply with new standards on January 1, 2027.
Fundamentally, the Detroit range still comprises the DD13, DD15 and DD16 diesel engines. Depending on the unit, power and torque ranges between 425 and 605 horsepower, as well as 1,750 lb-ft to 2,050 lb-ft, respectively. The largest-capacity powertrain, the DD16, comes in with a tighter output band, totaling four available options between 560 and 605 horsepower/1,850 and 2,050 lb-ft. The DD13 has one new rating variant of 550 horsepower and 1,750 lb-ft, while the DD15 offers up two new variants of 425 hp/455 hp, with both making the same 1,900 lb-ft of torque @ 1,000 RPM.
Updates big and small define the Gen 6 Detroit lineup
While Detroit classifies this lineup as a whole new generation, refinement is a word that pops up time and again throughout its debut presentation, from several high-level changes to tweaks aimed at boosting fuel economy and cleaning up the combustion cycle to reduce emissions.
Starting with performance, Detroit fitted all Gen 6 engines an optimized asymmetric turbocharger featuring a revised compressor and turbine wheel geometry. Detroit says the new, more efficient ball bearing design introduced for Gen 5 now expands to the whole Gen 6 range, while a wastegate valve helps control airflow and improve responsiveness (particularly at high elevation) and preserves heat in the exhaust system to aid regen and NOx catalyzation. The thermal control valve introduced on the Gen 5 DD13 to increase heat output and improve aftertreatment performance is now also a feature on all Gen 6 engines, including the DD15 and DD16. By using this valve, the manufacturer promises faster regen times, more passive regens in low duty-cycle operations, no need for parked regens and (naturally) better emissions.
Detroit also overhauled the fuel system in the Gen 6 engines, simplifying the injectors inside the common rail system to improve reliability and remove potential leak points. A high-pressure, oil-lubricated pump also helps boost system fuel pressure to 2,500 bar (or ~36,250 psi), with a forged fuel rail mounted to the cam frame and stronger fuel lines incorporated to handle the that pressure. Detroit further updated the fuel filter module to include a standard heater element to reduce gelling and buildup as it enters the system, as well as handle water separation. The company claims the hand primer requires half the effort compared to its older engines.
Other enhancements in the combustion cycle include asymmetric air induction, forcing a swirl in the combustion chamber to more effectively atomize fuel, boosting efficiency and reducing emissions. A smaller piston bowl increases the overall compression ratio. the Gen 6 engines also use Miller-cycle-like camshaft timing, holding the intake valves open during the compression stroke to reduce the work of compression and reduce in-cylinder temperatures. Detroit used similar strategies in developing the Gen 5, but claims further enhancements here.
For Gen 6, the oil separator to remove oil from vapor inside the crankcase is now electronically controlled, using an electric motor instead of oil pressure to do the job. Ideally, the separator should maintain a consistent speed across the entire engine operating range, reducing sludge buildup and reducing oil consumption particularly in areas of the rev band where oil pressure wouldn’t be as high.
Speaking of oil, a new heavy-duty engine oil standard called PC-12 (Proposed Category 12) is also set to go into effect on January 1. This new set of specifications also targets emissions reductions, focusing on increased stability against oxidation, better wear protection, better sort dispersancy and prolonging the life of the Diesel Particulate Filter (DPF). Under PC-12, new limits call for a 75% reduction in NOx emissions and a 50% reduction in particulate matter versus the current generation’s engines.
So, it’s fitting that Detroit is also homing in on the oil system to also improve reliability as well as fuel efficiency and emissions. In addition to the oil separator, its Gen 6 engines also get an electronically controlled, variable displacement oil pump, with a valve to regulate the flow and reduce the work necessary to supply the oil circuit (again, aimed at improving efficiency). If the valve does fail, it reverts to full pressure all the time so the engine can still operate. In addition to the valve, Detroit revised the system so the crankshaft main bearings supply oil to two rod bearings, instead of a one-to-one design, to deliver the same level of lubrication while reducing oil pressure, and ideally reducing the engine power necessary to supply the circuit as well as oil consumption over time.
Another headline feature: Pre-Selective Catalytic Reduction (pre-SCR)
As manufacturers have to get more aggressive in reducing emissions, so too do we see more systems emerge to facilitate the process. Detroit Gen 6 engines still have their main exhaust aftertreatment system, but now there’s also a new pre-SCR system placed upstream of the main aftertreatment setup. The main ATS and DPF carry over from the previous generation, while the new pre-SCR system introduces DEF ahead of the primary aftertreatment to further reduce emissions. The hardware and functionality are identical, according to the company’s presentation, to the main SCR used since 2010.
Detroit says the pre-SCR system won’t affect the back-of-cab packaging, with the 114SD unit fitting under the cab trench and occupying the same footprint as the past generation’s aftertreatment setup.
Service intervals and production details
Even with all the updates from Gen 5 to Gen 6 powertrains, Detroit says the maintenance intervals from the old powertrain remain unchanged. The Diesel Particulate Filters will also be the same across the range, though these new engines will have new fuel filter part numbers from the old Gen 5s.
Detroit says the Gen 6 DD13 and DD15 engines will be available in January 2027. The more powerful DD16 unit, however, won’t actually enter production for another year, in January 2028. All Detroit Gen 6 engines will still be manufactured in the U.S., at its Redford, Michigan plant which also is the home for Daimler Truck North America’s engine and component research.
In the on-road application, the Detroit Gen 6 engines will be “fully compliant” with the 2027 standards, and be available for all heavy-duty Freightliner and Western Star trucks from next year forward.
