Detroit DD15 Gen 5 Showcases Durability of New Diesel Tech

The inline-six diesel has accumulated more than one billion cumulative road miles in less than a year, proving effectiveness of ThermoCoasting.

Redesigned components and new technologies resulted in a 3% improvement in fuel efficiency for the DD15 Gen 5 engine compared to the previous generation. (Detroit)

When Detroit launched the latest iteration of the DD15 inline-six diesel engine for on-highway applications, the company promised a completely updated unit that was engineered to deliver the efficiency the market expects from a heavy-duty engine platform in the Class 8 truck segment. Less than a year later, the current generation of DD15 engines have backed up the company’s claim by hitting the one-billion-mile mark of cumulative field service.

Roughly 50% of the components for the DD15 Gen 5 were new or redesigned. Improved electronic controls enabled a new feature Detroit calls ThermoCoasting. (Detroit)

“Reaching more than one billion miles in less than one year of service is not only an impressive milestone, but a true testament to the performance of the DD15 Gen 5 engine,” said Admir Kreso, chief engineer, Daimler Truck Powertrain. “Our customers have the confidence to put the DD15 Gen 5 to the test – with great success.”

The Gen 5 DD15 engine boasted several new technologies and updated features when it was launched in the first quarter of 2021. The engine was equipped with a new aftertreatment system featuring improvements such as thermo-management control. The new system also trimmed 60 lb (27 kg) off the weight from the previous iteration. It achieved this weight loss in part by deploying just one diesel particulate filter (DPF) instead of two. The filter utilizes asymmetric cell technology that traps more particulates while maintaining sufficient flow levels.

Improved electronic controls are another enhancement, which enabled a new feature Detroit calls ThermoCoasting. According to Detroit, ThermoCoasting prevents aftertreatment cool down during regen to keep the system at the optimum operating temperature. ThermoCoasting will engage engine brakes, when necessary, between 900 and 1,500 rpm while the engine mimics coasting while simultaneously maintaining zero torque at the flywheel to balance power delivery.

Powertrain noise levels during ThermoCoasting are reportedly minimal and match decibel levels observed when the engine is in the low engine brake setting. ThermoCoasting also reportedly improves aftertreatment system performance. The Gen 5 DD15 features additional thermal management upgrades such as improved cooling circuitry and greater temperature distribution across the cylinder head.

The engine was first available in January 2021 truck builds and is currently an option for Freightliner Cascadia and Western Star 49X (shown) trucks. (Western Star)

Roughly 50% of the components for the Gen 5 DD15 were new or redesigned. These include a proprietary asymmetric ball bearing turbocharger that improves performance via reduced internal friction and enables peak power and torque to be achieved at lower engine speeds. According to Detroit, peak horsepower of the Gen 5 DD15 is achieved at 1,500 rpm, compared to the prior generation’s 1,625 rpm. Peak torque is realized at 900 rpm versus a previous rating of 1,075 rpm.

A new piston bowl shape was designed to promote a swirling effect in the combustion chamber. Detroit claims this effect creates a fuel spray pattern that promotes improved fuel mixture atomization. The engine’s inlet ports were also modified. This modification combined with the new piston design and the DD15’s 21:1 compression ratio netted a three percent improvement in fuel efficiency over the previous-generation engine as well as reduced carbon dioxide emissions. These improvements for the Gen 5 DD15 also resulted in increased downspeeding.

The Gen 5 DD15 displaces 14.8 liters and the High Power engine has a peak output of 505 hp (377 kW) at 1,625 rpm and 1,850 lb-ft (2,508 Nm) torque at 975 rpm. Its GCW rating stands at 80,000 lb (36,300 kg) and it can be mated to several variations of the DT12 transmission depending on the application. The engine was first available in January 2021 truck builds and is currently an option for Freightliner Cascadia and Western Star 49X trucks.

“The award-winning DD15 Gen 5 engine is a key part of our ability to provide highly reliable service to our customers,” said Max Fuller, executive chairman and former CEO of U.S. Xpress. “The DD15 platform has been a go-to for our operations for years now and the new platform has exceeded our expectations of uptime, DPF health and overall running costs.”

Rob Reich, chief administration officer for Schneider National, echoed Fuller’s praise of the updated DD15 engine. “Our commitment to the global community to be a green transportation solution provider is closely aligned with the efficiency gains of the DD15 Gen 5 engine,” he said. “The highly efficient new engine means less hydrocarbons consumed, and an overall smaller carbon footprint for our operations.”