Detroit Diesel’s new DD15 engine gets high marks for ease of ride and fuel efficiency

If anyone gave out awards for the most dramatic improvement to a brand image, Detroit Diesel would be a serious contender for top honors.

Not long ago, at least in geologic terms, truckers used a lot of nicknames when referring to Detroit engines, none particularly complimentary. That image, however, began to change in the late 1980s, following the ’87 launch of the four-cycle Series 60, the world’s first heavy-duty on-highway production diesel to sport integrated electronic controls. Within several years of its introduction, the Series 60 had become a best seller –– more than a million were eventually built –– and Detroit Diesel’s reputation for quality manufacturing rose steadily.

Now the engine that’s contributed mightily to DDC’s success and stature during the past 20 years is being retired, replaced by an new global platform, officially dubbed HDEP (heavy-duty engine platform), promising even greater benefits to owners and drivers –– plus, of course, compliance with current and forthcoming emissions mandates here and around the world.

The new product, the first of several that will ultimately offer a broad range of power for a variety of applications, is the DD15, a 14.8 L engine targeted at the North American on-highway market. Although a small number of its parts are borrowed from the Series 60, such as the DDEC VI electronic system, there are several new features that add to performance, economy and driver enjoyment. Among them:

• An amplified common-rail fuel system known as the ACRS. De-signed to control the entire injection sequence and improve efficiency, this component, developed with Bosch, is capable of injection pressures greater than 31,000 PSI. Much of the pressure, however, is derived hydraulically within the injectors, so the system itself is more stable and quieter than other current common-rail technologies.

• Turbo-compounding capable of generating 50 extra horsepower (and 192 lbs.-ft. of torque) from exhaust flow. At top engine speed, an axial power turbine working in tandem with the turbo spins at about 40,000 RPM. This rotational energy is transferred through a mechanism to the crankshaft, boosting power and reducing fuel consumption.

• Integrated electronically controlled hydraulic engine brake, developed with Jacobs, capable of delivering up to 570 braking horsepower.

• A more robust iron-alloy block with better coolant flow and forged-steel crankshaft and pistons designed for larger-diameter main bearings. This, too, is said to contribute to durability, longevity and lower operating noise levels.

• A lighter, stronger, one-piece cylinder head made from compacted graphite-iron, sporting two cams and four valves per cylinder.

Together, these systems offer customer value beyond the reach of even the venerable Series 60, says Mark Groeneweg, Detroit Diesel’s director of North American engine product engineering.

“We could have made the Series 60 work for the next round of EPA mandates,” he says, “but that engine was on the drawing board in the mid ’80s. We needed an entirely new platform that offered enough flexibility to carry our product line through the next decade and beyond.”

A few months ago, I tested a DD15 on a short, triangular loop in northwest Oregon, driving from Portland to Mount Hood to Hood River back to Portland. This was a largely two-lane route that offered good up- and downhill challenges.

Leaving Freightliner headquarters on Swan Island, I headed up the long, steep ramp to the southbound lanes of I-5. My ascent and gathering momentum were so effortless I began to wonder if the truck was loaded. (Company officials said the tractor-trailer weighed about 75,000 lbs.)

Traffic was light during my departure, and I soon reached the intersection of I-84, where I headed east and, attaining an appropriate velocity, set the cruise control. One of the initial characteristics first-time drivers will notice about this engine is its quiet operation. At highway speed, the two most pronounced sounds in the cab are the soft whine of tires and the muted hiss of pressurized air being squeezed through the turbocharger. I quickly discovered that this lack of audible cues made manual shifting more challenging. I normally don’t have much trouble with an Eaton straight 10, but on this voyage I was always scratching gears, much to my embarrassment.

The route toward U.S. 26, NE 181st Ave., was a tangle of stoplights, construction and heavy congestion during my pass through the area. The DD15 performed remarkably well in these conditions, allowing me to easily keep pace with my fellow motorists. Nothing seems to bother this engine on the lower side of the transmission.

Somewhere between Gresham and Sandy, the dense suburban surroundings subsided, giving way to a more rural setting. At this point I was rolling in tenth gear at the posted speed limit when I encountered the trip’s first hill (albeit a relatively small one with a grade of about five percent). As I started up the incline, the engine shed a couple hundred RPM and hovered at about 1,200. By the time I neared the crest, engine speed had dipped to 1,150. My right foot was massaging the accelerator for maximum effect. Had the pull been much longer, I probably would have grabbed a gear, but that was unnecessary at this point. Shortly, I reached the top and headed down the other side.

The knoll had been a mere dress rehearsal for the climbs ahead, which began in earnest just outside Rhododendron (elevation 2,000 ft.). On the east side of town, I drop into ninth gear and, soon thereafter, into eighth. The DD15 was puffing hard and reporting increased coolant and oil temperatures: 210 and 220 degrees, respectively. Several miles west of Government Camp, I was in full-pull mode, moving at about 35 MPH with my foot firmly planted on the accelerator. Suddenly, the engine fan leapt into action –– the first time during the trip –– and pulled the coolant temp back into the high-normal range.

Just west of the summit (elevation 4,650 ft.), the grade eased slightly and I was able to return to ninth gear and dial back the fueling just a bit. I passed the entrance for the famed Timberline Lodge and prepared to test the retarding side of the engine’s performance.

Fully deployed, the compression brake is both effective and quiet. I came off the top in ninth with very little use of the truck’s foundation brakes. Soon, I was heading north on Highway 35, which is pretty much downhill –– quite steeply at times –– all the way to Hood River, roughly 37 miles away. In that distance, I needed to apply light foot-pedal braking just three times: an impressive display of Jacobs technology, for sure.

I returned to Portland on I-84, moving at a steady 65 MPH. It was a pleasant, scenic ride, but offered little in the way of challenges to the engine. My entire trip spanned just 178 miles and lasted about five hours. Unfortunately, I’m unable to report on the fuel economy. The tanks were half full when I started the journey. Also, the in-dash driver display seemed to be stuck on 7 MPG, a number that’s probably attainable, but not on the route I’d selected –– and certainly not with my semi-professional driving techniques.

That said, though, fuel efficiency is one of the engine’s key selling points. It is reportedly more economical to operate than its predecessor, the Series 60, which was known for its miserly fuel consumption. In the coming months, the DD15 will be joined by siblings DD13 (12.8 L) and DD16 (15.6 L).

With these new advanced products, Detroit Diesel seems to have another batch of winners on its corporate hands, and that’s good news for truckers of all stripes, not to mention the company whose reputation for quality engines is now second to none.