Engineering tweaks have been performed since the launch, software upgrades, changes in material, component design, etc., but all are part of the natural evolution of any complex machine. Readers may recall my initial impressions of the DD15 back in October '07 were very favorable, so what I've been waiting for is the addition of the 2010-related hardware. I can say confidently that DD15's on-road performance hasn't changed a bit, and may have improved in ways I can't quantify in a three-hour test drive. I should say, too, that I suffered no ill effects from my brief exposure to diesel exhaust fluid.
All the new stuff, of course, is downstream of the turbocharger - software, controllers, sensors, etc. notwithstanding. If there's any noticeable difference in the engine, I think it's even quieter than previous versions I've driven. At the Engineering Test Center garage in Portland, Ore., techs had a truck hooked up to some monitoring equipment. I walked within 20 feet of the truck - which was running - and all I could hear was a subtle rumble and the clicking of what I presume were the injectors, valves, and things under the rocker cover. It was amazingly quiet, I tell you, and equally so out on the road at speed.
For those who never thought an exhaust system had a place in a test drive ... welcome to 2010. The exhaust/aftertreatment system is very much a part of the engine now, and a big consideration for chassis fitters, body builders, and truckers.
There was much discussion in the early years of SCR development about where they'd hang all that new hardware. It's been resolved. Daimler Trucks North America will offer three aftertreatment configurations based on chassis requirements and the intended application.
In addition to the Blue-Tec 1-Box system, a two-box vertical system called 2V2 features separate SCR and diesel oxidation catalyst/diesel particulate filter units mounted vertically behind the cab. This configuration lends itself to applications where frame space and ground clearance are larger concerns than a clear back-of-cab area. It permits larger fuel tanks and a right-hand PTO option. It's available on day cabs in left- and right-hand mounting. The back-of-cab protrusion is said to be similar to the EPA '07 vertical DPF.
There's also the 2HV system - 2-box, horizontal DPF/vertical SCR - designed for fleets demanding large-capacity fuel tanks on shorter, 220- to 230-inch-wheelbase tractors. It'll be available on day cabs and sleeper cabs, but not on 58/60- and 70/72-inch models.
"If we hadn't chosen SCR at a very early stage, we wouldn't be ready with these various configurations now," said Randy DiBortoli, Daimler program manager for EPA 2010. "It's taken four years to get this packaging right."
Cummins will supply engines with proprietary aftertreatment systems, different from those used on Detroit Diesel engines.
Also new for 2010 is the tank for the diesel exhaust fluid. They're mounted on the left-hand side under and just behind the cab. The fill necks are fitted with a 19mm orifice so you can't get a diesel pump nozzle in there. There's also a magnetic lock ring fitted into the filler neck. DEF dispensing pumps will need to detect this ring before the fluid will flow, preventing DEF from being pumped into a diesel fuel tank.
The tanks have a temperature-controlled coolant-loop heater to keep the DEF warm in winter, and fluid lines running from the tank to the metering unit are electrically heated. A transfer pump is located on the side of the DEF tank.
The Environmental Protection Agency has granted a 70-minute grace period at startup in cold weather before DEF injection is required. On the coldest days, when the DEF might be frozen, dosing won't be required until the fluid thaws. During recent winter testing at ambient temps of minus 20 and minus 30 degrees, even with a cold-soaked, frozen-solid DEF supply, the system was dosing in just 50 minutes (tested using EPA guidelines). Real-world operating conditions will see the fluid heated faster in most cases.
In other words, you won't be sitting idle waiting for the tank to thaw. You can start up, warm up for a few minutes, and then drive away.
I split my day of driving between three trucks on two laps of the 165-mile loop Daimler uses to test trucks. It's a combination of four-lane Interstate, two-lane road with mountain grades, and stop-and-go urban traffic. It runs east out of Portland on I-84, around Mt. Hood on Highways 26 and 35, and back into the city from the south.
I got to drive three engines, actually, two DD15s and a DD13. My first drive was the red Cascadia - a customer-spec'd demo unit awaiting delivery. Its DD15 was mated to a 9-speed manual transmission, attached to a rather tall set of rear ends. It clearly wasn't set up for this terrain. It cruised 1,150 rpm at 55 mph - 150 rpm above peak torque - which is rather low for the DD15's sweet spot. It did better at 65 mph, but Oregon has a 55-mph speed limit.
On the first loop, I ran alongside a day cab equipped with a DD13 and a 10-speed, which actually out-pulled the gear-bound DD15 I was driving on the uphill side of the loop - though not through any fault of the bigger engine. I couldn't keep the engine within the proper torque range for the pull (1,100-1,200 rpm) at an appropriate road speed because the gear steps of the 9-speed were so vast. Dropping a gear put the engine speed too high, or the road speed too low. It's a flatlander, that truck.
I switched to the day cab halfway around the loop, on the downhill side, and have to say the difference in driveability was stunning. The closer steps of the 10-speed and the more reasonable 3.70 gears made all the difference.
Later in the day, I made the entire loop in a third truck, equipped with a DD15, a 10-speed Eaton UltraShift, and even taller gears than the first one. 2.64:1. A direct-drive transmission and low-pro wide-base single drive tires leveled the playing field. It worked like a charm, too.
The second DD15 and the DD13 both did a remarkable job in the hills, and pulled like champs in their peak torque ranges. Likewise on the downside, the engine brake was so strong at higher rpm that it was slowing the truck down on the grade. Switching the Jake to position 2 was the solution.
The DD13 boasts all the same features as its bigger brother (it's essentially the same engine, just a smaller package), including the broad, flat torque curve. You actually gain about 150 pounds-feet of torque as the revs fall from 1,400 to 1,100 rpm, meaning it pulls harder as the revs drop. Throttle and turbo response are like no other North American engine - in my opinion - and will please performance-demanding drivers immensely.
Driving with SCR
So, what about the SCR implications? There weren't any. The system is totally transparent to the driver. There's no need to manually intervene at any time, no switches to flip or gauges to watch -- save for the tank level for the diesel emissions fluid. So, 2010 is something of a non-event in that regard.
Another OEM has stated its engines will not need active regen events in normal service. Detroit Diesel is being a little more circumspect. DiBortoli told me that in over-the-road service, passive regeneration will continue as it always has - completely unbeknown to the driver, and driven entirely by exhaust temperature. He said active regen events will occur under conditions where