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The Detroit Sound

Posted: August 1, 2014 by Jim Park

We’re witnessing a huge change in the way trucks and engines come together. We saw it first with Volvo’s D-platform engines (shared with Mack and Renault). International is sharing an engine platform with European truck maker MAN (the MaxxForce Big Bore engines). And PACCAR is moving forward with the North Americanization of the European 12.9-liter Paccar MX engine that powers DAF trucks overseas.

Late last year, following an investment of $1.5 billion, Daimler Trucks AG unveiled the DD15 engine at Detroit Diesel’s Redford, Mich., assembly plant. It will be the first in a three-displacement family that will eventually power all Daimler Group trucks worldwide.

Developed from the get-go as a global engine platform, the DD15 will replace the four distinct engine series used today by Daimler Trucks brands around the world. Fully 90 percent of the componentry will be common, and as the engine rolls out in different markets over the next three years, they’ll be tailored to local demands and local emissions requirements.

The first model we’ll see in Canada, with full production set for this upcoming April, is the 14.8-liter version of the DD15. In 2010, we’ll see a larger 15.6-liter version, which will be essentially the same engine save for a longer stroke — giving it the larger displacement. Detroit Diesel says we’ll see 630 hp and 2,050 lb ft of torque out of that one. The 12.8-liter DD13 will launch in 2009, as the MBE 4000 heads for retirement in 2010.

Everything’s New:

This engine isn’t a repurposed and repackaged Series 60. It’s a brand new clean-slate design, born EPA-’07-compliant. It’ll meet the next round of EPA regs by way of cooled EGR and a particulate filter, and it’s ready to meet EPA ’10 with the addition of just a downstream selective catalytic reduction (SCR) exhaust aftertreatment system to meet the lower NOx standards. It’ll go out way beyond 2010, too, because engineers went with a long-term emissions-reduction strategy.

The DD15 is a 14.8-liter, in-line-six with four valves per cylinder and two overhead camshafts. Detroit Diesel says the hollow camshafts lowers the weight and inertia of the camshaft, improving throttle response. The camshafts play no role in building pressure at the fuel injector so the cams can be tubular and still have more than adequate strength. A gear-driven high-pressure pump maintains pressure in the common rail, with the pressure amplification accomplished inside the injector within the cylinder head.

The DD15 has a stiffer, stronger cast-iron alloy block that dramatically reduces noise and vibration. It’s got a rear gear train, and a forged-steel, counter-weighted crankshaft with huge main- and rod-bearing journals for long life and high load-bearing capacity.

The cylinder liners feature a unique bottom stop that allows the bottom of the liner to rest in the block. This mounting method also allows for improved coolant flow around the liner. The liners are thick too, which, Daimler says, leads to longer life and minimizes vibration.

The primary turbocharger is visible here, behind
the air intake. The turbo-compound is beneath the sheet-steel
heat shield, just below the EGR mixer valve.

Liner cavitation shouldn’t be an issue at all with the DD15. This engine was designed with higher coolant flow and optimized coolant galleries to avoid hotspots, which could lead to cavitation, and the rad header features a very efficient surge tank to maintain cooling system pressure while de-aerating the coolant.

Fuel and Air Management:

There’s a lot of new stuff going on inside the DD15, but two particular features give the DD15 its personality and performance characteristics: the Amplified Common Rail System (ACRS) fuel injection system, and turbo-compounding.

ACRS develops injection pressures up to 32,000 psi in a two-stage process. A gear-driven high-pressure fuel pump produces pressures in the common rail of 12,000 psi, while the final pressure boost is achieved hydraulically within the injector itself. The system is capable of up to five injection events per cycle, optimizing combustion efficiency while reducing noise dramatically.

And last but certainly not least are the turbochargers. There are indeed two of them, but they’re not series turbos as we see on Caterpillar engines. The DD15 uses a simple pre-1999 design — without complex waste-gating or variable-geometry vanes — primary turbo to boost manifold pressure for intake air management.

The second turbocharger creates the manifold pressure differential required for exhaust gas recirculation, and it pumps an extra 50 hp or so back into the drivetrain.

The combination of ACRS, turbo-compounding, and the rapid response of the primary turbocharger means that the DD15 exhibits up to 75-percent better torque response than the current Series 60 engine — meaning it spools up to peak torque very quickly, in 1.5 seconds as opposed to more than four seconds as is the case on many other engines.

The Sum of DD15’s parts:

Journalists who attended the launch got about 10 minutes of wheel time with the DD15 on the test track at the Chrysler Proving Grounds in Chelsea, Mich. That just piqued my curiosity, so, I cashed in nearly all of my chips with my friends at Freightliner and Detroit Diesel and got permission to take the truck out on my own for six hours the following day.

Equipped with the DD15, Freightliner’s Cascadia should
be one of the quietest, fuel-efficient trucks on the road.

I think drivers are going to be really, really, happy with the DD15 — once they get used to the fact that it has quite a different personality than anything they have driven before. They might mistake it for flat and unresponsive. I can promise you, the DD15 is anything but flat and unresponsive.

What’s missing is the turbo lag present on virtually every North American engine currently in service. On other engines, it takes a moment for the turbo to spool up and build boost pressure after an upshift. When the turbo is up to speed and the manifold pressure reaches 20 to 30 psi, the driver hears the whine and feels a surge of power. Turbo lag is virtually non-existent on the DD15. It spools up to full boost in about 1.5 seconds, compared to three or four seconds on other engines. Drivers will barely hear the turbo whine, and they won’t feel the post-lag surge they’re used to because the turbo comes up to speed almost immediately.

That means that after an upshift, with the rpm down around 1,000 or 1,100 rpm, the engine comes up to 90 percent of peak torque before the hammer is halfway to the floor.

The Chelsea test track has a few steep grades to play on, so we ran the DD15 up a seven-percent grade at 30 mph. That was no challenge at all, so I took a second pass, deciding to try an upshift on the hill. From a near-stop at the bottom of the hill in fourth gear, I made my way up through two gears before cresting the hill. The DD15 was still powering up the hill at as low as 900 rpm.

Out in the real world the following day, I headed north to Saganaw, and over the Zilwaukee Bridge. At four percent, it’s not much of a grade, but it’s the only substantial grade within 250 miles of Detroit. I hit the hill on the first pass at cruise speed (60 mph, 1,300 rpm) and dropped only 5 mph at the top. On my second pass, I hit the hill at 50 mph (1,000 rpm), and the engine dropped only 2 mph going over the top. It drifted down to 950 rpm and stayed there all the way up.

Everyday Driving:

Cruising at highway speeds, the foot feed is very responsive at any point in the useable engine speed range. The turbo reacts almost instantly, giving the truck an almost automotive feel.

At the low engine and road speeds of an urban environment, shifting becomes much less of a challenge than I’ve found with some VGT engines. You just don’t need any more than 1,000-to-1,200 rpm in any gear short of eighth and up, so you don’t have the torquey shifts and finicky pedal response common to some VGT engines.

I can say, though, that the fuel usage meter was working, and I monitored the fuel through-put over a 31-minute period. The meter showed exactly four gallons consumed. That’s four gallons over 30 minutes/miles, or 7.75 mpg at 65,000 lb GVW.

I predict this engine will be very well received by drivers, mechanics, and fleet owners alike. There’s a lot to like about the thing, and if the B50-life and the extended maintenance intervals live up to the billing, this will be an engine the market is ready for.

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