Daimler Trucks is the largest truck manufacturer in the world, having sold some 329,800 vehicles in 2008 and claiming a 15.2% slice of the global truck market. So when the company launches a new range of engines, it’s big news in every sense.
It was 2002 when the Daimler Trucks division began developing a new family of inline six-cylinder engines referred to as the Heavy Duty Engine Platform (HDEP). The new engines would replace the various families of engines powering its Freightliner, Mercedes-Benz, Mitsubishi Fuso, Western Star, and Thomas Built Buses vehicles. The company closed its Sterling Trucks operation early in 2009; the division, formerly Ford’s heavy-truck operation, was purchased in 1995.
Daimler stated that the HDEP engine family would consist of three engines, replacing the Detroit Diesel Series 60 and MBE 4000 series engines in North America, the V6 and V8 engine families and MBE 4000 derivative in Europe, and the Fuso truck engines in Japan. The new engines have been jointly developed in Europe, the U.S., and Japan.
Truck engine development around the world dances to the tune of the global emissions rounds, and replacing Daimler’s disparate truck engine families with a common platform will bring obvious cost reductions and replace engines that are approaching the end of their lives.
North America has been the first to receive the new engines, with the last and largest arriving earlier in 2009. The Detroit Diesel DD16 is a 15.6-L engine, following on from the 14.8-L DD15 variant announced at the end of 2007 and the 12.8-L DD13 variant that arrived the following year. Effectively, the DD16 is a longer-stroke version of the 14.8-L unit. All variants are certified to the forthcoming U.S. EPA 2010 emissions limits.
The DD16 is available in nine power ratings between 475 and 600 hp (354 and 448 kW) with torque spanning the 2373 to 2779 N·m (1750 to 2050 lb·ft) range at 1100 rpm. As with the other HDEP engines, the DD16 features several innovative technologies. While it is not the first heavy diesel engine to use turbo-compounding, there are still relatively few automotive applications with this technology. In the case of the HDEP engines, power is fed from a second turbine to the flywheel via gear sets and a hydraulic coupling, recovering energy that would otherwise be dissipated as heat in the exhaust gases.
Although other manufacturers have used amplifying piston systems to raise fuel pressure before, notably Caterpillar with its Hydraulic Electronic Unit Injector (HEUI) system in the 1990s, further applications have been rare in recent years. Daimler is certainly among the first to use the technology in a common-rail system.
For the DD13, 15, and 16, the system enables rail pressure to be kept relatively low at around 900 bar (13,000 psi), with the double-ended amplifying piston positioned close to the injector to raise injection pressure to around 2200 bar (32,000 psi). The lower pressure fuel acts on the end of the piston with a larger surface area, further compressing the fuel at the other end of the piston with its smaller surface area, which has the effect of “amplifying” the pressure in direct proportion to the relative surface areas of the piston faces. Potentially the system could yield higher pressures by altering the relative surface areas of the two ends of the piston.