DAF unveiled a raft of new products at the U.K. Commercial Vehicle Show in April, from the new 10.8-L Paccar MX-11 diesel engine that will power trucks in the DAF, Kenworth, and Peterbilt ranges, to the revised LF light truck and CF heavy truck ranges. DAF will be the first Paccar company to use the new MX-11 engine from fall 2013, while Kenworth and Peterbilt are expected to offer the MX-11 from 2015.
The engine shares a number of design characteristics with the larger 13-L Paccar MX-13 engine, such as a single-piece cylinder head and construction in compact graphite iron (CGI). The cylinder head itself features two overhead camshafts driving four valves-per-cylinder. High-pressure common-rail fuel injection is used, so the camshafts do not have to drive high-pressure injectors. As a result, the camshafts are a hollow design. This feature and the use of a separate fuel-injection equipment camshaft are said to reduce weight by 15 kg (33 lb).
The fuel-injection system is common to both the MX-11 and MX-13 engines, although each engine carries its own software calibration.
“We have always been focused on fuel economy,” explained Ron Borsboom, member of the DAF Trucks Board of Management responsible for Product Development. “We will be focusing on fuel economy even more and market forces will drive us in that direction. There will be some push from the legislators as well, so we really did some thinking about how do we get the answer to a next step in fuel economy; a downsized engine is an important element. There are certain limits to that, but in the range between say 350 hp and 450 hp there was a clear opportunity of defining a new engine concept based on the downsizing principle that brings certain benefits.
“If you go with slightly smaller dimensions, you open up opportunities for weight saving, you open up opportunities for more clever solutions—less parasitic losses and the better utilization of the iron and all the materials in the engine. If you run the engine at the same average duty cycle as a larger engine, it has somewhat higher BMEPs [brake mean effective pressures] and the design is based on those higher BMEPs; that’s why, for example, this engine has a double overhead cam.”
The common-rail injection system runs at injection pressures up to 2500 bar (36.3 ksi) and can offer pre- and post-injection or a combination of both.
“Our philosophy for common rail is to not have a separate common-rail pump on the outside of the engine but to build that common-rail pump functionality more or less integrated in the engine block,” said Borsboom. “So there’s a small camshaft with multiple lobes that drives two fuel pumps that are integrated in the engine block and they feed the common rail.”
Integrated design is also applied to the cylinder head, where the air intake manifold is part of the head architecture.
An engine brake is included in the MX-11 design and when applied, only one camshaft is actuated to reduce the gas flow and increase the level of backpressure on the piston.
“That sits within the whole strategy,” explained Borsboom. “Firing the engine is something you can control and get the right power and torque, but if you don’t take extra measures, the engine braking power is just a function of the swept volume. Since swept volume is a bit smaller, we had to come up with something that boosted the brake torque above the level of your normal 11-L engine.”
The engine brake delivers up to 320 kW (429 hp) of braking power, and over 70% of that total is delivered at 1500 rpm.
Other design features include a variable-geometry turbocharger and exhaust gas recirculation (EGR), which is the initial means of emission control, combined with selective catalytic reduction (SCR). DAF says that the particulate filter cleaning intervals can extend up to 500,000 km (310,685 mi). The engine is equipped with a single poly V-belt and the cooling fan mounted directly on the end of the crankshaft.
The water pump features a two-speed electromagnetic coupling to improve efficiency, while the air compressor for the braking circuits is designed to operate as much as possible during deceleration to minimize fuel consumption. Wiring harnesses are encapsulated, and the alternator and air-conditioning compressor are mounted on the engine as a single unit.
The engine will be offered with five power outputs: 210 kW (282 hp), 240 kW (322 hp), 271 kW (363 hp), 291 kW (390 hp), and 320 kW (429 hp). The highest two ratings are designed for long-haul and heavy-duty applications, while the lower ratings are aimed at urban, regional, and national operations.
The engine will be used in both the new DAF CF medium/heavy-duty truck and XF long-haul truck. DAF suggests that fuel consumption is on average about 3% lower than the 13-L MX-13 engine, and the MX-11 weighs around 180 kg (397 lb) less.