Compact and powerful: the 9-liter diesel engine from MAN for off-highway applications
In 2019, MAN launched a newly developed engine with a displacement of 9 liters. In addition to traditional applications for trucks and coaches, the industrial version has been presented at the same time. For its first application in the off-highway segment, the engine is used in agricultural tractors, where SCR-only combustion and exhaust gas aftertreatment have been completely revised and adapted. The low-speed concept and excellent engine dynamics were of particular importance. A large number of field cycles were analyzed during testing and the test program was adapted to the tough conditions in the tractor. Moreover, this report presents activities and results for recording the tractor’s Real Driving Emission in a wide range of applications.
A few years ago, MAN decided to start developing the new D15 engine platform, bridging the gap between the 7-liter and 12-liter displacement class. During the development process, the main objectives included a low power-to-weight ratio and compact dimensions. The straight-six power unit delivers between 205 and 324 kW (279 and 440 HP) and its highest power variant achieves a maximum torque of 1970 Nm between 1150 and 1300 rpm (see Fig. 1, on the left). This makes the MAN D1556 the lightest off-road engine in its displacement class, with a dry weight of just 860 kg. Even at low speeds, it delivers an impressively high torque.
In its first application as an industrial engine, the new D1556 engine is used in tractors where, due to space restrictions and high utilization, it has a maximum output of 305 kW. In order to serve the global market, the engine has been certified for emission stages EU Stage V, EPA Tier 4 Final, and EU Stage IIIa for Low Regulated Countries.
The following figure shows the current state of the power curve in tractors. A competitive comparison (see Fig. 1, on the right) clearly shows that the D15 is in a leading position – particularly at maximum torque.
The variants differ, for example, in fan attachments and belt drives, cylinder head covers, and oil sumps made of plastic and aluminum, as well as turbo chargers with wastegate or Variable Turbine Geometry (VTG). In contrast to its diesel counterpart, the E1856 natural gas variant features cooled exhaust gas recirculation (EGR). The coach variant can be supplied with a crankshaft starter alternator as an option.
The following section describes in detail the development (see the following table for technical data) and integration of the D15 into tractors.
Technical data – tractor engine
|Engine type||D1556 LE5xx|
|Exhaust gas status||EU Stage V, US EPA Tier 4 final, Downgrade UN-ECE
R96, H (complies with EU Stage IIIA)
|Number of cylinders/arrangement/valve s per cylinder||6/inline/4|
|Injection/ignition pressure [bar]||2,500/230|
|Weight (dry) [kg]||Approx. 860 (without exhaust gas aftertreatment), approx. 960 (with exhaust gas aftertreatment)|
|Rated power [kW] at speed [rpm]||217||239||261||283||305|
|Max. torque [Nm]||1,550||1,650||1,750||1,850||1,970|
|at speed [rpm]||1,100–1,300||1,100–1,350||1,100–1,400||1,150–1,400||1,200–1,350|