Compact and powerful: MAN’s 9-litre diesel engine for off-highway applications
Furthermore, great attention was paid to the modularity of the 9-litre engine kit. The following illustration shows the different variants in trucks, buses and as CNG and tractor engines.
The versions differ, for example, in fan attachments and belt drives, cylinder head covers and oil pans made of plastic and aluminium, and turbochargers with wastegate or VTG. Unlike its diesel counterpart, the E1856 natural gas version is equipped with cooled exhaust gas recirculation (EGR). The bus version can be supplied with an optional crankshaft starter alternator.
The development (see following table for technical data) and integration of the D1556 into the tractor is described in detail below.
SCR catalytic converter
The dimensions of the predecessor model also had to be adopted for the exhaust piping and urea treatment.
The SCR was already designed in 13” – the largest commercially available standard diameter for cordierite substrates – in the previous version of the vehicle. Only the extension of the SCR substrates was able to meet the higher requirements for exhaust gas mass flow and NOX conversion. The flow uniformity distribution on the SCR inlet had to be increased to a Uniformity Index of at least 0.98. In order to achieve the requirements regarding uniform distribution and exhaust backpressure, various optimisation loops at different operating points were calculated by simulation. The target variant was checked during validation on the hot gas test bench with regard to flow and NH3 uniform distribution and the simulation results were confirmed.
The exhaust gas aftertreatment system was subjected to targeted low-load testing at the Nuremberg engine plant. For this purpose, a tractor from Internal Logistics was used. The tractor was equipped with a data logger. At regular intervals, the deposit tendency of the AdBlue® mixer was checked by means of an endoscope (see Fig. 6) and the loading of the DPF was determined by weighing.
Figure 7 clearly shows the low load of commuter traffic. Based on the findings, it was possible to adapt the application accordingly. The proximity of the test vehicle to the development department substantially facilitated the process.
Endurance testing
For endurance testing, the testing method is also based on testing the engine in trucks and buses. In total, the new D1556 engine has accumulated over 200,000 hours on a wide variety of test benches. Approx. 10 % of this were used for the off-road application (see Fig. 8).
In-vehicle testing constituted also an important cornerstone for validation. Additionally, the engine accumulated a comparable number of test hours in the tractor. In the course of development, more than 20 tractors were validated for this purpose under the toughest conditions (see Fig. 9).
When selecting the correct continuous operation programme, a preliminary comparison was made between actually measured field cycles and internal continuous operation cycles.
When creating the test programme, real-life use cases were specifically examined and evaluated with regard to various criteria.
Among others, the following criteria were used for the assessment:
- Work over runtime (average engine load)
- Average speed (number of load cycles)
- Thermo-mechanical damage, example exhaust manifold
- Switching cycles of the mechatronic components
Figure 10 compares the measured field cycles with the test run cycles.
If we look at the number of load cycles and the average engine load over runtime (e.g. 8,000 h), it becomes clear that it is almost impossible to check this within a continuous run. In contrast, the thermo-mechanical damage is sufficiently well represented by generic cycles. In contrast, the endurance cycles were not optimised with regard to the dynamic load of the actuators, as these are checked by component tests.
Challenges and difficulties in off-road use
Unlike measurements of cars or trucks, off-road use poses far-reaching challenges and difficulties for which the mobile exhaust gas measuring equipment had to be prepared.
Thus, the PEMS system had to be designed in a modular way so that it could be mounted individually on every machine in the off-road sector. While the installation of the measuring equipment for tractors is simple, additional space had to be created for the measurement in harvesters within the legal maximum dimensions of a vehicle in order to be able to install the mobile measuring equipment.
In this way, it was possible to prevent the legal 1 % rule from being violated and to avoid cross-influences on the emission measurement caused by exhaust gases from the genset. The power supply was implemented using a battery pack tailored to the needs of the measuring equipment, which guaranteed measurement operation for at least one day and could be recharged overnight. Further difficulties were the encapsulation of the measuring equipment in order to be able to completely exclude influences by dust (e.g. harvest dust) or moisture and splash water. In addition, a measuring device that measures recirculated air independently via synthetic air was used for exhaust gas emission analysis. Appropriate cooling of the measuring technology also had to be ensured, as the maximum measuring device temperature of 40° C can quickly be exceeded, especially during measurements in summer harvesting operations.
Figure 12 shows the installation of the PEMS measuring technology on the front hydraulics of a tractor, where all the previously mentioned points were taken into account to ensure stable measurement of the tailpipe emissions.
In addition, the PEMS measuring tube is insulated to prevent excessive surface temperatures and thermal incidents during harvesting.
One of the biggest differences to on-road applications is the dependence on weather and harvest windows. For example, tractors can only carry out their work in arable farming under certain conditions and harvesters work only during the harvest season in Europe. This means that sometimes only short time windows are available to carry out the PEMS measurements.
Measurements and results
The length of the measurement varies greatly to achieve the legally required length of five to seven times the cycle work of an NRTC. For example, the measurement can take only about one hour for high-load work, and up to 3.5 hours for low-load applications. Since the cold start is not yet a fixed part of the ISM measurements, several measurements can be carried out during the day.
In the course of the ISM measurements already carried out on various vehicles during a wide range of operations, it has been shown that there is a large variance in the results of the CF factors determined, depending on the load and type of operation of the vehicle. However, it can be proven that results from the engine test bench are reproducible in operation under real conditions and that CF factors <1 are also possible in high-load applications such as ploughing with a tractor.