8- and 12-cylinder engines for on-road, off-road and maritime applications as well as in power generation
Engines are used in a broad range of applications. And each application places very different specific demands on the motor. With the V-engine series D2868/D2862 developed at MAN from 2011 onwards, 8- and 12-cylinder engines in road vehicles, agricultural machinery, trains, yachts, workboats and for power generation as diesel and gas gensets have continuously been launched on the market with great success.
In the following, the different requirements of various applications are described. It is shown how these specifications have influenced the base engine design and how engines could be realised with as many parts in common as possible despite the wide variety of uses.
Today’s current product portfolio may in part differ significantly from products and performance ranges mentioned in the article due to further developments and current exhaust gas legislation.
The development goal was to create an MAN V-engine family that could be used in a wide variety of applications. At MAN, four application areas are differentiated:
Depending on the application, different performance levels result in completely different load capacities for the engine.
For example, there are applications with a maximum utilisation of only 1,000 hours per year and a maximum full-load share of 20 % as well as applications with unrestricted running time under 100 % full load.
Furthermore, different applications are subject to very different exhaust gas regulations, ranging from the then current Euro 5/EEV standard (2012–2016) to various EPA and IMO requirements and the TA Luft.
To cover the widest possible power spectrum within the various applications, the engine family was to be realised as 8-cylinder and 12-cylinder engines. In order to further expand the range of applications of the engine family, it should be able to run on natural gas and biogas in addition to diesel.
At MAN, the base engine is understood to be the range of parts that is identical between all applications. This essentially comprises the actual power unit, consisting of:
The aim of base engine development is to keep the scope of common parts as large as possible across all applications in order to create a fully developed basis on which new applications can be realised quickly and safely. For the D2868/2862, this base engine is a joint development with Liebherr Machines Bulles SA.
The base engine is initially designed for highest output. This means for the two-stage supercharged yacht engine peak pressures above 240 bar and an intermediate pressure of almost 29 bar. All engine components must be able to safely withstand the combustion forces that occur here over the entire service life.
The combustion design is also initially carried out for this power variant. Significantly higher running times can occur for engines with lower power. This means that in addition to the above approach, the design of each engine component must therefore be checked for durability over the longest possible service life (partly with adapted reduced output).
Independently of the aforementioned, tests to check the overall engine system of each application are mandatory. The result is an engine with a 90 ° bank angle, a displacement of 2 l per cylinder with 128 mm bore and 157 mm stroke, a bottom-mounted camshaft and four valves per cylinder.
For high variability in the number of cylinders, the engine is equipped with single cylinder heads. In order to meet the exhaust emission standards of various applications and to achieve high injection pressures, a common rail injection system was chosen.
Due to the high gas forces occurring at high loads, the crankshaft is not bolted to the main bearings with individual bearing covers, but – unusual for this engine size – via a crankcase bottom section (the so-called bedplate). Due to the high rigidity of the bedplate and the optimised bolting against the crankcase, secure bearing of the crankshaft is guaranteed even at the highest loads.
When designing the base engine, the specific requirements of the respective application were taken into account.
This also applies to on-road vehicles. In classic tractors, for example, the installation space is very tight since they are often equipped with more compact 6-cylinder engines.
In addition to the wide torque range and powerful acceleration, a low engine weight is a decisive design criterion, as it is directly reflected in an increased payload.
Off-road engines often have to be integrated into existing engine compartments. These vary greatly depending on the application. For many railway applications, engines must be designed with a very low overall height. This packaging restriction may well have an influence on the design of the base engine. Due to the tight installation spaces, especially in agricultural machinery, special attention must be paid to the transfer points of exhaust gas and charge air. The engine load also varies depending on the application.
In railway engines, high thermal shock loads can occur. These result from the typical operation of regional trains: Starting the train at the station with strong acceleration, rolling, braking when reaching the next station – all that in constant repetition.
In the agricultural machinery sector, the engine must feature an increasing torque characteristic to be able to drive into the harvested or shredded material at overspeed and have sufficient torque available at the start of processing when the speed drops.
Some other off-road application requirements comprise extremely high running times, use in very dusty environments (such as in forage harvesters) and high vibration loads due to non-elastic engine mounts.
In addition to the aforementioned applications in agricultural machinery and trains, off-road engines are also used in construction machinery. Engine power ranges from 401 kW to 500 kW (545 HP to 680 HP) for the V8 and 588 kW to 883 kW (800 HP to 1200 HP) for the V12.
Engines for power generation are used either as continuous power generators (COP: Continuous Power), for peak load coverage (PRP: Prime Power) or as an emergency generator (LTP: Limited Time Running Power and ESP: Emergency Standby Power).
Depending on the operating mode, the power and the permissible annual operating time differ as follows: 50 hours p.a. for emergency generators, unlimited up to 24 hours per day for continuous generators.
Gensets usually consist of the engine with a pre-installed combination radiator for charge air and coolant cooling and a flange-mounted alternator.
All engines for power generation are operated at constant speed: 1,800 rpm for 60 Hz, 1,500 rpm for 50 Hz AC voltage. When operating with a flanged alternator, further loads occur on the engine. The generator shaft is supported on the crankshaft, which must be taken into account in the crankshaft design and the torsional vibration calculation.
In addition, due to the frequency control of the entire genset, fluctuations in the power grid can be passed on to the motor as torque surges. The place of use must also be taken into account. Engines are sometimes used with little protection in dusty environments such as the desert, or at high geodetic altitudes of up to 4,000 m with low air oxygen content.
In addition to diesel operation, the engine is also designed for operation with natural gas and biogas. This engine is available with outputs from 270 kW to 580 kW. A separate cylinder head, piston and cylinder liner were developed for operation with gas. The remaining engine parts are identical to those of the diesel engine. By comparison: Diesel units as V12 engines have outputs of 700 to 1,117 kW.
Marine engines are characterised by the special installation situation on ships. For example, marine engines are cooled with seawater. Cooling is initially provided directly by the charge air, then via a plate-type heat exchanger using engine coolant.
In addition, elaborate measures are necessary to comply with the applicable legal regulations on ships. The “International Convention for the Safety of Life at Sea (SOLAS)” requires, among other things, a maximum surface temperature of 220 °C for the engine.
For this purpose, a water-cooled exhaust system was installed, in which the high-temperature-resistant exhaust gas-carrying components (exhaust pipe, turbocharger) are insulated via an air gap by water-cooled, double-walled aluminium shells. For use on workboats, further regulations of so-called classification societies, such as the Germanische Lloyd, apply. Workboats can often only be operated or even insured after acceptance by one of these companies.
The aim is always the safety of passengers and crew on board. For example, engines must be equipped with redundant sensors and double-walled injection lines. Avoiding the use of hoses and certain materials, such as aluminium in the fuel area, where possible is intended to increase fire resistance.
Engines in marine applications are also subjected to very different loads. Use on yachts is characterised by the demand for very high performance and acceleration values, albeit with low annual running times. For the highest performance levels, the engine is equipped with two-stage turbocharging with intercooler (two turbochargers per bank).
In the workboat sector, on the other hand, robust engines with long running times at lower outputs are required. Typical workboats are e.g. pushboats and barges, passenger ferries, pilot boats, fishing cutters, excursion boats, and patrol boats. All these boats are equipped with at least twin engine systems (two engines per vessel).
All application-specific requirements have been taken into account in the design of the base engine. At part number level, approximately 450 common parts could be used across all applications. With a total number of about 1,150 parts for an on-road engine and about 1,950 parts for a marine engine, this corresponds to a percentage of about 25 to 40 percent.
By consistently following the individual requirements, it was possible to find cost-effective solutions even for applications with lower quantities and to avoid later modification costs. For example, the installation space and connection points for additional sensors on classified marine engines were provided from the outset, so that they could be integrated on engine components without effort or cost.
Often, individual requirements of the applications appear contradictory during the design. For example, durability at high power levels (and the associated high gas forces) conflicts with the demand for the lowest possible weight in low-power engines. In order to still be able to use common parts sensibly, a large number of significant components were optimised. For example, the bedplate design has resulted in a robust and very rigid construction, which also has advantages for low-power engines.
In various areas, however, common parts were deliberately omitted. In order to be able to reasonably reproduce the various application-specific torque curves and power outputs, pistons with different grinding patterns and different compression as well as adapted valves are used.
This means that, in addition to mainly software variations in injection and turbocharger design, the efficiency of the individual engines can be significantly increased.
For different delivery rates, different gear widths are used on both the oil pump and the coolant pump.
Taking into account the naturally rather low annual quantities of engines in the 16 to 24 litre displacement class, the common parts strategy offers cost advantages – on the one hand through the lower number of parts in itself (e.g. in the area of warehousing), on the other hand also through higher quantities per component.
The far greater advantage, however, is that a fully developed base engine has been created, which makes it possible to derive new variants for various applications quickly and safely. This generates a broad application portfolio with robust and successful engines.
With the MAN V engine series D2868/D2862, it has been possible to derive specific engines for the most varied applications from just one base engine using a large number of common parts.