8- and 12- cylinder engines for use in on-road, off-road and maritime applications as well as power generation
One base engine - multiple applications
MAN makes specific adaptations possible for different requirements.
The most important criteria are powerful acceleration, wide torque range, and low weight.
Low heights, narrow spaces, and very long operating times determine the requirements on the engine.
Different operating types, materials, and locations form the focus of engine modifications for power generation.
The safety of passengers and the crew as well as numerous legal requirements determine the design of the engine.
A MAN base engine - various applications
Engines are operated in a great variety of applications, each of which imposes completely different specific requirements on the engine. In the D2862/68 V-engine series developed by MAN, 8- and 12-cylinder engines have successfully been brought to market in road vehicles, agricultural machinery, trains, yachts and working vessels as well as for power generation in the form of diesel- and gas-powered units. The various requirements for the different applications will be described and shown in the following, as well as how these influences have been taken into account in the design of the base engine and how engines for the different applications were made with as many identical parts as possible.
A family of V-engines was to be developed at MAN for operation in various, completely different applications. At MAN, the applications fall into four areas:
On-Road for vehicles operating exclusively on roads, such as trucks
Off-Road for operation in the agricultural sector, the construction sector and railways, in locomotives and railcars
Marine for operation in yachts and working vessels
Power generation for engines used in gensets
Arising from its application, the engine is subject to radically different utilisations at different power outputs. For example, the maximum annual operating time in some applications is only 1,000 hours with a maximum of 20% thereof at full load, while other applications call for unrestricted operating time under 100% full load.
Moreover, different applications are governed by completely different legislation on exhaust emissions, ranging from the Euro V / EEV standard to various EPA and IMO regulations to the Technical Instructions on Air Quality Control.
In order to cover the widest possible power-output spectrum within the various applications, the family of engines was to be realised as 8- and 12-cylinder variants. To expand the range of operation of the engine family even further, it was to be possible to run the engines not only on diesel fuel but also on natural gas and biogas.
MAN understands the base engine as being the scope of parts identical to all applications. Essentially, this is the engine itself, comprising:
crankcase and fly-wheel housing
crankshaft and camshaft
cylinder head and cover, incl. rocker arms, valves and so on
oil cooler, separator and filter
injection system incl. rail injector, high-pressure pump
The development goal with respect to the base engine is the largest possible scope of identical components in order to create a fully-developed basis for the rapid and secure realisation of new applications. The base engine for the D2868/62 is a joint development with Liebherr Machines Bulles SA.
The base engine was initially designed for the highest rated power. This is the yacht engine with two-stage turbocharging, with peak pressures above 240 bar and an average pressure of almost 29 bar. All the components of the engine must be capable of safely withstanding the combustion forces occurring here for the duration of service life.
The combustion design was similarly conducted for this power variant. Engines with lower power outputs may have significantly longer operating times. For this reason, complementing the above-mentioned approach every component of the engine has to be tested for durability over the longest service life (at lower forces in some cases).
Independent thereof, tests for checking the overall engine system are mandatory for every application. The engine developed was one with a 90° cylinder-bank angle, a capacity of two litres per cylinder with a 128 mm bore and 157 mm stroke, the camshaft mounted below and four valves per cylinder.
The engine has individual cylinder heads to increase its variability with regard to the number of cylinders. In order to comply with the exhaust-gas standards laid down for various applications, a common-rail injection system was selected so that high injection pressures would be achieved.
Due to the high gas forces occurring at high power outputs, the crankshaft is not secured on the main bearings by means of bearing caps but - unusual for an engine of this size - by means of a bedplate. The great rigidity of the bedplate and the optimisation of its bolting to the crankcase guarantees the secure seating of the crankshaft even at the highest outputs.
Every application imposes different requirements on the base engine and the engine periphery. These were taken into consideration during the design of the base engine.
Engines for purely on-road vehicles are also subject to special requirements. Installation space in conventional tractors is very limited. These vehicles are usually fitted with six-cylinder in-line engines, a design type which is inherently more compact.
In addition to a wide torque range and powerful acceleration, a decisive design criterion is primarily low engine weight.
Engines for off-road applications often have to be integrated into existing engine compartments. These vary radically, depending on the application. Many railway applications require engines of a very low design height. It is quite possible that this packaging restriction will influence the design of the base engine. Because of cramped installation spaces, especially in agricultural machinery, particular attention must be paid to the transfer points of exhaust gas and charge air. The load on the engine also varies, depending on the application.
In the case of railway engines, high thermal loads can occur. These result from the typical manner in which a regional train operates: the train accelerates away from the station, reaches its normal operating speed, brakes on reaching the next station and so on, in continual repetition.
For agricultural machinery, the engine has to be designed with a rising torque characteristic so that the machine can be driven into the crop to be harvested or the material to be chopped and still have adequate torque available at decreasing engine speed when it commences the process.
Some of the other requirements of off-road applications are very often long operating times, operation in very dusty environments (forage harvesters, for example) and the high vibration loads due to non-elastic engine mountings. Besides operation in agricultural machinery and trains as already mentioned, off-road engines are in addition used to operate construction machinery, also through the cooperation with Liebherr. These engines deliver between 545 and 680 hp in the V8 versions, while the V12 versions deliver between 800 and 1,200 hp.
Engines for power generation are generally deployed to provide continuous power (COP), to cope with peak loads (PRP: prime power) or as emergency power-supply units (LTP: limited time running power und ESP: Emergency Standby Power). Depending on the type of operation, the output and the permissible annual operating times differ: for example, 50 hours per annum for emergency power-supply units, up to 24 hours a day for continuous power. Gensets consist of an engine with combination coolers for cooling charge air and coolant fitted in front and a flanged-on generator.
All engines used for power generation are operated at a constant speed: 1,800 rpm for 60 Hz, 1,500 rpm for 50 Hz AC voltage. In addition, operation with a flanged-on generator results in further loads on the engine. For example, the crankshaft supports the generator shaft, a factor that has to be taken into account in the crankshaft design and the calculation of torsional vibration.
Furthermore, in regulating the frequency of the genset overall, flanged-on generators can also transmit fluctuations in the electricity network to the engine in the form of torque shocks, which have to be withstood. Depending on the installation site of the unit, environmental loads may also arise. Such engines sometimes have only slight protection in dusty regions (deserts) or operate at great geodetic altitudes over 4,000 metres where the oxygen content of the air is low.
The engine is designed to run not only on diesel fuel but also on natural gas and biogas. This engine is available in turbocharged versions delivering up to 580 kW and as an economical aspirated version delivering 270 kW. A separate cylinder head, piston and cylinder liner have been developed for operation with gas. The remaining components are identical with those of the diesel-powered engine. By comparison, the V12 variants of the diesel engines deliver between 700 and 1,117 kW.
Marine engines are characterised by the special installation situation on board vessels, where they are cooled with sea water. In the case of the engine under discussion, sea water cools the charge air directly, subsequently cooling the engine coolant via a plate-type heat exchanger.
Furthermore, complex measures are necessary to comply with the statutory regulations concerning maritime vessels. The International Convention for the Safety of Life at Sea (SOLAS) stipulates amongst other things that the maximum permissible surface temperature of an engine is 220°C.
To achieve this, a water-cooled exhaust system was installed in which the high-temperature resistant parts conducting the exhaust gas (exhaust pipe, turbocharger) are insulated by an air space through water-cooled, double-walled aluminium jackets. Operation on working vessels is often subject to additional regulations laid down by classification societies such as German Lloyd, for example.
The objective is always the safety of passengers and crew. For this reason, engines must be equipped inter alia with redundant sensors and double-walled fuel-injection lines. Switchable oil and fuel filters must enable filters to be replaced during operation. Dispensing with the use of hoses as far as possible and avoiding materials, such as aluminium in areas that come into contact with fuel, aim at increasing resistance to fire.
Engines in the marine sector are similarly subjected to very different loads. Operation on yachts is characterised by very high performance and the demand for rapid acceleration coupled, however, with low annual operating times. To achieve the highest power rating, the engine is fitted with two-stage turbocharging and intercooler (two turbochargers per cylinder bank).
By comparison, the working-vessel sector requires rugged engines that provide long operating times at low power. Typical working vessels are, for example, barges, passenger ferries, pilot boats, fishing boats, day cruisers, patrol boats and so on. All these boats are fitted with twin-engine systems at a minimum, i.e. two engines per vessel.
Individual solutions for large-volume production
All application-specific requirements were taken into consideration in the design of the base engine. The design objective was to be able to realise many different versions of the engine with a large number of identical components. At part-number level, approximately 450 identical components can be used across all applications. Given an approximate total number of 1,150 components in an on-road engine and 1,950 in a marine engine, this is around 25 to 40 percent.
Thanks to the consistent pursuit of individual requirements, it has been possible to find economical solutions even for low-volume applications, thus avoiding the cost of subsequent modifications. For example, installation space and attachment points for supplementary sensors for classified marine engines were provided right from the start, so that they were then able to be integrated in engine components without effort or cost.
During design, individual requirements of the applications often appear to conflict with one another. Thus durability at high rated power (and the accompanying high gas forces) conflicts with the requirement that the low-power engine should weigh as little as possible. In order to be able to utilise identical components sensibly despite this, many important components were optimised. For example, the bedplate design led to a rugged and highly rigid structure that also has advantages for low-powered engines.
However, in various areas identical components were consciously relinquished.
In order to be able to realise the various application-specific torque curves and power outputs sensibly, pistons with different surface finishing and compression as well as adapted valves are employed.
In addition to mainly software variations in fuel injection and the turbocharger design, the efficiency of individual engines can in this way be significantly enhanced. An example here is the oil pump, where gear teeth of a different width are used for different volumes of oil.
Taking into account the naturally low annual volume of engines in the 16- to 24-litre class, the identical-component strategy is a cost-saving one. For one thing, the number of parts is smaller, reducing warehousing costs, and for another, volumes per part are higher.
However, by far the greater benefit derives from having a fully developed base engine that can be used as the basis for the rapid and secure development of new variants for various applications, thus enabling the realisation of a wide range of applications with robust and successful engines.
With the MAN D2868/62 V-engine series it has proven successful to derive specific engines for various different applications from a single base engine, using a large number of identical components.
For on-road use: compact installation space as small 6-cylinder engines are normally used, higher engine weight means lower cargo
Railway: low height e.g. underfloor or roof-mounted, high cycling of the thermal load as the train accelerates away fast from a station, reaches its normal operating or rolling speed and brakes upon reaching the next station
Agricultural machinery: narrow installation spaces, use in very dusty environments, rising torque characteristic for comparable performance when moving amongst crops, high vibration loads due to non-elastic engine mountings
Emergency power generators: annual operating time of 50 hours per year with overload
Continuous power generator: 24-hours daily. Load on the engine due to flanged-on generator, pollution due to the environment (deserts, mountains)
Working vessels: robustness with long operating times at lower power, narrower installation space, cooling with seawater, safety regulations for operation and for insurance through classification organisations such as the German one, Lloyd (redundant sensors, double-walled fuel injection lines, fire-resistant materials)
Yachts: very high performance with rapid acceleration coupled with low annual operating times