COVER You STORY Marine Engines will find the figures mentioned in this article in the German issue of MTZ 3/2004 beginning on page 160.
Der neue Schiffsmotor der MTU-Baureihe 2000
The New MTU Series 2000 Marine Engine Engines for fast ships have always been a competence of MTU Friedrichshafen. With the new series 2000 CR the company is now continuing this tradition. The engines in this series use state-of-the-art technologies so they are more powerful, more economical and cleaner than the preceding 2000 series. The basic concept, charging, injection, and electronics have been redesigned. Use of the common rail injection system has given the series its name of 2000 CR.
1 Introduction
By Werner Kasper, Hermann Baumann, Michael Willmann, Günther Schmidt, Volker Wachter and Jörg Remele
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The aim of developing series 2000 CR was to replace the existing products completely with the new marine engines and thereby satisfy the emission directives and the customers' demand for higher power density. The new series 2000 CR, Figure 1, meets the requirements made of it: The power range was expanded in order to link up to the power class of the series 4000. The series is being extended to include a 10-cylinder version in order to fill the power gap between 8V and 12V. The bulk volume and power-toweight ratio were optimized by increasing the power-per-cylinder capacity ratio. In this way it is now possible to provide the power of a 12-cylinder engine from the previous series with a 10V engine of the new model. The power of the new 16-cylinder engine will seamlessly link up to that of the 4000 series.
The required low power-weight ratio for the engines was not solely achieved by raising cylinder capacity and systematic use of light alloy. A major role was also played by the modular design of the engine, integration of several functions in one and the same component, and weight optimization of the components with the aid of analysis. The new series meets the customers' demand for compactness and “clear-cut lines” without compromising ease of maintenance or the option of attaching peripheral units. On the contrary, in terms of easy maintenance it has been possible to achieve substantial improvements. The interfaces at the engine and the “footprint” were designed in such a way that with a matching transmission it is possible to use the new engine instead of the previous one at no extra cost. The engines of the new series meet the emission specifications of IMO and EPA
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COVER STORY
TIER 2, they guarantee the Solas-specified surface temperatures of less than 220°C, and meet the requirement that seals on components carrying combustible liquids be shielded. 2 Achievement of Development Targets
Further development of the series must not only take account of the stringent requirement profile of the 1B application (ships in continuous duty) but also yacht builders' demand for a highly compact, lightweight engine. At the same time all the relevant emission requirements had to be observed. For this reason, in addition to using stateof-the-art technologies for charging, injection and electronics, the engine concept had to be revised. Cylinder capacity had to be increased from 1.99 l to 2.23 l (bore 156 mm / stroke 135 mm, Figure 2). The engine speed potential (2450 rpm + 50) was matched to the customary maximum rotational speed of appropriate transmissions. Mean effective pressure was increased moderately and peak pressure was also raised in order to achieve good levels of fuel consumption. 2.1 Basic Engine Concept
By using common rail injection technology it was possible in the engine vee to dispense with the unit pumps used to date on series 2000 engines. Consequently, the crankcase was redesigned fundamentally. For low oil consumption and low ring and liner wear it is absolutely essential to reduce liner deformation to a minimum. In several optimization stages the water feed and return ducts in the engine vee were designed as box-type structures that strengthen the cylinder walls and brace the cylinder banks against one another. Another focus of attention in optimizing the crankcase was the crankshaft bearing. With as little use of material as possible the area of the main bearing bore had to be reinforced in order to counteract bearing deformation. In this way it was possible to retain existing bearing technology despite the higher load. Compared to the previous design status the crankshaft was reinforced in the web area and cylinder spacing was consequently increased by 3 mm.
kets due to entrained impurities. The cooling of the returning fuel is accomplished by a small plate heat exchanger that is integrated into the low-temperature circuit of the intercooler. Consequently, the hot fuel is cooled even in systems without a fitted raw water heat exchanger. There is no longer any need for a return line to the tank. Due to the free engine vee air ducting was designed in such a way that in interaction with the charging assembly a completely new arrangement was created that saves bulk volume and weight, Figure 3. The intercooler was positioned between the cylinder banks. The walls of the junction box exposed to hot air are created by the crankcase through which cooling ducts pass. In this way the surface temperature can be kept below 220°C. Via the upper, cold junction box and air ducts along the engine the charge air is fed to the cylinders.
The service block module from the current series was used. At the free end of the engine there are the charge cooler, the filter, and fuel ducts. One new feature is a cooling water filter in order to avoid wear on gas-
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be achieved with two-stage supercharging in the engine size discussed here. Against this background, the single-stage supercharging system used represents a low-cost type of charging with minimal bulk volume requirement. Important criteria in the development of a turbocharger are high levels of efficiency for implementation of a favorable gas cycle at the cylinders and a broad compression performance map, Figure 5, in order to satisfy the high torque demands of the diesel engine. Due to the optimized compressor blading total compression ratios up to 5 are achieved at a circumferential speed of 580 m/s. Optimal isentropic efficiency is 79%. The material used for the compressor turbine wheel is aluminum. On account of the low density it has a positive impact on the moment of mass inertia and hence on the acceleration response of the turbochargers. 3.2 Air and Exhaust Gas Ducts
3 Turbocharging Concept
In order to achieve the development targets with regard to the high power-per-cylinder ratio and the broad engine map the supercharging system of the 2000 CR engines was enhanced on the basis of the preceding model. The essential features are single-stage supercharging with newly developed MTU exhaust gas turbochargers; heat losses at the exhaust end are minimized due to complete air gap insulation of the exhaust gas lines, including the turbine scrolls, by means of a turbocharger support housing; the air-end pipe lengths were reduced by integration of the intercooler into the engine vee. The permissible surface temperatures are met by cooling the compressor scrolls and subjecting the intercooler matrix to flow via the upper deck of the crankcase. In order to provide sufficiently high supercharging pressure even at low engine speeds MTU's proven sequential supercharging is used. The supercharging system of the 12V and 16V engines is comprised of a main turbocharger and two sequential turbochargers, and on the 8V and 10V engines one main and one sequential turbocharger are used on each one. In order to fine-tune the turbocharger circuit two exhaust gas waste gates are used. 3.1 Exhaust Gas Turbochargers
2.2 Modular Design of Engine Components
Marine Engines
A key element for implementation of boosting power on series 2000 CR is the newly developed turbocharger series ZR125, Figure 4. It allows single-staged turbocharging at a supercharging pressure of 4.0 bar at the 1DS rated power point (fast ships with low load factors); a supercharging pressure level that can otherwise only
For uniform development of power on all cylinders it is necessary during the gas cycle to ensure identical thermodynamic states at the inlet valves of all the cylinders. On series 2000 CR it is accomplished by placing a common “tank” upstream of the cylinders. This function is handled by the air duct of the intercooler, which is at the center of the engine vee. The exhaust flow of the two cylinder banks is merged downstream of the turbochargers so there is only one exhaust outlet for all the cylinder variants. In order to control the high compression temperatures the charge air is fed to the intercooler matrix via the crankcase deck just downstream of the charger. Consequently, the hot charge air remains in the “interior” of the engine and no additional measures are required to maintain the permissible surface temperature. In order to reach the high charging pressures and the low levels of fuel consumption the energy losses at the exhaust end were considerably reduced again by comparison with the preceding model. This was achieved by providing the exhaust gas lines including the turbine scrolls, which were integrated into an exhaust gas turbocharger carrier housing, Figure 6, with complete air gap insulation. In conjunction with common rail injection, optimized-emission combustion harmonization and compound charging, series 2000 CR achieves an engine map breadth that even covers extreme marine applications, Figure 7. 4 Combustion System
The combustion system was newly developed for the 2000 CR. The focus was on cur-
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COVER STORY
Marine Engines
rent and future emission limits as well as low fuel consumption. An important objective was to fully exploit the advantages of the common rail system, which is being used in this series for the first time, at a maximum system pressure of 1800 bar. The given limits had to be met without exhaust gas recirculation and without exhaust aftertreatment but conventional combustion had to be used with optimized charging technology as well as a modern injection system. For each respective emission limit the Table shows an optimizedconsumption harmonization was selected and generally standardized hardware was employed. The combustion system was redesigned for series 2000 CR. It is vortex-free and uses a flat w-formed piston bowl and steeply arranged injection jets. Whereas on the existing engines in series 2000 the interaction between the edge of the piston bowl and the flatly positioned injection jet was utilized for mixture formation, on the new engine this is almost solely accomplished by the kinetic energy of the injection jet. This calls for a high-performance injection system like the common rail system, finetuned for this application. The emission values are maintained for all target applications, or levels are lower, and fuel consumption is also minimal. Combustion takes place relatively late. Here the flat w-formed piston dish with steeply arranged injection jets represents an additional advantage over the combustion chamber design used on series 2000 to date with re-entrant bowl and flatly arranged injection jets because the interaction of the flame with the liner is reduced, so very little carbon is entrained into the engine oil. Moreover, due to the flat dish the thermal load on the piston, and hence also contamination of the piston ring grooves, is reduced substantially. All in all, therefore, the result is a combustion system that satisfies not only combustion requirements but also thermal and mechanical demands for the combustion chamber. At a combustion ratio of ε = 15 a cylinder peak pressure of pmax = 180 (+10) bar is achieved. 5 Analytical Sizing of the Hydraulic System of Common Rail Injection
It is the aim of optimal combustion to minimize emissions like NOx, carbon, and white smoke and simultaneously to keep fuel consumption low throughout the entire performance map of the engine. For this reason the injection system has to meter the flow of injected fuel accurately, minimize the scatter by hydraulic interaction
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from cylinder to cylinder, and optimize the values for the start, duration and pressure of injection at each point on the performance map. 5.1 Modeling and Concept Comparison
The results of simulation are presented in Figure 8. Here an 8-cylinder vee-type engine was used as a basis. The left half of the picture shows the mathematical results of a common rail system with a pressure reservoir for each cylinder bank (conventional CR system). The top picture shows the pressure characteristic in the inlet of the injector at rated power at a system pressure of 1800 bar. The center picture shows the pressure characteristics in the blind hole of the injection needle according to the firing sequence of the engine within one working cycle. In addition, the pressure in the injection nozzle of cylinder B2 is shown. At the end of injection the maximum pressures occur at this point and in the present case the peak pressure is 2150 bar so it is 350 bar above system pressure, which represents a high load on the injection nozzle. In the bottom picture the pressure characteristics in the blind hole of the injection nozzle of all eight cylinders during injection were placed on top of one another. The visible differences were caused by hydraulic interaction from cylinder to cylinder. The right-hand half of the picture shows mathematical results of a common rail system with pressure reservoir integrated into the injector, whereby the top picture shows the pressure characteristic in the individual reservoir of the injector for cylinder B2. If reservoir volume and inlet pipe are matched appropriately, the peak pressure can be reduced sufficiently so that the level does not fall below system pressure at any time. The bottom picture shows, by analogy with the left-hand half of the picture, the pressure characteristics placed on top of one another during injection in the blind hole of the injection nozzle. In terms of quality, scatters are no longer visible because scatters due to hydraulic interaction are about 10 times less than on a conventional CR system, so from cylinder to cylinder a very uniform metering and atomization of the fuel is achieved. 5.2 Mode of Operation and Advantages of the CR-Ssystem with Individual Reservoir
In practice the common rail injection system with individual reservoirs in the injectors proves to be highly advantageous. The energy required for injection is provided by
the individual reservoir, exploiting the volume elasticity of the fuel. For this reason the inlet pipe can be relatively small so only the reservoir “discharged” downstream of injection is “charged” again until the next working cycle. During injection the inlet pipe acts like a hydraulic resistance so the undesirable hydraulic interaction from cylinder to cylinder is avoided. The function of the rail is reduced to supplying fuel. The reservoir is sized so that reservoir pressure drops up to the end of injection and peak pressure at the end of injection thus remains below a specified limit. 6 Design Configuration of the Common Rail Injection System
The common rail system in series 2000 CR was optimized hydraulically, Figure 9. A low-pressure pump flanged to the highpressure pump draws the fuel from the tank and takes it to the high-pressure pump via a filter fitted to the engine. The flow of fuel required for the injection process and for maintaining system pressure is provided via a pressure relief valve integrated into the high-pressure pump. This is determined by the electronic engine control with information on system pressure and engine speed and is actuated according to a stored performance map. A high-pressure line takes the fuel from the pump manifold volume to the distributor fitting, which accommodates an integrated high-pressure sensor, temperature sensor, and overpressure valve. From the distributor fitting there is a line to the distributor rail on each side of the engine. The distributor rail does not have a storage function but solely handles the function of a line. The hydraulic resistance upstream of each injector is provided by a restrictor bore at each high-pressure connection to the injector in the distributor rail. Consequently the line to the injector can be sized according to standard dimensions, which in turn is advantageous in terms of flexibility (possible tolerance compensation) and costs. Due to the off-center longitudinal bore in the distributor rail it was possible to integrate fixing threads and high-pressure connections into the distributor rail. As a result, the distributor rail was incorporated into the charge air pipe and hence it is of two-wall design. According to the hydraulic design, individual reservoir volumes were integrated in the injectors. Since with a conventional cylinder head cover the reservoir volume of the injector would come to rest in the oil chamber of the valve timing system, a solution was sought which would separate the reservoir
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from the oil chamber. This is achieved with two separate cylinder head covers, Figure 10. At the same time it was thus possible to shroud the high-pressure lines from the distributor rail to the injectors so this line itself can be of single-wall design. Contacting of the injectors was thus transferred from the oil chamber to the “dry” leak fuel chamber. The entire high-pressure system was of double-wall design due to the described configurations. Any leaks at highpressure seals cannot escape outward or into the oil chamber but are collected in the leak fuel chamber and detected centrally by a sensor. The injector is operated by a 2/2-way valve that is actuated by the electronic engine control. The control voltage is up to 42V. The control valve was placed as close as possible to the nozzle needle so that there are only slight delays between valve opening and nozzle needle opening. This design thus has the potential for multiple injection, without design changes having to be implemented on the control unit.
novative data storage and troubleshooting concept simplifies handling in the event of servicing and logistics. Updates are performed automatically via the system interface. The data storage concept makes it possible, in the event of the ECU7 having to be replaced, to copy the data from the engine management system, e.g. parameter set, engine operating hours, and other “lifetime” data of the engine, to a new ECU7 without an additional service tool being required. This functionality ensures that no relevant data gets lost. The parameters that define engine response are separate from system parameters. That means it is possible to handle the data independently. Once the engine has been tested it can be adapted to a wide variety of systems situations using various system parameterization without modification of the engine parameter set. ■
7 Electronic Control of the 2000 CR
One major innovation in series 2000 CR is the new generation of MTU's proprietary electronic engine management system. During development of the equipment the diesel engine was regarded as an integral part of the propulsion system from the very beginning. Special attention was paid to a more customer-friendly integration of the engine into the powertrain. For this purpose, in addition to the engine controller (ECU7) a system interface (SAM1) was developed which provides the customer with a whole host of capabilities and advantages. The controller was designed to be much more rugged than previous equipment so it is better adapted to the tough conditions at the engine. In the development of the engine management system the key features integrated into the SAM1 were a flexibly programmable system interface and flexible functionality. That means that the ECU7 contains much fewer customer-specific and system interface-specific settings. The variants for the different applications are implemented by the SAM1 using appropriate configuration data. Due to the use of a standard Compact-Flash card in the SAM1 programming the SAM1 system interface in the field is simple. An Ethernet interface opens up the opportunity for teleservicing for the engine management system on the Internet and due to a remote reading function for various engine and system data it allows optimized fleet management. An in-
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