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plication range of the power turbine comprises any mode where
excess exhaust gas from the turbocharging system is available.
This is especially the case when the two-stroke engine is charged
by highly efficient MAN turbochargers of the TCA series. Current
projects show that the turbines are suitable for both stationary
and marine applications. The modular arrangement of the power
turbine allows for the utilisation within full-scale waste heat recovery
solutions such as the MARC_HRS system of MAN Diesel
& Turbo, as mechanical drive for hydraulic pumps, as drive for
power take in to the crankshaft or as standalone units for power
generation in the form of turbo compound system with power
turbine and generator (TCS-PTG). With the enhanced automation
and control system, the stand-alone TCS-PTG on board the
vessel is capable of operating in island mode which makes it an
alternative to auxiliary gensets. With proven components from
MAN TCA and TCR turbochargers, it is possible to provide power
turbine solutions ranging from 500 kW up to 4 MW. The system
consists of the turbine itself, with axial and radial type turbines
capable of covering a wide flow range, gearbox, generator and
an advanced safety and automation that can be adapted to the
customers’ specifications. Integrated gear solutions result in a
compact and robust design. Matching the power turbine with
engine requirements results in a superior overall performance
of the complete system regarding the reduction of fuel oil consumption.
The arrangement of the valves together with the drives
as well as the advanced control system with redundant safety features
are considered as MAN Diesel & Turbo’s core competencies
that guarantee a smooth and reliable operation. The convincing
technical and commercial concept led to several customer orders.
In the course of order processing, the performance of all components
and systems has been scrutinised excessively via burner
rig and factory acceptance tests. The results are used to further
enhance the performance and reliability of the system. By consequently
following the building block principle, we exploit internal
and external synergies and make sure that our power turbine
creates real value added, reasonable amortisation periods and a
sustainable reduction of the emissions of modern diesel engines.
In the paper the design, automation and control philosophy is
presented in detail as well as the product portfolio and the test
results related to the current customer projects.
Solutions for better engine performance at low load
by Mitsubishi turbochargers
Yoshihisa Ono, Mitsubishi Heavy Industries, Ltd, Japan
Due to recent increases in fuel prices, many shipowners are seeking
reductions in operating costs, with particular emphasis on
lowering fuel consumption. Furthermore, for the sake of environmental
preservation, international societies have been moving
to tighten regulations on marine emissions of greenhouse gases
and NOx, with Tier II NOx regulations for ships having been
implemented in 2011 and Tier III regulations coming into force
in 2016. Also, a CO 2
emissions index (EEDI) will be applied to
vessels built from 2013 onwards, and CO 2
emissions regulations
based on this index will be become mandatory. Given that turbochargers
used for diesel engines have a substantial influence on
the combustion of fuel, they can play a major role in addressing
the above-mentioned issues. Of particular note in this context is
the fact that low load operation has come to be utilised in recent
years in order to reduce fuel consumption by ships. The author of
the present report, being associated with a turbocharger manufacturer,
is of the opinion that the application of several new turbocharger
technologies will be contributed to improved performance
by ships under low load operating conditions, in the form of
turbochargers specifically intended for these requirements. This
paper introduces technological efforts aimed at improved turbocharger
performance under low load conditions, incorporated
into the newest MET-MB series of high efficiency turbochargers
by Mitsubishi Heavy Industries (MHI). Also presented, MHI has
developed a new type of variable nozzle structure. The proprietary
MHI approach, known as the variable turbine inlet (VTI), has
been introduced not only for newly manufactured turbochargers,
but also as a retrofit option for turbochargers in current service.
The MET-VTI turbocharger is aimed at reduced fuel consumption
at low load for marine diesel engines. In order to actively increase
the amount of air in the low load operation, this MET-VTI was
increased turbine output by means of reducing the geometry turbine
area, thus enabling higher turbocharger rpm. In addition,
in the wake of the world’s first practical application in 2011 of a
turbocharger equipped with a high-speed generator (hybrid turbocharger),
discussion is presented on the current state of efforts
related to new hybrid turbochargers equipped with motor on the
rotor shaft, enabling motoring assist aimed at meeting low-load
operation requirements.
Computational investigation of turbocharger
performance degradation effect on two-stroke
marine diesel engine performance
Nikolaos Sakellaridis, National Technical University of Athens, Greece
Dimitrios Hountalas, National Technical University of Athens, Greece
Turbocharger condition is critical for the performance of turbocharged
diesel engines and especially large scale two-stroke ones.
In this case, in addition to increasing power density, the turbocharger
must also maintain a positive difference between exhaust
and inlet pressure to facilitate cylinder scavenging. In large scale
two-stroke diesel engines the mass flow through the engine, and
therefore A/F ratio, is greatly influenced by turbocharger performance.
In the present paper a theoretical investigation to determine
and quantify the effect of turbocharger performance degradation
on the performance characteristics of a slow speed two-stroke
marine diesel engine is presented. The closed cycle is modelled
using a multi-zone phenomenological combustion model. For
the gas exchange, the filling and emptying method is applied.
The model has been extensively validated for cases of heavy duty
four-stroke diesel engines, and has been modified to capture special
characteristics of large two-stroke diesel engines operating on
HFO. The T/C turbine and compressor are simulated using newly
developed physically based quasi-dimensional models. Flow is
solved at key stations along the T/C components , while flow
losses and angles are derived from semi-empirical correlations.
For the turbine a modified version of the Ainley and Mathieson
axial turbine performance prediction technique is applied. The
compressor is modelled using a meanline model of radial compressor
performance. For the turbomachinery models calibration,
data from the engine’s NOx technical file are used (where
air and exhaust gas flow data are provided). Thus, the problem of
limited availability of turbomachinery maps is resolved, which is
very common for field applications. The complete engine model
is validated through the comparison of predicted performance
data with the corresponding values of the shop tests. Using the
model, various scenarios of turbocharger performance degradation
are investigated. The effect of turbine efficiency reduction,
compressor efficiency reduction saw as their simultaneous reduction
are investigated with respect to their impact on engine
performance. The effect of turbine nozzle ring fouling on engine
operation is also investigated since this is a common problem for
two-stroke marine diesel engines. From the analysis of generated
results it is possible to develop a methodology for turbocharger
condition monitoring that will allow safe detection of the actual
component fault.
May 2013 | Schiff&Hafen | Ship&Offshore SPECIAL 37