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with large-volume stationary gas engines used for power generation.
Here, an attempt has been made to assess the tribological
system comprising of piston ring and cylinder liner, which bears
the highest loss in a combustion engine in terms of energy. The
aim is to optimise mechanical, thermal and tribological load
bearing capacity of the system. The study also focuses on reducing
the probability of spontaneous failure of this system to result
in a greater reliability. This in turn would ensure continuous
power generation and safeguard the costs and resources. While
modern engine test benches are more than capable of testing the
aforementioned system of interest here, they are time consuming
and highly cost intensive. Also, post-test damage analysis in such
bench tests does not offer much of an insight into the occurrances
during the test. Therefore, a model scale, damage-equivalent test
methodology, was designed for a comprehensive assessment of
the system in a quite economical and time efficient manner. The
tests were carried out on a TE 77 test rig from Phoenix Tribology
with an analogous ’ring-on-liner’ configuration. The specimens
were cut out from real components. To verify conformity between
the two specimens, a light-gap-method was applied. The component
based test configuration facilitates damage-equivalent
investigation of the piston ring - cylinder liner system. Post-test
characterisation was also carried out to elucidate and substantiate
the findings from the tribological tests. The results obtained for
a generic tribosystem consisting of a low alloyed and tempered
spheroidal cast iron piston ring with a chrome ceramic layer, and
an untreated lamellar cast iron (EN-GJL-250) cylinder liner, were
considered as a reference. Numerous base materials with varying
surface treatments have been investigated through a series of
experiments to find an optimised solution that would offer an
increased tribological loading capacity, with improved efficiency
and reliability. The corresponding results facilitated in identifying
an optimised system w.r.t base material, thermal treatment,
topography, and lubricant. Finally, the results will be validated on
a test engine in order to verify whether the chosen system would
be suitable for a real life engine.
Tuesday May 14th / 08:30 – 10:00
Product Development
Diesel Engines – Two-Stroke Low-Speed Engines
Room A
Upgrade of Wärtsilä’s two-stroke engine portfolio to
fulfil the changing marine market requirement
Heinrich Brunner, Wärtsilä Switzerland Ltd, Switzerland
Jean-Noel Constantin, Wärtsilä Switzerland Ltd, Switzerland
Beat Schumacher, Wärtsilä Switzerland Ltd, Switzerland
Dominik Schneiter, Wärtsilä Switzerland Ltd, Switzerland
Wärtsilä’s current two-stroke portfolio consists of engine-types:
RT96C, RT84T-D, RT82C, RT82T, W-X82, RT68-D, RT58T-E,
RT60C-B, RT50- D and RT48T-D as well as the newly developed
WX35, W-X40, W-X62, W-X72 and W-X92 engines. The
RT-flex82T engine has been upgraded for modern requirements
and is presented in the portfolio as the new Wärtsilä W-X82 engine
for VLCC/VLOC (Very large crude/ore carriers) and Panamax
container vessels. Introduction of the new engine types W-X35 to
W-X92 will be described in a separate paper. By the end of 2012,
more than 1,000 electronically controlled Wärtsilä two-stroke engines
had been ordered. As these flex engines now account for
100% of the orders placed and RTA engines are no longer popular,
this confirms that the common rail technology is highly attractive
and well established. The trend of reduced ship’s service speeds
in combination with lower shaft speeds and lower engine powers
for engine newbuildings requires a continuous upgrading of the
existing engines in the portfolio. To cope with this trend, engines
are configured at lower ratings to gain the lowest possible specific
fuel consumptions and to achieve low EEDI (Energy Efficiency
Design Index) numbers. Therefore, e.g., the rating field of the
W-X82 engine was enlarged and the power of the RT-flex58T-E
engine has been increased by 4% in order to fulfil specific market
requirements. Additionally, an ’RT-flex’ version of the RTA48T-
D engine has been designed and released to meet the requests
mainly of the Chinese market. Also, on the RT-flex50, an engine
arrangement with the turbocharger at the aft end of the engine
has been introduced. This paper also reports on the development
of Wärtsilä’s RT-flex engines focusing on design improvements to
increase their reliability and serviceability, and to reduce maintenance
costs. Pulse Jet cylinder lubrication and FAST (fuel actuated
sacless technology) fuel valves have been introduced to gain
lower cylinder oil feed rates, lower fuel oil consumptions and reduced
emissions respectively. The first measurements with FAST
fuel valves during shop tests on different bore sizes confirmed
the potential of reduced fuel oil consumption over the whole engine
load range. The first engine with this new technology entered
service at the beginning of 2012. The above-mentioned major
improvements will be introduced on all portfolio engine types
step by step. Wärtsilä’s two-stroke engines can be equipped with
the intelligent combustion control (ICC) system, which adjusts
the peak firing pressure of the engine according to the given design
criteria and automatically balances compression and firing
pressures in all cylinders by selecting the injection timing and exhaust
valve closing within the allowed operating range. The waste
heat recovery (WHR) system, which has been installed on many
projects, will also be described in the paper and the operational
benefits will be reported. The second part of the paper will highlight
the wide range of service experience gained with the different
engines. From this service experience, the good engine performance
and reliability as well as the attractiveness of the common
rail engines can be confirmed. The first RT82C and RT82T engines
have exceeded four and three years of successful operation, respectively.
The total accumulated running time of 100 engines at
sea has reached more than 1,000,000 hours. Further, the first RTflex48T-D
engine passed its shoptest and was commissioned in
May 2012. A thorough insight into the behaviour of RTA and RTflex
components will be given, including information on fuel and
servo oil pumps, as well as injection control units and a review
of piston-running results. Additionally, the excellent performance
of crank train bearings will be mentioned. Broader service experience
of FAST injectors will be available after the validation test
at the beginning of 2013 and will be reported during the CIMAC
Congress. Releasing this promising technology is an important
milestone to reduce the greenhouse effect of low-speed marine
engines.
State-of-the-art MAN B&W two-stroke super-longstroke
engines
Susanne Kindt, MAN Diesel & Turbo SE, Denmark
Since the economical crisis was recognised worldwide in the autumn
of 2008, owners have been looking into cost savings, such
as slow steaming and optimised low-load operation with turbocharger
cut-out, exhaust gas bypass, etc. This has led to research
into optimised propulsion efficiency, available propeller sizes and
possibilities regarding stroke size for crankshafts. The result is now
known as the G engine series, including the G/40/45/50ME-B9.3,
G60/70/80ME-C9.2, S30ME-B9.3 and S90ME-C9.2. With the G
engine series, a new generation of super-long-stroke engines has
been introduced to the market and, in many cases, a new design
of the aft ship is needed to fully utilise the low revolutions of these
engines. However, the interest in the new engines is very high, and
May 2013 | Schiff&Hafen | Ship&Offshore SPECIAL 17