Document number 202044
Date of issue 6 May 2016
Product RT-flex50 conversion to DF generic manual
Version a1
DF
Re
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Inst
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WARTSILA RT-FLEX50 DUAL FUEL RETROFIT GENERIC MANUALG
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© Copyright by Winterthur Gas & Diesel Ltd.
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Preface
The Wartsila RT-FLEX50 DUAL FUEL RETROFIT GENERIC MANUAL is intended as an initial
guide when planning to retrofit a conventional diesel / HFO burning Wartsila RT-flex50
installation for future operation on natural gas. Since each existing installation is unique, this
document shall be seen as a generic check list with main focus on modification work required
on the main engine.
Every retrofit project requires a thorough vessel specific investigation, analyzing the impact and
modification need on: the engine, the engine room ancillary systems, control and alarm systems
and the hazardous zones around gas related equipment and venting pipes.
In parallel to this dual fuel retrofit check list focusing on modifications on the main engine, it is
highly recommended to study the “RT-flex50DF Marine Installation Manual”, to get a better
understanding of the requirements for gas related auxiliary equipment to be installed in the
engine room or on deck.
Winterthur Gas & Diesel Ltd.
Product Information
Schützenstrasse 1-3
PO Box 414
CH-8401 Winterthur
Switzerland
Tel: +41 52 262 07 14
Fax: +41 52 262 07 18
www.wingd.com
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Table of contents
1 RT-flex50DF engine output parameters ................................................................................................ 6
1.1 Maximum nominal output difference between conventional flex50-D main engine and
flex50DF main engine. .............................................................................................................................. 6
2 Engine outline comparison ................................................................................................................... 8
2.1 Outline view example of RT-flex50DF engine with turbo charger at aft end ............................... 8
3 DF conversion – influence on built on engine components ................................................................. 9
3.1 Component group categories for RT-flex50-D and RT-flex50-DF engines .................................... 9
3.1.1 Engine component groups common / components remaining unchanged ......................... 9
3.1.2 Engine components groups to be replaced when converting to DF ................................... 11
3.1.3 Engine component groups to be evaluated for each conversion project, the component
groups may need total replacement or partial equipment modification ........................................... 12
3.1.4 New engine component groups to be built on the engine when converting to DF ........... 13
3.1.5 Engine control system ......................................................................................................... 15
3.1.6 DF engine specific tools....................................................................................................... 16
4 DF conversion – essential new components off engine ..................................................................... 17
4.1 New engine room equipment to be taken into consideration when converting to DF ............. 17
4.1.1 Shaft power meter .............................................................................................................. 17
4.1.2 Gas valve unit (GVU) ........................................................................................................... 17
4.1.3 Pilot fuel system .................................................................................................................. 18
5 Engine room systems and equipment ................................................................................................ 19
5.1 Engine room systems and topics requiring attention when converting to DF ........................... 19
5.1.1 Class rules valid at the time of conversion ......................................................................... 19
5.1.2 Safety – gas detection – gas release ................................................................................... 19
5.1.3 HT cooling water expansion tank ........................................................................................ 19
5.1.4 Exhaust gas system ............................................................................................................. 19
6 LNG tank and gas feed system ............................................................................................................ 20
6.1 LNG tanks and gas processing ..................................................................................................... 20
7 Conclusion ........................................................................................................................................... 21
7.1 Conversion of existing Wärtsilä 2-stroke flex installations ......................................................... 21
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1 RT-flex50DF engine output parameters
1.1 Maximum nominal output difference between conventional flex50-D main
engine and flex50DF main engine.
Wartsila 2-stroke DF engines have a lower maximum continuous rating (MCR) compared to similar bore
size liquid fuel burning engines. Since DF technology is based on the Otto combustion principle there are
cylinder pressure MEP limitations persisting, that to avoid knocking / pre-ignition in the combustion
chamber, consequently the maximum available engine output is reduced.
For every conversion project, the vessel’s original propeller characteristics have to be carefully
evaluated and compared to the available engine power after converting to DF. Depending on the
original propeller layout and the originally selected CMCR, diesel burning RT-flex50 installations
converted to gas burning RT-flex50DF installations, may have to accept lower sailing speeds. In certain
cases it may also be necessary to exchange / modify the propeller.
Table 1, Maximum output difference between RT-flex50D and RT-flex50DF
RT-flex50-D RT-flex50DF
Power/cyl. R1 (kW) 1745 1440
Power/cyl. R4 1020 955
Speed R1 (rpm) 124 124
Speed R3/R4 (rpm) 95 99
Bore (mm) 50 50
Stroke (mm) 2050 2050
MEP Introduction (bar) 21.0 17.3
Cyl. config. 5-8 5-8
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The operating field after converting to DF need to be within the operating points outlined with green
lines.
Figure 1, Visual graph of common operating field
Conclusion: It may be necessary to change the propeller when converting to DF.
77%
58%
77%
55%
66%
83%
80%
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2 Engine outline comparison
2.1 Outline view example of RT-flex50DF engine with turbo charger at aft end
The physical installation space requirement is the same for both engine types, except for the upper
platform, which is somewhat lengthened at the free end side for RT-flex50DF engines. The pilot fuel
pump unit is located on the upper platform free end side, making the platform longer, nevertheless, for
conversion projects the pilot fuel pump unit can be relocated and installed on the hull side. Therefore
we consider the space requirements identical regardless of RT-flex50-D or RT-flex50DF.
Below engine illustrations of a 5RT-flex50DF focuses on gas specific components and rerouted piping
installed on the engine.
FUEL SIDE OUTLINE VIEW EXHAUST SIDE OUTLINE VIEW
Figure 2, Fuel side outline view respectively exhaust side outline view
Conclusion: The physical engine space requirements do not change after gas related equipment is
installed.
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3 DF conversion – influence on built on engine components
3.1 Component group categories for RT-flex50-D and RT-flex50-DF engines
Engine components have been categorized into 6 categories. Category 1 indicates components, which all
remain unchanged. Category 2 indicates components that have to be replaced when converting to DF.
Category 3 lists components that will require project specific consideration. Category 3 parts might be
suitable for use in some projects, but might as well need replacement. Category 4 lists DF components
which are not installed on conventional liquid burning engines and are new components to be added on
the engine when converting to DF. Category 5 concerns automation and is applicable to both
automation on the engine, as well as to the remote control and alarm system in the engine control
room. Category 6 focus on items, which as such are not relevant for the DF retrofit, but are important in
order to ensure the possibility to carry out proper maintenance later on.
3.1.1 Engine component groups common / components remaining unchanged
- Bedplate with main bearings
- Thrust bearing
- Engine column
- Drive supply unit
- Column doors
- Air water separator
- Turning gear
- Piston cooling
- Gland box
- Crankshaft
- Connecting rod
- Exhaust gas valve arrangement
- Supply unit arrangement
o Common rail fuel pump
o Fuel pump casing
o Gear wheel
- Servo oil pump
- Auxiliary blowers
Illustration of parts being identical
Figure 3, bedplate Figure 3, gear wheel Figure 5, thrust bearings
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Figure 6, crank shaft Figure 7, gland box Figure 8, turning gear
Figure 9, connecting rod Figure 50, supply unit Figure 41, free end cover Figure 12, crank case explosion relief valves
Figure 6, A-frame
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3.1.2 Engine components groups to be replaced when converting to DF
- Cylinder units
o Cylinder covers
o Pistons
o Piston rod
o Cylinder liner / liner insulation tube
o Cylinder jacket
o Water guide jacket
- Cylinder lubrication
- Fuel injection / exhaust gas drive / servo oil regulation linkage arrangement modification
- Tie rods
- Rail unit
- Fuel rail
- Servo oil rail
- Exhaust gas valve control unit
- Scavenge air receiver explosion relief valve
- Cross head guide shoe
- Bearing shell cross head
- Crank pin bearing shell
Illustrations of parts that need to be exchanged
Figure 75, rail box Figure 94, piston rod, piston Figure 86, cylinder liner
Figure 17, cross head pin and guide shoe
Figure 118, cross head upper bearing cap
Figure 10, air receiver Figure 20, water guide jacket
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3.1.3 Engine component groups to be evaluated for each conversion project, the
component groups may need total replacement or partial equipment modification
- Turbo charger
- Exhaust gas manifold
- Scavenge air receiver
- Scavenge air cooler
- Air piping
- High pressure fuel piping
- Water piping
- Oil piping
- Measuring and instrumentation detection
- Cylinder block (requires machining or replacement)
- Starting air valve
- Cross head bearing lubrication pump (mandatory for DF engines, project specific for
conventional liquid burning engines)
- Control box for local maneuvering
Illustrations of parts that may need replacement or modifications
Figure 22, turbo charger Figure 23, scavenge air cooler
Figure 24, control panel for local maneuvering
Figure 212, exhaust gas manifold
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3.1.4 New engine component groups to be built on the engine when converting to DF
- Gas admission valves
- Gas supply pipe manifold
- Pilot fuel oil supply injectors
- Pilot fuel oil supply pump and piping
- Exhaust gas waste gate
- Piston underside gas detection system
Figure 25, essential new components. Pilot fuel pump (blue), pilot fuel pipes (blue) and gas pipe manifold (yellow).
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Figure 26, gas admission valves with hydraulic pipes
Figure 27, gas pipe manifold mounted on engine
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3.1.5 Engine control system
RT-flex50DF control is based on “UNIC” meanwhile conventional RT-flex50D are based on “flex” control
technology.
When converting a conventional RT-flex50-D engine to RT-flex50DF all electrical and automation
systems and their components need to be updated for UNIC compatibility.
Sensors and automation components applied on engines to be converted need to be checked for UNIC
compatibility.
Remote control and alarm and monitoring systems (off engine) need to be replaced or updated for UNIC
compatibility.
Figure 27, UNIC based
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3.1.6 DF engine specific tools
The majority of engine related tools delivered for an RT-flex50-D engine can be used after converting to
DF. Only a small number of tools need to be replaced or modified.
Short list of important tools to be replaced or modified:
- Piston assembly lifting tool
- Piston measuring tool
- Piston ring assembly tool
- Fuel injector test bench (adaptation)
- Cylinder liner insulation tool
- Tie rod pre-tensioning tool
- Injection valve grinding tool
- Software download package tool
- Tool emergency cylinder lubrication
- Tool for gas admission valve (new)
Other tools may be concerned but need to be evaluated on a project by project basis.
Short list of tools requiring project specific investigation:
- Scavenge air cooler lifting tool
- Turbo charger tools
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4 DF conversion – essential new components off engine
4.1 New engine room equipment to be taken into consideration when converting
to DF
This document focuses mainly on modifications on the engine, but some few pieces of equipment
being essential for functionality will be mentioned.
4.1.1 Shaft power meter
On conventional Wärtsilä 2-stroke flex engines a number of engine operating parameters are
used for calculating a fairly accurate power output estimate. The estimated power output is
sufficient feedback for injection control of correct liquid fuel amount.
Duel fuel engines operating in gas mode require a more accurate engine load feedback signal.
Therefore a shaft power meter has to be installed to provide the engine’s actual load feedback
signal.
Shaft power meters are not mandatory on board conventional liquid fuel burning vessels and
may or may not be installed. In case a shaft power meter is already installed, it can most likely
provide the necessary engine load feedback signal required for DF engines operating in gas
mode.
Figure 28, example of shaft power meter
4.1.2 Gas valve unit (GVU)
The required gas pressure before the gas admission valves varies with the engine load. To
accurately control the gas pressure before the gas admission valves, a gas pressure regulating
valve is required. Wärtsilä offers suitable gas valve units of open or enclosed type. When
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selecting an enclosed type gas valve unit it becomes a part of the double wall gas piping and can
be installed inside the engine room, meanwhile an open type gas regulating unit must be
installed in a dedicated gas valve room.
Figure 29, GVU
4.1.3 Pilot fuel system
MDO fuel feed pumps, filters and equipment for pilot fuel feed system have to be added to the
engine room ancillary equipment.
Figure 30, GVU-EDTM
Figure 31, Pilot fuel system
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5 Engine room systems and equipment
5.1 Engine room systems and topics requiring attention when converting to DF
This document focuses mainly on conversion modifications on the engine, but some few pieces of
engine room equipment being essential for functionality and safety will be mentioned.
For more detailed information reference is made to the Marine Installation Manual (MIM).
5.1.1 Class rules valid at the time of conversion
Compliancy to class rules has to be assured. Every vessel conversion has to be engineered in
close cooperation with the class.
5.1.2 Safety – gas detection – gas release
Attention has to be paid to safety. With double wall gas piping the engine room is considered a
gas safe machinery space, single failure will not lead to gas release into the machinery space. To
monitor that no gas leakage occurs, gas sensors have to be installed in the engine room. The
number and position of the gas sensors have to be confirmed by the class.
The annular space between the double wall pipes has to be continuously ventilated, as per class
requirements.
Any potential intended or unintended release of gas has to be diverted to a hazardous zone
outside the engine room. Released ignitable gas will dilute quickly to a concentration level
below the lower explosion level (LEL).
Auxilliary systems shall be designed with focus on mitigating the impact of a potential
malfunction.
5.1.3 HT cooling water expansion tank
Separated cooling water low temperature and high temperature expansion tanks are
recommended for DF installation. During an abnormal engine operation (crack in cylinder liner,
exhaust gas valve cage or pilot fuel pre-chamber) it may be possible that the HT water circuit
gets contaminated with gas, ending up in the high temperature cooling water expansion tank.
The HT cooling water expansion tank has to be of closed type and classification societies might
require a gas detector to be installed in the expansion tank, as well as extending the venting
pipe to appropriate place.
5.1.4 Exhaust gas system
The exhaust gas pipe shall be designed in such way that gas cannot accumulate in the exhaust
system. Measures have to be taken to prevent damages in case gas would accidently enter the
exhaust gas piping and cause an explosion in the exhaust gas pipe. There are two possible safety
measures to mitigate the impact of an explosion in the exhaust gas piping, both alternatives are
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based on pressure release in case of an explosion. Over pressure safety devices to be installed in
the exhaust gas piping can be rupture discs (requiring separate exhaust ducts releasing exhaust
gasses outside the hull after rupture), or spring loaded exhaust gas relief valves. The number
and position of pressure relief devices are installation dependent.
6 LNG tank and gas feed system
6.1 LNG tanks and gas processing
This document focuses mainly on conversion modifications on the engine. Each conversion
project requires a detailed study focusing on the LNG tanks and gas processing equipment.
Factors to consider when determining the LNG tank design and size are:
- Vessel operating profile, days of autonomy between each LNG tank fill up
- Positioning of LNG tanks on the existing vessel?
- Where can compressors and re-gasification equipment be installed?
Wärtsilä offers LNGPacTM solutions with the following benefits:
- Type C pressure vessel. Design pressure 6-9 bar.
- Pressurised or cryogenic pump based gas feed solution.
- Vacuum (MLI and Perlite) or polyurethane insulation.
- Horizontal, vertical, longitudinal and transversal placing.
- LNG process equipment located inside built-on tank connection space or deck mounted
vaporising skid.
- Class approved safety and control system.
- Remote actuated and manually operated cryogenic valves.
- Dedicated control and monitoring system.
Figure 32, LNGPacTM
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7 Conclusion
7.1 Conversion of existing Wärtsilä 2-stroke flex installations
Conversion of existing liquid fuel Wärtsilä 2-stroke installations is possible, thereby enabling the ship
owners to enjoy the benefits operating on gas as fuel. When operating in gas mode the emission
benefits are:
Low NOx emissions, Tier III compliancy without exhaust gas after treatment
Particulate matter emissions reduced to close to zero
No SOx emissions