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Service Bulletin RTA-79.2RT-flex-08.211.03.2009

Technical Information to all Owners / Operatorsof Wärtsilä RTA and RT-flex Engines

Continuous Low Load Operation(Slow Steaming)

Contents1 Introduction 12 Considerations 13 Recommendations 14 Related Documentation 2Improve Engine performance and runningbehaviour 3

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1 IntroductionWärtsilä 2-stroke engines are optimised for operation in the load rangeabove approximately 60% CMCR. Continuous running at lower loads downto 10% CMCR is possible, but with special care.

This document is intended to give additional recommendations on whatneeds to be observed when operating the engine continuously at loads lowerthan the above mentioned 60% engine load, and it introduces also the “SlowSteaming” upgrading solution.

These recommendations are given, assuming that no components arechanged nor engine tuning is modified, in order to remain within thelimitations imposed by IMO emission regulations. Any further measuresrequire recertification of the engine with new or amended Technical File.

2 ConsiderationsAt lower engine load between approximately 60% and the auxiliary blowerswitch-on/off point, the turbocharger efficiency is relatively low.Within this power range the engine operates with a lower air/fuel ratioresulting in higher exhaust gas temperatures.

The RT-flex engines are more advantageous for continuous operation onload down to 10% CMCR than the RTA models, due to their uniqueelectronically controlled common rail injection system. They allow forhigher injection pressure and selective fuel injector cut-off at very lowloads, thus reducing excessive carbon deposits, exhaust gas economiser andturbocharger fouling.

3 RecommendationsThe following recommendations should be observed, in order to limit theadverse effects of continuous low-load operation as much as possible:

The basic prerequisite needs to be in order:

The fuel valves should be well operating & maintained. Any possiblesign of shorter TBO to be observed.

Fuel injection viscosity should be maintained at the lower end of therecommended 12 to 17 cSt as specified in the engine operating manual,anyhow without exceeding 155°C at engine inlet.

Keep the LT cooling water temperature at 36°C in order to maintain theoptimum scavenge air temperature and the jacket cooling watertemperature at the upper limit (85 - 95°C).

The turbocharger(s) should be cleaned and maker’s recommendationsfor soft cleaning to be followed

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The cylinder oil feed rate is load-dependent and, if correctly tuned (seerelated chapter of operation manual or service bulletins), re-adjustment isnormally not required. However, frequent piston underside inspections arerecommended to monitor piston running conditions and signs of over-lubrication.

The exhaust gas temperature after the cylinders should be kept above 250°Cin order to reduce cold corrosion, fouling of exhaust gas receiver andturbocharger nozzle ring. If the exhaust gas temperature drops below thisvalue, the engine load should be increased.

If the exhaust gas temperature gets too high (>450°C after cylinders), theauxiliary blower may be switched to “continuous running”. However, it hasto be taken into account that not all auxiliary blowers and circuit breakersmay be suitable for continuous running at electrical loads above nominalcurrent.

Repeatedly switching-on and -off of the auxiliary blower must be avoided. Ifnecessary, the auxiliary blower controls have to be switched to “manualoperation”, or operation in this load area has to be avoided.

Note also to inspect and if necessary lubricate the bearings more frequentlyif seen needed due to increased operation of the blower. This also includesthe inspections of the non-return valves for the scavenging air.

A concern during continuous low load operation is the accumulation ofunburned fuel and lubricating oil in the exhaust manifold, as such depositscan ignite after the engine load is increased again. This may result in severedamage to the turbocharger due to sudden over-speeding. Therefore, itshould be considered to periodically (twice a week) increasing the engineload as high as possible, however at least 70% for at least 1 hour, in order toburn off accumulated carbon deposits. The load-up has to be done verycarefully (i.e. during 2 hours) in order to avoid adverse piston runningconditions due to carbon that has built up on the crown land, and to avoidpossible exhaust manifold fire.

Also other related components (scavenging air receiver, exhaust gas valves,T/C grid, etc) need more frequent inspections and possible cleaning.

An economiser with closely-spaced fins may also require more frequent sootblowing.

4 Related DocumentationFor recommendations regarding low-load operation of Sulzer RN, RN, Mand RL engines, please refer to Service Bulletin RN-7.1 issued 08.02.1993.

For recommendations on cylinder lubricating oil settings, please refer toService Bulletins RTA-63 and RTA-76 / RT-flex-03.

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Improve Engine performance and running behaviour

Upgrade Kit “Slow Steaming”In order to further optimize the engine operation at low load, Wärtsilä has developed anupgrade kit “Slow Steaming”. The main technique behind performance optimization withthis patented solution is a variation in the number of operational turbochargers at differentloads.In practice this means that one (1) turbocharger is disconnected by means of closing a“blocking valve”, whereby the efficiency of the remaining turbocharger(s) will increase atlow engine load.

The Upgrade Kit “Slow Steaming” enables:

Operating the engine at lower load without operation of the auxiliary blower

Reduction the risk of turbocharger and economiser fouling

Significant reduction of specific fuel consumption

Additional fuel cost savings, on top of the savings due to low-load operation

Retrofit Pulse Lubrication SystemIn combination with the above described upgrade kit “Slow Steaming”, Wärtsilärecommends the installation of electronically controlled cylinder lubrication.

The Retrofit Pulse Lubrication System provides:

Optimal lubrication due to the precisely timed feeding of oil into the piston ring pack

Savings in lubricating oilThis well-proven concept can be installed on all Wärtsilä two-stroke engines

In order to get a specific evaluation of how the upgrade kit “Slow Steaming” (UGKSS) andthe Retrofit Pulse Lubrication System (RPLS) can be installed on your ship or fleet, kindlyask your usual local Wärtsilä network contact.

Likewise, estimated calculations for fuel and cylinder lube oil savings can be provided, inorder to determine investment pay-back times.