propulsion systems small vessels

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WÄRTSILÄ TECHNICAL JOURNAL 01.2010

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Fig. 1 – A 6-cylinder Wärtsilä RT-flex35 with simple platform arrangement.

Fig. 2 – The Wärtsilä RT-flex35 rail unit.

The most efcient propulsionsystems or small vesselsAU T HO R S: D a n i e l S c h m i d , P r o d u c t M a n a g e r , W ä r t s i l ä i n S w i t z e r l a n d, H e i n r i c h S c h m i d , G e n e r a l M a n a g e r , M a r k e t i n g &

A p p l i c a t i o n D e v e l o p m e n t , W ä r t s i l ä i n S w i t z e r l a n d a n d M a r c S p a h n i , P r o j e c t M a n a g e r , W ä r t s i l ä i n S w i t z e r l a n d

Two new, small-bore low-speed diesel

engines, the Wärtsilä RT-flex35 and

RT-flex40, are being developed to

extend Wärtsilä’s two-stroke engine

portfolio towards lower power

outputs.

Covering a power range o 3475–9,080 kW,the new Wärtsilä R-ex35 and R-ex40engines are intended or small andmedium-sized commercial vessels, such ashandysize bulk carriers, handymax bulk carriers and product tankers, break-bulk general cargo vessels, reeers, eedercontainer ships (say 500–1000 EU), and

small LPG carriers. In Europe and the Americas, such vessels are usually poweredby our-stroke engines with a geared drive.However, there is a very large market inEast Asia or small, crosshead-type low-speed engines, such as these new Wärtsiläengine types, or direct propeller drives. InEast Asia, such vessels are oten used orriver and coastal trade.

Te key benets o the new engines willbe their compliance with IMO ier IIexhaust emissions regulations, low uelconsumption, low cylinder oil eed rate,

high reliability, and long intervals betweenoverhauls. Tey will also be able to provideoptimum ts to the targeted ship types interms o power, propeller speed, dimensions, weight, and electrical power consumption,as well as being competitive inmanuacturing costs.

Te engines’ development is beingsupported by two partners; MitsubishiHeavy Industries Ltd (MHI) and YichangMarine Diesel Engine Co. (YMD).Mitsubishi is co-operating closely on theengine designs, contributing in particular

with its experience with small-bore, low-speed engines. From the Wärtsilä R-exengines, Mitsubishi is developing themechanically-controlled UEC engines. YMD will build the rst Wärtsilä R-ex35



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engines, and is co-operating in theengine design work with respect to their

manuacture and assembly. Te aim isto provide optimum engine value ormoney. YMD will also market the enginesin the important Chinese market area.

Layout flexibility As with all Wärtsilä low-speed engines,the R-flex35 and R-ex40 have greatexibility in the selection o engine powerand speed. Tis enables them to obtainthe optimum t to ship and propellerrequirements, thus rendering the mosteconomical installation. Te wide range o

power and speed covered by each engineis dened by a layout eld marked by thepower/speed rating points R1, R2, R3and R4, o which R1 is the maximumcontinuous rating (MCR). Any power andspeed within this engine layout eld may be selected as the Contract-MCR (CMCR)point or the engine.

The common-rail systemTese crosshead-type engines with uniow scavenging, are designed rom the outset with Wärtsilä R-ex common-rail

systems or ull electronic control o theuel injection, exhaust valve actuation,starting, and cylinder lubrication. Tistechnology will enable the engines tocomply with the new IMO ier II emissionsregulations while, at the same time,maintaining low uel consumption o 176 and 175 g/kWh at 100% load or theR-ex35 and R-ex40 respectively.

Te R-flex system is particularly suitedto the engines’ compact proles, beingoptimal in efciency, unctionality, lietime,size, weight, and service riendliness.

Concepts rom the well-proven common-

rail systems o Wärtsilä’s our-stroke engineshave been adapted to the R-ex35 and

R-ex40 engines. For example, inthe new engines, the injection control unitunctionality has been integrated into theinjector. Tereore it operates with time-controlled injection.

Tere are two solenoid-actuatedinjectors in each cylinder or optimizedinjection control at all engine loads.Te system includes mechanical ow limiters or each injecting unit.

Fuel oil and the servo oil or the engine’shydraulic system are delivered at regulatedpressures to common-rail pipes arranged

in a rail unit along the cylinder banks.Te servo oil is employed or actuatingthe exhaust valves with separate controlthrough electronically controlled rail valves.Te mechanically driven uel pumps havemultiple plungers in each block and run,due to gear wheels, at a higher speed thanthe engine. Tey have throttle control attheir inlets. Heated heavy uel oil isdelivered to the uel injectors at a supply pressure o about 1000 bar.

Servo oil is drawn rom the enginelubrication system, and is delivered by axial

piston-type pumps at pressures up to 300 bar.Te Wärtsilä R-flex unctions are

governed by Wärtsilä’s flexible and ully scalable unied control system (UNIC).Te master input comes rom the crank angle sensing system, which providesthe crank position and needed speedinormation to the control system.

High efciencyTe high efciency and simplicity o the Wärtsilä R-ex35 and R-ex40 enginesis the result o combining the R-ex

system itsel with the engine-driven uel

and servo oil pumps on all Wärtsiläcommon-rail two-stroke engines.

Te Wärtsilä R-ex system aords widetuning opportunities or optimizing theengine to match the vessel’s anticipatedoperational prole. Already establishedas alternatives to the standard tuningare Delta uning and Low-Loaduning, which provide reduced uelconsumption in the mid- and low-loadranges o operation (see Figure 1).

For example, consider a handysize bulk carrier equipped with a 6-cylinder WärtsiläR-ex35 engine and a load prole o 2500 running hours per year at 85% load,

2000 running hours per year at 75% load,and 1500 running hours per year at 50%load. When Low-Load uning is selected,the engine can save up to 1% in uelconsumption compared with the standardtuning.

For standard tuning rom a WärtsiläR-ex35 or Wärtsilä R-ex40 engine,the utilization o high perormance turbochargers is an essential part o the tuningphilosophy. In combination with theexible exhaust valve activation, thepart-load characteristic is optimized and

oers advantageous uel savings o around1% to 2% depending on the load prole,compared to conventional tuningphilosophies.

Direct drive o the uel pumps and servooil pumps also gives uel cost savings.Tese pumps consume some 1 to 2% o the engine’s power at MCR. For the6-cylinder Wärtsilä R-ex35, this wouldmean around 80 kW at MCR, and or the6-cylinder Wärtsilä R-ex40 around100 kW. I they were to be powered by electric motors, the equivalent energy

plus losses rom the lower efciency o

Table 1 – Principal particulars of the new Wärtsilä small-bore low-speed engines.

Engine type Wärtsilä RT-flex35 Wärtsilä RT-flex40

Cylinder bore, mm: 350 400

Piston stroke, mm: 1550 1770

Power/cylinder, R1 MCR, kW: 870 1135

Speed range, R1–R4, rpm: 167–142 146–124

Brake mean efective pressure, BMEP at R1, bar: 21.0 21.0Mean piston speed at R1, m/s: 8.6 8.6

Number o cylinders: 5 to 8 5 to 8

Power range, R2–R1, kW: 3475–6960 4550–9,080



WÄRTSILÄ TECHNICAL JOURNAL 01.2010

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electrical drive would need to be providedby auxiliary engines. For the 6-cylinder Wärtsilä R-ex35 it can be estimatedthat the uel savings are around 0.5%.

With the above engine’s load prole, 450MWh per year would eventually needto be provided by the auxiliary enginei electrical pump drives were used.

otal uel savings o 2.5% to 3% areachievable through the combination o thetuning opportunity, the high perormanceturbo charger with optimized exhaustvalve activation, and the direct driven ueland servo oil pumps. For the mentionedload prole, this results in savings o around 115 tonnes o heavy uel oil peryear. Tis gives cost savings o around

USD 70,000 per year, assuming a priceo USD 600 per tonne or heavy uel oil.

In summary, there are signicant savingsin liecycle costs to be obtained by optingor the Wärtsilä R-ex35 and Wärtsilä

R-ex40 engines in small and medium-sized ships powered by two-stroke engines:

■ Few cylinders or low maintenance costs ■ Low uel consumption as standard

or low operating costs ■ Delta uning or Low-Load uningor urther reduced uel costs

■ Direct propeller drive with xed-pitch propeller or high propulsionefciency, or with controllable-pitchpropeller or high manoeuvrability

■ Engine-driven uel and servo oil pumpsor minimum electrical demand.

ApplicationsTe application range or the WärtsiläR-ex35 and R-ex40 engines is

quite broad as already mentioned.Te global eet o handysize and

handymax bulk carriers consists o some3900 vessels. Tey have a typical speed inthe range o 13.5–15 knots. Consider the

case o a typical handysize bulk carriero 30,000 dwt. Its principal particulars

could be: ■ Length overall = 178.0 m ■ Length bp = 170.0 m ■ Beam = 27.6 m ■ Draught = 10.2 m ■ Speed = 12.2 knots ■ Main engine: A 6-cylinder WärtsiläR-ex35, 5220 kW at 167 rpm

■ Daily uel consumption at85% load = 18.33 tonnes

I we consider also the application o these new, compact engines in small

container vessels (less than 1000 EU),the global eet consists o about 1100vessels. Teir typical speeds are in therange o 16–19 knots. An 800 EU vesselcould have the ollowing particulars:■ Length overall = 140.0 m

■ Length bp = 132.0 m ■ Beam = 21.8 m ■ Draught = 7.4 m ■ Speed = 17.5 knots ■ Main engine: A 6-cylinder WärtsiläR-ex40, 6810 kW at 146 rpm

■ Daily uel consumption at

85% load = 23.77 tonnes

Another application is or Handysizeand Handymax tankers. Te global eetconsists o about 2400 vessels. Teirtypical speed is in the range o 14-15knots. An 35,000 dwt product tankercould have the ollowing particulars:

■ Length overall = 176.0 m ■ Length bp = 169.0 m ■ Beam = 29.8 m ■ Draught = 10.6 m ■ Speed = 15.0 knots

■ Main engine: A 7-cylinder WärtsiläR-ex40, 7945 kW at 146 rpm

■ Daily uel consumption at85% load = 27.13 tonnes

First ordersTe rst Wärtsilä R-ex35 engine is dueto be delivered in mid 2011, while the rst Wärtsilä R-ex40 engine is planned by the end o the rst quarter 2012.

Te rst order or ve 6-cylinder Wärtsilä R-ex35 engines is already conrmed. YMD has signed a contract

with Ningbo Donghai Shipping Co Ltd todeliver the engines or ve new 17,000 dwtchemical tankers. Te delivery o the rst o the ve engines is scheduled or August 2011.

Fig. 3 – Tuning opportunities and break specific fuel consumption (BSCF)

of the Wärtsilä RT-flex35.

Fig. 4 – Turbo-charging system and supply pump unit of the Wärtsilä RT-flex35.

b s f c , g / k W h

40% 50% 60% 70% 80% 90% 100%

load

Wärtsilä RT-flex35 R1 (Tier II)

182

180

178

176

174

172

170

168

166

Wärtsilä RT-flex Standard Wärtsilä RT-flex Delta Wärtsilä RT-flex Low-load

propulsion systems small vessels

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