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adjustments to achieve greater engine bal-ance and improved thermal efficiency.

A key functionality of the ME system isthe capability to vary both fuel injectiontiming and compression ratio using com-puter controlled actuators to determine theprecise timing of fuel injection and valveopening and closing. This permits continuedengine balancing at any operational profile,providing optimum pmax pressures whilereducing SFOC.

Wärtsilä’s RT-flex series use a commonrail system that permits complete control offuel injection timing, rate of fuel flow, fuelpressure and timing of valve operation. Anoption for the company’s electronic two-stroke engine, the RT-flex series, is anIntelligent Combustion Monitoring (ICM)system which continuously evaluates firingpressure data from all cylinders in order toproperly time fuel injection and valve oper-ation and provide ongoing engine balancingto optimise reduced fuel consumption. Thegood news is that ICM system can be retro-fitted to any older mechanical two-strokeengine.

The ICM system incorporates technolo-gy originally developed by ABB as theCylmate system, pioneered in the early2000s. In two-stroke engine testing con-ducted in February 2007 to verify the rela-tionship between pmax and SFOC, ABBincorporated a highly accurate, KRAL fuelmass flow meter. The test verified that witha 10 bar increase in pmax, SFOC wasreduced 2.2% – a relationship later mir-rored in test data reported by MAN Diesel.

Fuel degradation trend threatensefficiency gains

Rugged as they are, modern two-strokemarine engines remain subject to the capri-cious whims of fuel quality; with qualityexponentially deteriorating in recent years -the outlook is not hopeful. A survey con-

Faced with continued high fuelprices amidst depressed rates in a witheringglobal economy, owners are keen to adoptstrategies which keep balance sheets fromhemorrhaging red ink. Most, if not all ofthese common sense measures are outlinedin the IMO’s 2009-issued Ship EnergyEfficiency Management Program (SEEMP)guidelines that become mandatory for allvessels on January 1, 2013 and aim toreduce fuel consumption rates, which inturn, reduces CO2 emissions. Interestingly,although less CO2 is generated per one tonof cargo per mile from shipping comparedto all other forms of transportation, largemarine vessels still account for anywherefrom 4- 6% of so-called ‘greenhouse’ emis-sions globally.

The key to a successful SEEMP, thememo states, is planning on a vessel by ves-sel basis, followed by management improve-ments on the company level and the settingof specific, albeit private internal goals toachieve specific fuel consumption reductiontargets.

Most of the recommendations are immi-nently practicable, such as: weather routing,‘just-in-time’ scheduling, speed optimisation(better known as eco-speed), optimum trim,ballast and propeller configuration, properhull cleanliness and improved cargo han-dling.

Buried in section 4.25 of the memo isthe statement, ‘in particular, the new breedof electronic controlled engines can provideefficiency gains’ - a phrase grossly under-stated in view of decades of developmentand advancement made by the engine mak-ers MAN Diesel and Wärtsilä.

Increased pmax for reduced fuelconsumption

The primary objective of electronicengine control is to achieve optimum firingpressure with reductions in fuel consump-

tion rates per unit of power produced. Intheir research efforts, MAN Diesel andWärtsilä have determined that for every barincrease in peak firing pressure (pmax), spe-cific fuel oil consumption (SFOC) is reducedapproximately 0.25%. Hence, with a pmaxincrease of 6 bars, SFOC is reduced by1.5% – a number that can mean significantsavings annually for fleet operators.

First introduced in February 2003,MAN Diesel’s ME engine was–essentiallyan electronic version of the MC series thataimed to optimise peak firing pressure(pmax) at all load ranges thereby reducingSFOC and CO2. A first step is ‘auto tuning’,where firing pressure from each cylinder ismonitored by a sensor, the data sent to anonboard processor with software that inter-prets the results and formulates an appro-priate response which makes operational

Ralph Lewis looks at official effortsto codify measures for moreefficient marine propulsionincluding an advanced petroleumtechnology

ADVANCING PROPULSION EFFICIENCY

Pmax Increase with PRI TechnologyThe measurement of two combustioncurves on a MAN Diesel S70MC-C showsthe improvement in peak combustionpressure when the engine is operating onPRI-27 treated fuel. For bothmeasurements, the engine was running atidentical speed and loads

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PROPULSION EFFICIENCY

In April 2007, MANDiesel engineersconducted a test ofPRI-RS thermal sta-bility fuel treat-ment on a Holeby5L21/31 engineunder the MarpolAnnex VI protocol.The test verifiedthat PRI-RS reducesCO, THC and PM,and establishedcombustion effi-ciency improve-ment with an eleva-tion in peak com-bustion pressure(pmax)

ducted by DNVPS in early 2011 confirmsfuel quality issues are rapidly on theupswing. Of those responding to the survey,80% complained of ‘off-spec’ fuel, and ofthose, 44% classified the problems as ‘seri-ous’. The greatest complain was ‘filter clog-ging’, reported by 64% of respondents. Thiswas followed by excessive sludge issues(48%), fuel pump sticking and seizures(40%) and broken ring problems (19%).

Speaking before the InternationalBunker Conference in Copenhagen in April2011, DNVPS Managing Director TonyMorten Wetterhaus warned of more prob-lems ahead: ‘Over the next two or threeyears, we are expecting more fuel qualitycases due to increased blending activities inthe supply chain to meet the greater needfor low sulfur fuel oil (LSFO) products.Unregulated blend components will remaina key cause to such problems.’

Ironically, the increased use of lowerquality, ‘waste’ distillates as cutter stock isan unintended consequence of laws man-dating ultra-low sulfur diesel (ULSD) fuelproduction for onshore automotive use. The

fuel is produced through a method knownas hydro-desulphurisation – one that alsouses aluminum/silicon catalysts in the fuelcracking process. Also known as ‘hydro-treatment’, this process yields lower end dis-tillates of little commercial value - lightcycle oil and slurry oil.

These distillates can also become heavi-ly contaminated with spent cat fines thathave sloughed off during the refiningprocess – with a 20+% increase in cat finecontent in marine fuels over the past threeyears as the number of hydro-treatmentunits has grown to meet ULSD demand. ‘Sofar this year, issues with excessive cat fineshave been our greatest challenge,’ saysSoeren Esbensen, MAN Diesel Head ofOperations for low speed diesels.

Further aggravating the problem is theexpansion of ECAs requiring use of 1.0%low sulfur fuel oil (LSFO) that is complex toextract and very expensive. Consequently,far too few of these units exist to begin tomeet the requirements for marine consump-tion – a reason why use of inferior distillatesas cutter stock for LSFO will predominatefor years to come.

Many vessel owners have attempted toovercome these issues with marine fueltreatment additives. Section 4.27 of theMEPC memo even suggests the use of fueladditives to improve propulsion systemmaintenance. However, among the widerange of offerings from marine fuel treat-ment manufacturers, only one product hasemerged that has actually been verified byan engine maker to safely improve combus-tion and reduce emissions under the verystrict testing protocol of Marpol Annex VI.

Advanced Fuel TreatmentTechnology

PRI believes that its thermal stabilitychemistry provides the answer – with resultsproven over just two days of testing at theMAN Diesel engine emissions certificationfacility in Denmark in April 2007. The teston a MAN Diesel 5L21/31 engine verifiedthat with PRI treatment of the fuel, averagepmax for all loads (100%, 75%, 50%, 25%and 10%) averaged a dramatic increase of5.2 bars. At loads of 75% and less, averagepmax increase with PRI increased 5.8 bars –a reduction in SFOC of 1.45%.

Combustion improvement was clearlyverified in the emissions data. At all loadranges, application of PRI chemistry result-ed in significant reductions in carbonmonoxide (CO), total unburned hydrocar-bons (THC) and particulate matter (PM).

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September 2012 • MER • 37

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tion. PRI products for heavy fuel oil arealso formulated with industrial sludge dis-persants which help recover lost fuel valuewith sludge reductions in the 35-to-50%range.

Although the concept is new to themarine industry, producers of aviation fuelhave been researching thermal stabilityissues for decades. Aviation fuels withmoderate or poor thermal stability cancreate hot spots on the combuster wall ofjet engines, leading to cracks and prema-ture engine failures – not a good thing at30 000 ft. Carbon deposits from fuels withmoderate to poor thermal stability canalso impinge on turbine blades and sta-tors, causing erosion.

In the onshore automotive sector, thefirst thermal stability additives began toappear following passage of the US FederalClean Air Act in 1977 – a law which man-dated the use of the technology in all gaso-line sold in the US. The EPA justificationfor the mandate was clear – cleaner enginesoptimise combustion efficiency, minimizingemissions products.

No such mandate exists for marinefuels. Worse yet, the ISO 8217 standard is ashadow of the much tougher standardsmandated for refiners of onshore automo-tive fuels. ‘Fueling an innovative electronicmarine diesel engine with an inferior quali-ty fuel is like fueling a Formula One carwith 87 octane gasoline,’ says BlakeDavidson, cfo of Power Research Inc. ‘It isone step forward in marine propulsion tech-nology, but two steps backward in efficien-cy gains.’

‘When we launched Power ResearchInc. in the mid-1980s, we saw a situationwhere fuel standards in commercial ship-ping lagged far behind those of onshoreindustries,’ Davidson says. ‘We also realisedthat the existing fuel treatment ‘remedies’for marine fuels were grossly insufficientcompared to those developed for automo-tive fuels. PRI thermal stability technologynot only dramatically addresses these issues– but it is saving our clients millions of dol-lars annually at a time when they need theseefficiencies the most.’ MER

The version of the PRI fuel treatmentchemistry for distillate fuels, PRI-D, hadpreviously been verified in testing by theSouthwest Research Institute in Texas,under the rigorous EPA Heavy Duty Dieselemissions testing protocol. In this testing,the chemistry provided an increase in horse-power with a reduction on brake specificfuel consumption, and reductions in CO,THC and PM.

Manufactured by Houston-basedPower Research Inc, PRI technology isincorporated into three products – PRI-RSand PRI-27 for heavy marine fuels – andPRI-D for marine distillate fuels. The tech-nology can be found onboard the vessels ofclose to 200 commercial shipping clientsworldwide, with continued shipboardapplication re-confirming the test standengine results.

In one example, a container vessel oper-ating on a fixed schedule consuming RMG380 fuel has been continually monitoringPRI-27 performance on a two stroke MANDiesel 7S70 MC-C. With the PRI-27 ther-mal stability additive, pmax has increasedan average of 3.89 bar, providing an SFOCreduction of almost 1% – $147 000 annu-al savings in fuel cost. Coupled with recov-ery in lost fuel value from reduced sludgeprecipitation, total annual savings total$174 000.

In a four-stroke engine application, adiesel electric cruise ship operating with sixWärtsilä 46/50DF engines is showing anacross the board average increase in pmaxof 6.2 bars with PRI-RS, resulting in anSFOC reduction of 1.55%. Based on pres-ent fuel prices and consumption rates, thevessel saves $312 000 annually. Sludge datafrom the vessel confirms a 40% reduction insludge with PRI-RS, recovering sufficientfuel value to more than cover the overallinvestment in the chemistry.

The functionality of PRI-RS, PRI-27and PRI-D relies on product capability toelevate the thermal stability of fuels. Inbasic terms, fuels with high thermal stabili-ty are less prone to producing unburnable,high carbon weight structures that formduring the coke ignition phase of combus-

The capability of PRI fuel treatment technology to significantly reduceparticulate matter from marine engines is evident in photos of particulatefilters used during a 2007 MAN Diesel test of the product. At left is a filterused during the untreated fuel portion of the test. At right is a photo of afilter used during the PRI treated portion of the test – both readings taken atidentical loads.

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