Technical information

The Power2® performance packageNOx down, power up, fuel down

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Power2 two-stage turbocharging Leading edge technology for large engine turbochargers.

Driven by engine builders’ demands for ever lower levels ofharmful emissions and greenhouse gases combined with ever higher levels of power density and fuel efficiency, Power2takes turbocharger performance into a new range.

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Power2 is capable of producing pressure ratios up to 12,compared with up to 6 for the best single-stage turbochargers.

Emissions imperativeThe launch of Power2 two-stage turbocharging comes as thelarge engine industry gears up for its greatest emissions challenges. A major focus is limitations on oxides of nitrogen(NOx ) due in the middle of this decade. They demand reduc-tions as severe as 80 to 90 percent compared with the IMOTier I requirements. At the same time, governments all roundthe world have committed themselves to reducing greenhousegas emissions, including carbon dioxide (CO2), the majorcomponent of engine exhaust gases.

Boosting efficiency, boosting power Combining charge air boost pressure of two-stage turbo -charging with outstanding turbocharger efficiency can bringsubstantial benefits – improved engine fuel efficiency. Thistranslates into reduced fuel bills for the engine operator,reduced emissions of the greenhouse gas CO2 and reducedfossil fuel depletion. In addition, the greater availability ofcharge air offers potential to raise engine power density.

Miller enabler Significantly, Power2 two-stage turbocharging is already anacknowledged “enabling technology” of the Miller Cycle, aningenious method of cooling combustion air to substantiallyreduce NOx formation in internal combustion engines. It isalready in use on large diesel engines designed to meet cur-rent rounds of emissions legislation in conjunction with highpressure single-stage turbocharging. To meet the stringentfuture stages of NOx legislation, turbocharging pressure ratioswill be needed in the range Power2 is already producing.

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Enabling Miller Miller Cycle versus the NOx-SFC trade-off.

Taming the trade-offPower2 two-stage turbocharging is set to be a major factor in tackling one of the dilemmas of engine emissions reduction– the trade-off between NOx formation and specific fuel consumption (SFC). The “NOx-SFC trade-off” reflects the factthat NOx formation decreases with lower combustion temper-atures while fuel efficiency increases with higher combustiontemperatures. On diesel engines, a widespread measure hasbeen to reduce combustion temperatures and hence NOx for-mation by fuel injection rate shaping. Thus, a fuel consump-tion penalty is incurred in the interests of lower NOx emissions.The Miller Cycle, however, is capable of shifting this compro-mise into a new, far lower range.

Miller Cycle principleOn four-stroke engines, substantial cooling of engine intakeair is achieved by advancing the inlet valve closing timing.This induces expansion and hence cooling in the intake air onthe induction stroke. On two-stroke engines, a similar effectcan be achieved by varying exhaust valve closure. The coolingeffect is capable of eliminating the combustion temperaturepeaks responsible for over 90 percent of NOx.

Power2 pressure ratios versus shorter inductionThe earlier intake valve closing means that, without turbo -charging countermeasures, only a reduced mass of air couldenter the combustion chamber in the time available. Theresult would be reduced engine output and poor response toload changes. Higher turbocharging pressure ratios compen-sate the shorter induction time to avoid combustion air defi-ciency.

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Shifting the curve – fuel consumption and NOx reduction potentialusing two-stage turbocharging to achieve strong Miller Cycles on further developed diesel engines.

Early Miller Cycle and standard induction at the moment of inlet valve closure.

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ABB Turbocharging’s Power2 concept uses two turbochargersin tandem to create pressure ratios higher than the best sin-gle-stage turbochargers.

Systems under development consist of two specially designedturbochargers of different sizes connected in series. They are tuned as a system to give favorable thermodynamic andmechanical behavior. Their performance is carefully chosen to give the level of air delivery required by the specific appli -cation.

The turbine of the smaller turbocharger is located upstream of the turbine of the larger unit in the exhaust gas flow from the engine. On the air side, the flow from the compressor of thelarger turbocharger is fed into the compressor of the smallerturbocharger.

How it worksThe Power2 two-stage turbocharging principle.

Intercooling between the two compressor stages reduces thetemperature and the volume of the air after the first stage turbocharger which allows the second stage turbocharger tobe smaller, making the total system more compact.

This arrangement readily produces the high turbochargingpressure ratios needed to create very strong Miller Cycles onfour-stroke medium-speed diesel engines.

Achieving the 80 percent NOx reduction required by IMO Tier IIIcompliance in ECAs without aftertreatment would reduce thefirst costs and operating costs of an engine system. Power2can be a part of this solution.

Schematic of ABB Turbocharging’s Power2 two-stage turbochargingsystem. An intercooler allows the second turbocharger to be more compact.

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Engine control with Power2Air management.

To adapt charge air output to demand from the engine under a full range of load and speed conditions, Power2 two-stageturbocharging can be used with familiar turbocharger controloptions. Their control organs can be integrated into overridingelectronic engine and powertrain management systems.

Advanced control for Variable Miller CyclesThe strong Miller Cycles which Power2 can enable assume an engine operating at its best point for power and /or fuelconsumption and/or emissions, i. e. its maximum continuousrating or “MCR”.

However, in many applications on land and sea, engines areexpected to “follow the load”. At sea this is the case with bothpropulsion systems and generator sets feeding the onboardelectrical consumers. On land variable load applicationsinclude: locomotive engines; travel and working functions onoff-highway mobile equipment; diesel and gas engines drivingcompressor sets; generator sets feeding variable load con-sumers.

At low loads or during start-up, later inlet valve closing timingis needed for stronger Miller Cycles. They serve to avoidsmoke emissions and poor transient response.

VCM With its Valve Control Management (VCM®) system, ABBTurbocharging can provide a method of adapting the MillerCycle to lower loads via the stepless adjustment of inlet valvetiming and lift. VCM is also capable of varying the output ofthe two turbochargers via its effect on the engine’s gasexchange. The system achieves management of valve timingand lift by interposing a high pressure oil chamber into theengine valve train between the valve and its mechanical actu-ation system. A solenoid valve varies the filling of the chamberwith engine lube oil pressurized by a camshaft actuatedpump. The pump also feeds a brake unit that controls the setting velocity of the valve to limit forces when the valve contacts its seat.

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ABB TurbochargingA unique partner for advanced engine components.

Power2 two-stage turbocharging is a major part of ABB Turbocharging’s growing portfolio of products and services for engine builders and engine end users. They share thecommon theme of optimizing the performance, economy, reliability, availability, life cycle costs and not least the exhaustemissions of diesel and gas engines – and hence ships, power plants, mobile equipment and locomotives fitted withABB turbochargers.

Proactive solutions For ABB Turbocharging this means proactively addressing theneeds and concerns of both engine builders and engine end users to devise solutions which are both effective andeconomic.

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Complementary technologiesPower2 is one of two complementary building blocks ABB Turbocharging can offer engine builders as a uniquepartner to address what are presently their major concerns:– Compliance with the strict limitations on emissions of oxides

of nitrogen (NOx ) from engines on land and at sea due to beimplemented in the middle of the present decade

– Increasing fuel efficiency in the face of the steady rise in theprice of fossil fuels and international agreements governingemission of the greenhouse gas carbon dioxide (CO2)

Power2 and VCM interactionMeshing perfectly with Power2 two-stage turbocharging isABB Turbocharging’s Valve Control Management (VCM)system for the progressive adjustment of valve timing and lift.These complementary technologies represent essentialenablers of Variable Miller Cycles on large four-stroke engines.

On the one hand Power2 provides the high turbochargingpressure ratios and efficiencies needed for the very strongMiller Cycles required to realize high NOx reduction percent-ages.

On the other hand VCM allows the engine’s gas exchange to be optimized over a full range of engine operating conditions,hence allowing the effect of the Miller Cycle to be varied.

Via its effect on engine gas exchange VCM is also an effectivemethod of varying the output of the two turbochargers in thePower2 system.

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Emissions complianceIMO Tier III and EPA Tier 4 are typical of the emissions legislation to be enacted in the middle of the present decadeaffecting engines with outputs over 500 kW.

IMO Tier III The third stage of marine engine emissions legislation issuedby the International Maritime Organisation and due in 2016builds on IMO Tier II. In 2016 the generally applicable 20 per-cent reduction in NOx emissions vis-à-vis IMO Tier I (intro-duced 2000) continues to govern NOx emissions on the highseas. However, IMO Tier III demands an 80 percent reductionin NOx emissions from vessels operating in Emissions ControlAreas, or “ECAs”.

ECAs are, broadly, coastal waters close to areas of populationor environmentally sensitive locations. ECAs already designatedare the complete East and West Coasts of the USA andCanada, straits like the English Channel, landlocked seas likethe Baltic and numerous port approaches.

EPA Tier 4 standardsEmissions standards issued by the USA’s Environmental Pro-tection Agency cover NOx emissions from water borne, mobileand stationary engines of all sizes used in a wide range ofapplications. Up to 2015, the EPA Tier 4 standard requiresNOx emissions to be reduced by around 90 percent comparedto the 2008 Tier 1 baseline.

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ABB Turbocharging Service network

ABB Turbo Systems LtdBruggerstrasse 71 aCH-5401 Baden/SwitzerlandPhone: +41 58 585 7777Fax: +41 58 585 5144E-mail: turbocharging@ch.abb.com

www.abb.com/turbocharging

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