Technical information

ABB TurbochargingThe Power2 miracle – NOx 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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Even in this early stage of its development, Power2 is alreadycapable of producing pressure ratios up to 8 and more, compared to 5.8 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 % compared with the first stagesof the leglisation involved. At the same time, governments all round the world have committed themselves to reducinggreenhouse gas emissions, including carbon dioxide (CO2),the major component of engine exhaust gases.

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.

Boosting efficiency, boosting power The charge air boost pressures two stage turbocharging canproduce also bring substantial benefits in terms of engine fuelefficiency. This translates into reduced fuel bills for the engineoperator, reduced emissions of the greenhouse gas CO2 andreduced fossil fuel depletion. In addition, the greater availabilityof charge air offers potential to raise engine power density.

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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 4-stroke engines, substantial cooling of engine intake air isachieved by shortening the opening period of the inlet valve.This induces expansion and hence cooling in the intake air onthe induction stroke. On 2-stroke engines, a similar effect canbe achieved by varying exhaust valve closure. The coolingeffect is capable of eliminating the combustion temperaturepeaks responsible for over 90 % of NOx.

Power2 pressure ratios versus shorter inductionThe shorter valve opening periods mean that, without turbo -charging countermeasures, only a reduced mass of air couldenter the combustion chamber in the time available. The resultwould be reduced engine output and poor response to loadchanges. Higher turbocharging pressure ratios compensatethe shorter induction time to avoid combustion air deficiency.

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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 singlestage 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 larger turbocharger is located upstream ofthe turbine of the smaller unit in the exhaust gas flow from the engine. Similarly, the output of the compressor of the largerturbocharger is fed into the compressor of the smaller turbo -charger.

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 on4-stroke medium speed diesel engines.

Achieving the 80 % NOx reduction required by IMO Tier IIIcompliance in ECAs without aftertreatment would reduce thefirst costs and operating cost of an engine system consider-ably. Computer simulations using ABB Turbocharging’s sophis-ticated software indicate that this is a realistic prospect.

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

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Power2 Control for variable MillerTwo stage turbocharging control options.

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, longer inlet valve openings areneeded than the short timings appropriate to strong MillerCycles. They serve to avoid smoke emissions and poor tran-sient response.

VCM With its VCM “Valve Control Management” 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 above the valve tolimit 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 VCM Valve Control Management system for the progressive adjustment of valve timing and lift.These complementary technologies represent essentialenablers of Variable Miller Cycles on large 4-stroke engines.

On the one hand Power2 provides the high turbochargingpressure ratios needed for the very strong Miller Cyclesrequired to realize high NOx reduction percentages.

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, due in 2011. In 2016 the generally appli-cable 20 % reduction in NOx emissions vis-à-vis IMO Tier I(introduced 2000) continues to govern NOx emissions on thehigh seas. However, IMO Tier III demands an 80 % reduction in 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 % compared tothe 2008 Tier 1 baseline.

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IMO NOx curves

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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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