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© 2010 Concepts ETI, Inc. All rights reserved.

ORGANIC RANKINE CYCLE TURBINEFOR EXHAUST ENERGY RECOVERY IN AHEAVY TRUCK ENGINE

Nick SharpCummins Turbo

Technologies Ltd.

Derek Cooper,Nick Baines

Concepts NREC


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© 2010 Concepts ETI, Inc. All rights reserved. 2

Outline

Context Development program• Organic Rankine cycle uses a

refrigerant working fluid that:Is heated by engine exhaust gasExpands through a turbineconnected (through gearing) to

the engine shaft• A novel turbine design is

required because: The operating conditions (speed,flow, pressure ratio, etc) are quitedifferent from those of

conventional turbochargerturbines The fluid properties of therefrigerant are different fromthose of air, exhaust gas, etc

• Investigate a range of turbinearchitectures to determinesuitability, i.e.

PerformanceSize / packaging

Manufacturability• Down-select to the most

promising solution• Detail design, manufacture, and

prototype test


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3© 2010 Concepts ETI, Inc. All rights reserved.

Design specifications

Turbine RotationalSpeed Gear Ratio

40k rpm 26.7:1

50k rpm 33.3:1

60k rpm 40.0:1

84k rpm 56.0:1

Turbine shaft speeds and gear ratios at B100 condition

Maximum efficiencySmall footprintMinimum shaft speed

Ideal Solution

• Turbine design point rotational speed is set by typical engineoperating speed and consideration of mechanical couplingbetween turbine and engine


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• Specific speed is auseful way tocharacterizeturbines

• There are good,experience-based,

rules• Design conditions

demand specificspeeds that are wellbelow those oftypical automotive

turbochargers

Turbine selection

Single stageturbine, 84k rpm

Single stageturbine, 40k rpm

Two stage turbine,84k rpm

Automotive turbo-charger typical

( )3 4Speed Volume flow rate

Specific speedSpecific work output

×=


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• Single stage radial turbine• Two stage axial turbine• Single stage axial turbine

• In each case, consider a range of speeds from 40,000-84,000 rpm

Conceptual designs


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• Efficiency increases withspeed of rotation

• Size decreases with speed

of rotation• Even at the highest speed,

the ratio of passage heightto rotor radius is very small

Single stage radial turbine


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• Blade height decreasesand tip radius increasesas turbine speed isreduced to maintainsimilar tip speeds

• Efficiency increases withspeed of rotation

• Significant change inwheel speed across bladespan: variable sectionblades are required for all

two-stage designs• Possible to design blades

to be flank-millable withsmall impact on efficiency

Two-stage axial turbine

84k rpm 60k rpm

50k rpm 40k rpm


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• Tip radius decreases andblade height increases withspeed

• Efficiency increases with

speed• Stator blades are transonic:

exit Mach number = 1.5 – 1.7• Constant section blades are

acceptable (reducesmanufacturing costs)

Single stage axial turbine


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0

5

10

15

20

25

30

35

40

40000 50000 60000 70000 80000 90000

T i p r a

d i u s

( m m

)

Turbine design speed (rpm)

Two-Stage Axial

Single-Stage Axial

Radial

0.6

0.65

0.7

0.75

0.8

0.85

0.9

40000 50000 60000 70000 80000 90000

A e r o

d y n a m i c e

f f i c i e n c y

Turbine design speed (rpm)

Two-Stage Axial

Single-Stage Axial

Radial

• Two-stage turbine has potential performance, but too complicated• Down-select to single stage axial turbine

Performance summary

Axial turbine architecture

is more competitive atlower turbine speeds


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• Bladed, con-di nozzle • Drilled and reamed conicalnozzle

Supersonic nozzle options


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• Better performance (+5 ptefficiency at maximum loadconditions)

• More expensive tomanufacture. EDM/ECM isrequired

• Throat width ≅ 1 mmDesign and performance isvery sensitive to manufacturingtolerancesTesting will be required toestablish final design

• Circumferentially non-uniformflow entering rotor makesperformance prediction difficult.

Some experience required• Cheaper to manufacture and

easier to hold throat areatolerances

• Design is compromised by size

envelope, and requires adifferent inlet duct arrangement

Supersonic nozzle options

Bladed, con-di nozzle Drilled, conical nozzle


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• Single stage architecture demands veryhigh flow turning, but this can bemanaged with proper aero design

• Shrouded rotor is required to reduce tipleakage losses, which have a largeimpact on efficiency in a small turbine

Rotor design


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• The ORC demands a unique turbine solution, and conventionalturbocharger turbine design has little relevance

• The turbine is highly loaded, with a supersonic nozzle• Two nozzle variants were developed to function with a common

shrouded rotor Full admission arc airfoil nozzlePartial admission drilled nozzle

• The turbine performance is very sensitive to rotor leakage flow andproper treatment of this flow is critical

• The airfoil nozzle turbine is predicted to achieve satisfactoryefficiency with proper sealing solutions

Conclusions

Documents

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