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Theoretical Investigation of an Optimized Turbo Compound System applied on a Marine 2-Stroke Diesel

Engine Nikolaos Sakellaridis, Speaker

[email protected]

Efthimios Pariotis

Dimitrios Hountalas

National Technical University of Athens

School of Mech. Eng.

I.C Engines Lab.

EEinS2015 - International Conference “ENVIRONMENT & ENERGY in SHIPS 2015”

Contents

• Background and Motivation

• Fuel Consumption Reduction & Waste Heat Recovery Overview

• Simulation model description and validation

• Turbocompounding System Optimization: Results and Main Findings – Power Turbine Speed Variation @ 85% Load

– Turbocharger Turbine Size Variation @ 85% Load

– SOI advance @ 85% Load

• Conclusions


Background and Motivation

• Maritime Transport an important sector of global transport.

• 2-Stroke Diesel Engine is the primary mover & energy consumer (85% of fuel)

Efficient

Reliable

High Power Density

Cost effective (Operation using HFO)

• Further reduction in fuel consumption necessary:

Environmental regulation/ Greenhouse Gas reduction

Rising fuel prices

Possible measures for Fuel Consumption reduction?


Contents







• Conclusions


Fuel Consumption Reduction& Waste Heat Recovery Overview (1)


Measures to reduce fuel consumption

Examples Advantages Disadvantages

Operational Slow Steaming Optimal routing/ loading Diagnosing/ Reducing energy losses

Simple Implementation Low cost Significant benefit

× Impact on delivery time × Impact on engine

subsystem due to off design operation

× Often require technical modifications

Technical Engine subsystem/ Combustion optimization Friction reduction Vessel hydrodynamics Alternative fuels

Waste heat recovery

Applicable in wide engine operating range

Specific NOx and SOx reduction along with CO2

× Pay back period often unfavorable

× Limited application on existing vessels

• High Potential : About 50% of fuel heat rejected in large 2-stroke Diesel Engines • Exhaust gas : Most significant, high temperature waste heat ? Technical Implementation ? Actual Benefit ? Impact on engine operation

Fuel Consumption Reduction & Waste Heat Recovery Overview (2)


Power Generation

Rankine Bottoming Cycle: Complete exhaust gas powered Rankine system (including boilers, expander, condensers etc)

Water or organic medium

Large BSFC benefit Minimal interaction

with engine

× Size × Complexity/ Cost × Engine Back- Pressure

Turbo-Compounding: Expand a portion of exhaust gas in a power turbine

Low cost

× Lower BSFC benefit × Limited application on existing

vessels

Exhaust Heat

Recovery

Vessel Heat Loads

Exhaust side boilers Steam Fuel Pre- Heating

× Engine Back- Pressure

Aim of Current Work

? Max. Theoretical benefit in practical applications ? Methodology to determine optimal power turbine/ Engine settings. ? Application in existing engines ? Impact on engine operation

Contents







• Conclusions


Model description & validation Description


Simulation Tool GT- Power

Compressor/ Turbine Meanline (0-D) models using measured geometry data. Implemented as user subroutines in the code

Combustion Built- in predictive combustion model (DI- Jet). Calibrated using cylinder pressure data acquired by present research group

Model Inputs

Ambient Conditions

Fuelling rate

Start of Injection (SOI)

Temperature after A/C

Engine/ Turbine/ Compressor main geometry data

Power turbine speed

Engine rotational speed

Model Outputs

T/C performance • Scavenging & Exhaust

receiver pressure • TC speed • Turbine inlet & Outlet

temperature • Etc...

Power Turbine Output

Engine Performance • Cylinder pressure • Heat Release • Start of Combustion • Power Output • BFSC • Etc...

Model description & validation Validation


40 60 80 100Load [%]

6000

8000

10000

12000

14000

16000

18000

T/C

speed

[rp

m]

T/C speed sim.

T/C speed exp.

40 60 80 100Load [%]

1

2

3

4

Pre

ssure

[bar]

Pscav sim.

Pscav exp.

Pexh sim.

Pexh exp.

40 60 80 100Load [%]

0

25

50

75

100

125

150

175

200

Pre

ssure

[bar]

Pmax sim.

Pmax exp.

Pcompression sim.

Pcompression exp.

40 60 80 100Load [%]

160

170

180

190

200

210

220

230

240

BS

FC

[g/k

Wh]

BSFC sim.

BSFC exp.

Power sim.

Power exp.

0

5000

10000

15000

20000

Bra

ke P

ow

er

[kW

]40 60 80 100

Load [%]

0

100

200

300

400

500

600

700

800

Tem

pera

ture

[0K

]

Tinlet sim.

Tinlet exp.

Toutlet sim.

Toutlet exp.

Model Validation

Comparison of models prediction vs exp. Data ( official engine shop tests) • Good predictions over a wide range of

loads • Engine and T/C performance predicted

well Reliability of engine and T/C model

Test Case: 2-Stroke Marine Diesel

Bore 700 mm

Stroke 2800 mm

Connecting Rod Length 2850 mm

Cylinders/ Turbochargers 6/2

Contents







• Conclusions


Turbocompounding System Optimization: Results and Main Findings

Power Turbine Speed Variation @ 85% Load


Variation of Power turbine (PT) speed

• Power turbine (PT) added to engine model. • Investigation conducted for various power turbine sizes from 0.03-0.16 . • Power Turbine Size= mass flow through PT/(mass flux/es through T/C turbine/s) • For practical applications : Variation of reduction gear ratio, generator speed


Power Turbine Speed Variation @ 85% Load


Optimum

30000 40000 50000 60000 70000 80000Power Turbine Speed [rpm]

-0.75

-0.5

-0.25

0

0.25

0.5

ΔBSFC

[g/k

Wh]

Power/ TC turbine flow capacity ratio

0.03

0.05

0.07

-4.1 -6.0

-1.2

0.4

6.4

-7.7 -8.0 -6.7

-0.3

-10-8-6-4-202468

TCspeed

Pmax Eng.Power

TotalPower

Texh Pscav Pexh Airflow

BSFC

Para

mete

r va

riati

on

wit

h

Tu

rbo

co

mp

ou

nd

ing

[%

]

Evaluate: • Brake Specific Fuel consumption benefit (ΔBSFC): BSFC of turbocompound System –BSFC of reference engine • Constant fuelling rate • Define optimum • Impact on engine operation at the defined optimum

Conclusions: • Small benefit due to engine performance degradation • Reduction in Pscav, Pmax , Pexh and Air flow. Increase in Texh • Optimal PT speed reduces with increasing PT size Engine tuning to recover engine performance and maximize benefit???

1 2

1

1

2 1 2 2 2

2

3

3

Performance compared to reference at optimum [% Variation]

PT size

Contents







• Conclusions


Turbocompounding System Optimization: Results and Main Findings T/C Turbine size variation @ 85% Load


Variation of Turbocharger Turbine (T/C) Size

• Reduction of T/C turbine flow area Increases scavenging pressure and exhaust receiver pressure • Power turbine speed for every size at the optimal value, determined from previous step • In practical applications : Matching a smaller turbine, use of a nozzle ring of reduced flow area.

Turbocompounding System Optimization: Results and Main Findings T/C Turbine size variation @ 85% Load


Evaluate: • For every PT size is determined the optimal T/C turbine size • Impact on engine operation at the defined optimum

Conclusions: • Increased benefit compared to only optimizing PT speed (≈ x 2) • Optimal performance at larger PT size (0.09) • Significant reduction in air flow and increase in Texh

Optimum

0.88 0.92 0.96 1T/C turbine size

-1.25

-1

-0.75

-0.5

-0.25

0

0.25

0.5

ΔBSFC

[g/k

Wh]

Power/ TC turbine flow capacity ratio

0.07

0.09

0.11

-6.1 -7.5

-2.1

0.8

15.1

-8.8 -7.8

-14.7

-0.6

-20

-15

-10

-5

0

5

10

15

20

TCspeed

Pmax Eng.Power

TotalPower

Texh Pscav Pexh Air flow BSFC

Pa

ram

ete

r va

ria

tio

n w

ith

T

urb

oco

mp

oun

din

g [%

]

1

2

3

1

2

3

3


PT size

Contents







• Conclusions



SOI advance @ 85% Load


Start of Injection (SOI) advance

• For every power turbine size: Power turbine speed and optimal T/C turbine size at optimal values determined in previous steps

• Earlier injection/ Combustion to reach firing pressure of reference engine (without Turbocompounding) • For practical applications : Increase of VIT system rack.

-80 -40 0 40 80 120Crank Angle Degrees [ o ATDC]

0

40

80

120

160

200

Pre

ssu

re [

ba

r]

Reference engine at 85% load

Power Turbine size=0.13, 85% engine load

Reference pressure


SOI advance @ 85% Load


Evaluate: • Define optimal PT size for max ΔBSFC • Impact on engine operation at the defined optimum

Optimum

0 0.04 0.08 0.12 0.16Power turbine flow capacity/ T/C turbine flow capacity

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

ΔBSFC

[g/k

Wh]

-9.9

0.0

-0.9

2.8

20.7

-15.4 -14.4

-21.7

-2.5

-25-20-15-10-505

10152025

TCspeed

Pmax Eng.Power

TotalPower

Texh Pscav Pexh Airflow

BSFC

Para

mete

r va

riati

on

wit

h

Tu

rbo

co

mp

ou

nd

ing

[%

]

Conclusions: • ≈ 4.4 g/kWh benefit in BSFC • Degradation in engine power very small due to Pmax= Pmax, reference • Very significant reduction in air flow and corresponding increase in Texh Exhaust temperature and sooting

combustion may limit benefit in practical applications!!

1

2

3

1

2

3

3


PT size

Contents







• Conclusions


Conclusions


Impact of Turbocompounding on Marine 2-Stroke engine operation: • Reduction of engine power output, scavenging, exhaust, peak firing pressure and

T/C speed. Power turbine output must compensate for engine power reduction. • Reduction in air flow and increase in exhaust temperature . Manufacturer

limitations must be respected in practical applications.

Measures to maximize the benefit of turbocompounding: • Optimize power turbine speed. Optimal power turbine speed reduces with

increasing turbine size. • Reduce T/C turbine effective flow area to compensate the reduction in scavenging

pressure and increase PT expansion ratio. • Advance SOI to reach the max permissible pressure levels (pressure of reference

engine at the same load). Benefit of a turbocompound engine optimized using the aforementioned methodology ≈ 4.4 g/kWh (2.5% ) ΔBSFC at 85% load.


Theoretical Investigation of an Optimized Turbo Compound System applied on a

Marine 2-Stroke Diesel Engine

Nikolaos Sakellaridis, Speaker email [email protected]

Thank you for your attention!

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