1

Optimization of the Molecular Structure of Low-Greenhouse-Gas-Emission Synthetic

Oxygenated Fuels for Improved Combustion and Pollutant Emission Characteristics of

Diesel Engines

C. T. Bowman, R. K. Hanson, H. Pitsch, D. M. GoldenDepartment of Mechanical Engineering

R. MalhotraSRI International

GCEP

2

Optimization of the Molecular Structure of Synthetic Oxygenated Fuels for Diesel

Engine Applications

C. T. Bowman, R. K. Hanson, H. Pitsch, D. M. GoldenDepartment of Mechanical Engineering

R. MalhotraSRI International

GCEP

3

Optimization of Synthetic Oxygenated Fuels(a.k.a The Oxyfuels Project)

C. T. Bowman, R. K. Hanson, H. Pitsch, D. M. GoldenDepartment of Mechanical Engineering

R. MalhotraSRI International

GCEP

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Presentation Outline

• Background and Motivation – Why Oxyfuels?

• Project Goals

• Research Tasks and Approach

• Results

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U. S. Combustion-Generated CO2 EmissionsTotal = 1631 x 109 kg C/yr (2005)

Electric Power Generation - 39%

Transportation33%

Industrial18%

Commercial4%

Residential6%

Automobile andLight Truck

62%

Heavy Duty Truck and Rail - 23%

Aircraft12%

Ship3%

EIA 2006

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U.S. Energy Consumption 2004

EIA, 2005

Natural gas, 23%

Petroleum, 40%

Coal, 23%

Nuclear, 8%

Biomass, 47%

Hydroelectric, 45%

Geothermal, 5%

Solar, 1%Wind, 2%

Total = 100.3 quads Renewables = 6.1 quads

Renewables, 6%

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• Fossil fuels will be a dominant energy carrier in the 21st century.

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Projected Growth in Bio-Transportation FuelsP

erce

nt o

f Tra

nspo

rtatio

n Fu

els U. S. DOE, 2005

• Biomass may become an increasingly important energy carrier.

0

5

10

15

20

1/1/1900 1/2/1900 1/3/1900 1/4/1900

Year2005 2010 2020 2030

US DOE, 2005

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Projected Growth in Bio-Transportation Fuels

0 10 20 30 40 50 60 70 80

1

2

3

4

5

6

7

8

9

10

Carbon Emissions - gC/km

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0Total Energy Use - MJ/km

NiMH Battery Electric

FC (PEM) Hybrid - hydrogen

FC (PEM) Hybrid - methanol

FC (PEM) Hybrid - gasoline

SI Hybrid - CNG

Ad. CI Hybrid - diesel fuel

Ad. SI Hybrid - gasoline

Advanced CI - diesel fuel

Advanced SI - gasoline

Current SI -gasoline

MIT Energy Lab, 2000

Automotive Engine/Fuel Performance

MIT Energy Lab, 2000

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Mitigation of GHG emissions from transportation sources will require implementation of a variety of strategies:

• improvements in overall efficiency of vehicle/fuelsystems, such as hybrid and new high-efficiencydiesel engines

• use of synthetic or renewable fuels to replace orsupplement petroleum-based fuels or as performance-improving additives

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• An attractive class of synthetic fuels is oxygenated liquidfuels that may be synthesized from a variety of feedstocks.

• Oxygenated fuels are especially attractive for use inadvanced diesel engines and diesel-hybrids because ofthe inherently high thermal efficiencies of these engines.

• In addition, these fuels offer significant potential forreduction in particulate emissions from diesel engines.

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• How well an oxygenated fuel works to reduce sootdepends on its molecular structure.

Westbrook and Pitz, 2005

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Project Goals

• Explore the impact of oxygenated fuel structure oncombustion and emissions performance under dieselcombustion conditions

- determine fuel structures that will minimize pollutantemissions (especially soot) and provide suitableignition properties

- identify processing strategies to produce syntheticoxygenated hydrocarbons from various feedstockson a refinery scale

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Research Tasks• Task 1a: Experimentally investigate the combustion and

emissions characteristics of oxygenated fuels usingtwo high-pressure combustion facilities – shock tubeand flow reactor.

• Task 1b: Develop and validate detailed chemical kineticsmodels for these fuels to provide insight into themechanisms by which fuel structure impactscombustion behavior.

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Research Tasks• Task 2: Use advanced CFD models to examine effects of

fuel structure and in-cylinder processes on soot andNOx formation and ignition in diesel engineenvironments.

• Task 3: Identify functionalities most suitable for clean-burning diesel fuels.

• Task 4: Explore strategies for production of candidateoxygenated fuels on a large-scale basis from avariety of feedstocks.

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GCEP

Compound C H O N MW MW/O Alcohols 1 Methanol 1 4 1 0 32 32 2 Ethanol 2 6 1 0 46 46 3 Butanol 4 10 1 0 74 74 4 Hexanol 6 14 1 0 102 102 5 Octanol 8 18 1 0 130 130

Ethers 6 Dimethyl ether 2 6 1 0 46 46 7 Diethyl ether 4 10 1 0 74 74 8 Dimethoxymethane 3 8 2 0 76 38 9 2,2-Dimethoxy propane 5 12 2 0 104 52

10 Ethyleneglycol dimethyl ether 4 10 2 0 90 45

11 Diethyleneglycol methyl ether 5 12 3 0 120 40

12 Triehtyleneglycol methyl ether 7 16 4 0 164 41

Esters 13 Methyl acteate 3 6 2 0 74 37 14 Methyl propanoate 4 8 2 0 88 44 15 Ethyl propanoate 5 10 2 0 102 51 16 Methyl butanoate 5 10 2 0 102 51 17 Ethyl butanoate 6 12 2 0 116 58 18 Diethyl carbonoate 5 10 3 0 118 39.7 19 Methyl soyate

Compound C H O N MW MW/O Ketones 20 Acetone 3 6 1 0 58 58 21 3-Pentanone 5 10 1 0 86 86 22 2-Pentanone 5 10 1 0 86 86 23 Acetophenone 8 8 1 0 120 120 Aldehydes 24 Butanal 4 8 1 0 72 72 25 Pentanal 5 10 1 0 86 86 26 Hexanal 6 12 1 0 100 100 Misc. 27 2-Ethylhexyl nitrate 8 17 3 1 161 53.7 28 Di-t-butyl peroxide 8 18 2 0 146 73 29 2-Nitropentane 5 11 2 1 103 51.5 30 Amyl nitrate 5 11 3 1 119 39. 7 31 Amyl nitrite 5 11 2 1 103 51.5

Screening Structures for Effectiveness in Soot Suppression

Task 1

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Screening Structures for Effectiveness in Soot Suppression

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

0 5 10 15 20 25

Wt% Oxygen

Methanol

Ethanol

Butanol

Hexanol

EthyleneglycolDME

Methyl acetate

Diethyl ether

Dimethoxymethane

Dimethoxypropane

Methyl propanoate

Ethyl propanoate

Methyl butanoate

Ethyl butanoate

Diethyl carbonoate

Acetone

2 Pentanone

3-Pentanone

Ethyl acetate

DiethyleneglycolDME

Butanal

Pentanal

Hexanal

Data from Kirby and Boehman, Penn State Fuels Lab

Smok

e H

eigh

t –m

m*

Neat fuel

* ASTM D1322

Task 1

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Screening Structures for Effectiveness in Soot Suppression

• Effectiveness of soot suppressing additives depends on themass of oxygen in the fuel blend and on molecular structure

Task 1

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Screening Structures for Effectiveness in Soot Suppression

• Effectiveness of soot suppressing additives depends on themass of oxygen in the fuel blend and on molecular structure

• The smoke point tests indicate that:

- for a given oxygen functionality the effectivenessincreases with chain length

Task 1

21

GCEP

Screening Structures for Effectiveness in Soot Suppression

• Effectiveness of soot suppressing additives depends on themass of oxygen in the fuel blend and on molecular structure

• The smoke point tests indicate that:

- for a given oxygen functionality the effectivenessincreases with chain length

- effectiveness scales as aldehydes >> ketones > ethers esters > alcohols

≈

Task 1

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Ignition Behavior of DME and DME-Heptane mixtures

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0.64 0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82

100

1000

φ = 0.5

φ = 1

Stanford data (current study) Model, Curran, et al (2000)

Stanford data (current study) Model, Curran, et al (2000)

Stanford data (current study) Model, Curran, et al (2000)

τ ign [µs

]

1000/T [1/K]

1% DME in Ar/O2

P = 1.8 atmScaled as P-0.66

φ = 2

0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82 0.84100

1000

1% DME Data 1% DME Model

.75% DME/.25% Heptane Data .75% DME/.25% Heptane Model

.5% DME/.5% Heptane Data .5% DME/.5% Heptane Model

.25% DME/.75% Heptane Data .25% DME/.75% Heptane Model

τ ign [µs

]

1000/T [1/K]

1% Total fuel in Ar/O2

φ = 1P scaled to 1.5 atm (P-0.68)

Task 1

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Sooting Characteristics of Heptane and DME-Heptane Mixtures

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Soot Induction Times

Task 1

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Sooting Characteristics of Heptane and DME-Heptane Mixtures

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Fraction of Fuel Carbon Converted to Soot

Task 1

TSD

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General Objectives

• Required computational capabilities

– LES and RANS

– Immersed boundary method for complex geometry

– Surrogate fuels

– Advanced combustion models

– Advanced soot models

• Assess effect of fuel structure on emissions in Diesel engine combustion and examine fuel optimization

GCEP

CFD Modeling of Diesel Engine Combustion

Task 2

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Strategy for New Code

StrategyBased on existing LES codes

– Required accuracy and numerical methods– Multi-phase models in place

• Strategy for moving and complex geometry– Moving meshes for moving piston– Immersed boundary for valves and possibly

piston bowl

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CFD Modeling of Diesel Engine Combustion

Task 2

TSD

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Present Work

Current Work

• Interfacing IB implementation with STL files– STereoLithography:

Industry standard for geometry representation

• Finalize compressible solver• More test cases: Realistic

engine simulations

GCEPCFD Modeling of Diesel Engine Combustion

Task 2

TSD

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Present WorkGCEP

CFD Modeling of Diesel Engine Combustion

Task 2

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Posters

• Effect of Pressure on the Oxidation of Hydrocarbon Fuels underFlameless Oxidation Conditions – Walters and Bowman: #9

• Shock Tube Studies of Soot Formation in Heptane-Air andHeptane-DME-Air Mixtures - Hong, Davidson and Hanson: #2

• Ignition Delay Times of DME/O2/Ar and DME/Heptane/O2/Ar Mixtures –Cook, Davidson and Hanson: #1

• Advanced Modeling and Optimization of Diesel Engines – Shashank,Wang, Iyengar and Pitsch: #10

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GCEP

"The use of vegetable oils for engine fuels may seem insignificant today. But such oils may become in the course of time as

important as the petroleum and coal tar products of the present time"

Rudolph Diesel, 1912

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Projected Growth in Bio-Transportation FuelsGeneric RTL Synfuels Process

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Estimated Recoverable Coal Reserves(1,000 billion tons)

GCEP

India10%

Australia9%

South Africa5%

Poland2%

ROW9% USA

27%

FSU25%

China13%

BP Global 2005