The Effect of Dimethyl Ether Addition on Sooting Limits in ... · Sooting Limits in Counterflow...

Clean Combustion Research Center, King Abdullah University of Science & Technology (KAUST)

The Effect of Dimethyl Ether Addition on

Sooting Limits in Counterflow Diffusion

Flames at Elevated Pressures

Zepeng Li, Peng Liu, Hafiz M. F. Amin, Yu Wang, Suk Ho Chung, William L. Roberts

Clean Combustion Research Center, (CCRC)

King Abdullah University of Science and Technology (KAUST)

Saudi Arabia

Clean Combustion Research Center, King Abdullah University of Science & Technology (KAUST)2

CONTENT

Introduction

Methodology

Results and Discussion

Conclusions


Motivation and background

Soot: carbonaceous particles

resulting from incomplete

combustion of hydrocarbon

fuels.

Incomplete Combustion: Efficiency

Deposition : Burner Lifetime / Performance

Health: Carcinogenic and Mutagenic

Climate: Global Warming & Regional

precipitation

Dimethyl Ether

(DME)

AdvantagesHigh oxygen content & the

absence of C–C bonds: smokeless

combustion, low formation and high

oxidation rates of particulates.

High cetane number

Low boiling point

Disadvantages Low energy density

High requirements on sealing

materials


Sooting tendency

Quantitative sooting metrics were pronounced to evaluate sooting

tendency among a wide range of hydrocarbon fuels, e.g., TSI, YSI.

[1] Yang Y, Boehman AL, Santoro RJ. Combust Flame

2007;149:191–205.

[2] McEnally CS, Pfefferle LD. Combust Flame 2007;148:210–22.

Threshold soot index (TSI) [1] Yield soot index (YSI) [2]


CONTENT

Introduction

Methodology


Conclusions


Experimental setup

Schematics of experimental apparatus: Light scattering setup (a), and atmospheric

counterflow burner (b)

Light scattering technique + Counterflow diffusion flames


Numerical Simulation

Flame temperatures and species concentrations of

experimental flames were computed using Chemkin Pro. A

soot model is not included in the simulation due to the

negligible impact of soot on flame temperature at the sooting

limit.

• Module: Opposed-flow Flame package

• Reaction kinetic model: KAUST-Aramco PAH Mech 1

(KAM1)

[1] Park, Sungwoo, et al. "Compositional effects on PAH and soot formation in counterflow diffusion flames of gasoline

surrogate fuels." Combustion and Flame 178 (2017): 46-60.


CONTENT

Introduction

Methodology


Conclusions


How to determine sooting limits

2.1 2.4 2.7 3.00

2

4

6

Xo=0.16

Xo=0.17

Sca

tter

ing

in

ten

sity

(A

. U

.)

Distance from fuel nozzle [mm]

P=1 atm

Xf=1

Xo,cr

=0.17

Xo=0.18

The sooting limit map defined as the critical oxygen mole fraction

(Xo) related to the fuel mole fraction (Xf) at soot inception point is

detailed discussed in [1,2].

[1] Y. Wang, S.H. Chung. Combust. Flame 161.5 (2014): 1224-1234.

[2] P.H. Joo, Y. Wang, A. Raj, S.H. Chung, Proc. Combust. Inst. 34 (2013) 1803–1809.

Notation

β: DME mixing ratio

β≡[𝐶

2𝐻6𝑂]

𝐶2𝐻6𝑂 +[𝐶

2𝐻4]


Repeatability

[1] Y. Wang, S.H. Chung. Combust. Flame 161.5 (2014): 1224-1234.

[2] P.H. Joo, Y. Wang, A. Raj, S.H. Chung, Proc. Combust. Inst. 34 (2013) 1803–1809.

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

SFO SF

F F

O O

SFO

Non-sooting region

Fuel mole fraction, XF

Ox

yg

en m

ole

fra

ctio

n, X

O

Ref. [8]

Setup 1

Setup 2

Ethylene Flame

1470

1644

1819

1993

2168

2342

2516

2691

2865

Max.

Fla

me

Tem

per

atu

re (

K)

Sooting region

SF

OF

Flame zone

Soot zone

Oxidizer

Fuel mixture


0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

=0

SFO


Oxyg

en m

ole

fra

ctio

n, X

O

Sooting region

Non-sooting region

SF

(a)

SFO

SF

=0.5

∆Xo

1. Sooting Limit Map

Highest sooting propensity:

0~ 10% DME addition

∆Xf 1. The addition of DME

reduces sooting tendency

among β=0.1-0.5.

2. ∆Xf > ∆Xo : small thermal

effect in SF flames, while

high thermal effect in SFO

flames.

3. Sooting limit curves are

overlapped when β<0.1.


2. Highest sooting tendency

0 2 4 6 8 10

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Norm

aliz

ed m

ax. sc

atte

ring

inte

nsi

ty (

A. U

.)

DME mixing ratio (%)

=5.7%

R2=0.787

Maximum scattering intensity as a function of DME mixing ratios (β) with 95%

confidence band.

Highest sooting

propensity: 5.7%

DME addition

Critical DME mixing

ratio = 5.7%


0.0 0.1 0.2 0.3 0.4 0.50.16

0.20

0.24

0.28

0.4 0.6 0.8 1.0

Quadratic term

coefficient

Fuel mole fraction, xf

Xf=1

Xf=0.85

Xf=0.7

Xf=0.55

Xf=0.4

DME mixing ratio,

Cri

tica

l o

xy

gen

mo

le f

ract

ion

, X

o,c

r

0.05

3. Dilution effect

When the fuel

(or carbon flow)

is diluted, the

dependence of

dilution on

sooting

tendencies

increases

Critical oxygen mole fraction as a function of DME mixing ratios (β)


0.0

0.2

0.4

0.6

0.8

1.0

P (atm)

1

2

3.5

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0


Ox

yg

en

mo

le f

racti

on

, X

O

0.0 0.2 0.4 0.6 0.8 1.0

4. Pressure effect

As pressure

increases,

sooting tendency

increases

Sooting limit maps with respect to DME mixing ratios (β) at P=1, 2, 3.5 atm


0.00 0.05 0.10 0.15 0.20 0.250.0

0.2

0.4

0.6

0.8

1.0

P=1 atm

cr=0.057

R2=0.787

P (atm) 1

2

3.5

P=3.5 atm

cr=0.144

R2=0.739

P=2 atm

cr=0.106

R2=0.806

No

rmali

zed

max

. sc

att

erin

g i

nte

nsi

ty (

A. U

.)

DME mixing ratio,

4. Pressure effect

The range of β in

increasing soot

propensity expands

with pressure.

The effort to

reduce soot by

doping DME may

not be effective at

high pressures.

Sooting propensity with DME mixing ratio at several pressures


5. Kinetic analysis

0.0 0.1 0.2 0.3 0.4 0.50.0

1.5

3.0

4.5

6.0

7.5M

ole

fra

ctio

n o

f b

enze

ne

(1E

-4)

DME (or FDME) mixing ratio

P=1atm, Thermal contribution

P=1atm, Chemical contribution

P=3atm, Thermal contribution

P=3atm, Chemical contribution

Thermal and chemical contributions to benzene production at P = 1, 3 atm.


CONTENT

Introduction

Methodology


Conclusions


Conclusions

The sooting limits (Xf and XO) are significantly sensitive to pressure, and the sooting

tendency increases at higher pressure. The range of β in increasing soot propensity

with DME addition expands with pressure, thus the effort to reduce soot by doping DME

may not be effective at high pressures.

When the fuel (or carbon flow) is diluted, the dependence of dilution on sooting

tendencies increases. That is, as Xf decreases, the increase of Xo,cr with respect to DME

mixing ratio becomes more sensitive, meaning that the effect of DME addition on sooting

tendency increases as the fuel is diluted.

The behaviors of the DME effect on sooting limits in SF flame and SFO flame are

slightly different. Sooting tendency is more sensitive in SFO flames than in SF flames

due to the thermal effect.

Kinetical analysis indicate that soot formation with DME addition is dominantly

determined by the synergistic chemical effect, which is likely realized by the pathway

of DME→CH3(H)→C2H2(C2H3&C3H3)→C6H6→soot.


Acknowledgements

This work is supported by Clean Combustion

Research Center (CCRC), King Abdullah University

of Science and Technology (KAUST), Saudi Arabia.

Clean Combustion Research Center, King Abdullah University of Science & Technology (KAUST)

THANK YOU

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