ディーゼル燃焼場におけるすす粒子生成過程 …†低温酸化・高温酸化・熱分解～7環PAH 生成ﾓﾃﾞﾙ・n-ヘプタン反応モデル—Curranらのモデル

Doshisha University – Energy Conversion Research Center & Spray and Combustion Science Laboratory –

ディーゼル燃焼場におけるすす粒子生成過程と Time-Resolved LII による

火炎中すす粒子計測

学術フロンティア「次世代ゼロエミッション・エネルギー変換システム」技術セミナー「エンジン排気微粒子の健康影響と計測技術および生成・排出過程」

１．背景＆研究目的２．化学反応動力学によるすす生成過程の解析３．ＬＩＩによる燃焼火炎場のすす粒子測定

同志社大学大学院工学研究科千田二郎2006.3.13


Emission reduction approachesMore regulation on particle matter emission from diesel engine is gradually conducted

Recently…

Regulation on particulate matter emissions from diesel vehicles

-Aftertreatment technologiesDPF

-Combustion MethodHCCIMK CombustionLow temp. rich combustion

-Fuel modificationOxgenated fuels Biodiesel fuels

-Improving atomizationand turbulent mixing

High pressure fuel injectionsmall orifice nozzle

Recent Research Attempts against the Emission Regulation

JAPAN

EU

USA

0

0.05

0.10

0.15

0.20

0.25

1998 20102000 2002 2004 2006 2008

PM [

g/kW

h]


(D. B. Kittelson, J. Aerosol Sci, Vol.29, No.5/6, pp.575-588, 1998)

Typical particle diameter distribution

Mass weighting Number weighting

Nucleimode

NanoparticlesDp<50nm

Ultra fine particlesDp<100nm

Fine particlesDp<2.5mm

PM10Dp<10mm

Accumulationmode

Coarsemode

0.001 0.010 1.0000.100 10.000Diameter [ m]

Nor

mal

ized

con

cent

ratio

n dC

/Cto

tal/d

logD

p

Nanoparticles (dp<50nm)ex.) Soot, SOF

→ Serious health damageLung cancerbreathing problem

due to low mass concentration→Nanoparticles is unregulated

High number concentration

Investigate soot formation characteristic focused on soot volume fraction and particle diameterin diesel spray flame Investigate effects of various parameters on particulate characteristics

Objectives

Back ground of this study


Soot Formation Processes in Detailed Model

Rea

ctio

n tim

e (a

few

milli

seco

nds)

Gas phase reaction

(2) Primary particle formation

(1) Initial PAH formation

Nucleation

PAH growth

Surface growthCoagulation

Agglomeration

(3) Soot particle formation

Fuel O2

H2

H2OCO2

SootModel


Conceptual Model of Diesel Jet Flame(Dec, SAE Paper 970873, 1997)

Temporal sequence of auto-ignition & premixed combustion phase

Chemiluminescenceemission region

Auto-ignition

PAH & soot formation

Diffusion flame

Flesh oxygen entrainment

Lift-off lengthRich fuel / air

mixture st=20~30%Products of rich combustion

CO, UHC & particulates

NOx

CO2 & H2O

Soot concentrationHighLow

0 10 20

Scale

Quasi-steady combustion phase


Fuel droplets

Fuel vapor

OH formingregion

Air entrainment

Soot precursor(PAHs)

Soot growth regionLarge diameter

Low number densityT=2000-2100K

=0.7-1.0

Young sootSmall diameter

High number density

Soot oxidation regionT=2200-2400K

High concentrationof OH

Head vortex

Conceptual model of diesel combustionby Aizawa/Kosaka/Kamimoto in TIT


fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], Xo2=17%, Pinj=70[MPa]D

ista

nce

from

noz

zle

[mm

]20

40

80

60

10020

40

80

60

100

(167) (14) (4) (4) (6)

1.4ms 2.0msTASI= 2.5ms 3.0ms 4.0ms

dp

fv

Low HighSoot volume fraction: fvParticle diameter: dp [nm] 1000

Distribution of soot volume fraction and soot particle diameter in diesel jet flame obtained by Time-resolved LII


7

6

5

4

3

2

1

01000 1400 1800 2200 2600 3000

Temperature [K]

Equi

vale

nce

ratio

1%5%10%15%

20%

25%

Soot

5000ppmNO

Low temp. rich combustion [Akihama et al., SAE Paper 2001-01-0655]

MK combustion[Kimura et al., SAE

Paper 2001-01-0200]

500ppm

HCCI

Desirable path[Kamimoto et al.,

SAE Paper 880423]

Combustion Mode in Φ－ T Map


含酸素燃料を用いた無煙ディーゼル燃焼法の化学反応論的解析

- Detailed Chemical Kinetic Modelingof Smokeless Diesel Combustion

with Oxygenated Fuels –

北村・伊藤ら

非定常噴霧燃焼場のすす粒子生成挙動の解析


Oxygen Impact on Particulate Emissions

(Miyamoto et al., Int. J. Engine Research, 1-1, pp.71-85, 2000)

Main OxygenateDGM: [CH3OCH2CH2]2O

Operating Conditionall = 1.0

EGR ratio: 30 vol%

Bosc

h sm

oke

[%]

80

60

40

20

032 34 36 38 40

Oxygen content in fuel [% by mass]

Using highly oxygenated fuel1. Stoichiometric2. Non-sootingcombustion can be realized!!


First aromatic ring formation

C2H3+C2H2 [C4H5]#

C4H4 n-C4H3+H-H2

C2H2

n-C4H5+ C2H2

+H-H2

+H

High temperature route

Low temperature route

C3H3+C3H3 c-C6H6 CC

H

+C2H2

-H+H-H2

+C2H2

-H+H

CC

H

-H+C2H2

HACA reaction sequenceRing-ring condensation

+

+H -H2

+C2H2

-H+H

Combination of resonantly stabilized radicals

+ -H2

+ -H2

Reaction Model of Soot Formation

Step.1 Gas Phase Chemistry

n-Heptane fuel

DME fuelDMM fuelMeOH fuel

MB fuel

Fuel chemistryHACA reaction sequence

Ring-ring condensation

Combination of resonantly stabilized radicals

PAH growth chemistry

Particle inception

Particle coagulation

Surface growth and oxidation

PAH condensation

HH2C2H2

O2 OH

Step.2 Soot Formation Model


Chemkin-Ⅲ SENKINコード低温酸化・高温酸化・熱分解～７環PAH生成ﾓﾃﾞﾙ

・n-ヘプタン反応モデル—Curranらのモデル・MarinovらのPAH生成ﾓﾃﾞﾙ（C4以下の低級炭化水素から

４環芳香族までの分子成長反応・CurranらのDMEﾓﾃﾞﾙ、Marinovらのｴﾀﾉｰﾙﾓﾃﾞﾙ・Fisherらのﾒﾁﾙﾌﾞﾀﾉｴｰﾄ酸化反応ﾓﾃﾞﾙ・Dalyらのｼﾞﾒﾄｷｼﾒﾀﾝ酸化反応ﾓﾃﾞﾙ

すす粒子生成ﾓﾃﾞﾙはFrenklachらのﾓｰﾒﾝﾄ法による

粒子生成ﾓﾃﾞﾙ・HACAﾒｶﾆｽﾞﾑ-芳香族環への水素引抜き-ｱｾﾁﾚﾝ付加反応・FrenklachらのPAH生成ﾓﾃﾞﾙ

Gas Phase Chemistry – 素反応モデル


Expression of soot yield, particle diameter and soot volume fraction

ini

1MSY mSoot yield・・・・・・・・・・・・

1/3

c 1soot

soot 0

M6md MParticle diameter・・・・・・

3soot

v 0dF M6Soot volume fraction・・・

0soot MNParticle number・・・・・・・


10

7.5

5

2.5

0 10.75

0.50.25

01400 1600 1800 2000 2200

Shock tube experiments (Kellerer’s)

1.2ms0.9ms0.5ms0.3ms0.1ms

Calculations 1.2ms

0.9ms0.5ms0.3ms

0.1ms

Fv [ppm

]F v

[ppm

]

Temperature [K]

Model Validation I: Temperature Dependence of Soot Formation

(fuel: benzene, =5, p=3 MPa, reaction time: t=0.1~1.2 ms)


Model Validation II: Pressure Dependence of Fv, dsoot, Nsoot

0 1 2 3 4 5 6 7Pressure [MPa]

43210

dsoot [nm

]Shock tube experiments (Kellerer’s)

Exp. (Fv x 1/6)Model

86420

Nso

otx

1012

[par

ticle

s/cm

3 ]

2.01.51.00.5

0

F v[p

pm]

Exp. (dsoot x 1/8)Model

Exp. (Nsoot x 10)Model

(fuel: toluene, =5, T=1600 K, p=3 MPa, reaction time: t=1.5 ms)


5

4

3

2

1

0

Equi

vale

nce

ratio

1000 1500 2000 2500Temperature [K]

Particle diameter

Calculations5nm

40nm

Model Validation III: Sooting Limit on EquivalenceRatio - Temperature Diagram

(fuel: toluene, p=0.5 MPa, reaction time: t=4.0 ms)

Calculations

9x1012/cm3

1x1012/cm3

Particle number density

1%5%

10%

15%

20%

Calculations

Soot yield

Experiments= Wang , et al.


Fuel Consumption Process in n-Heptaneand DME Reactions (T=900 K, p=8 MPa, =4)

(a) n-Heptane (C7H16) reactions

0.4

0.3

0.2

0

0.5

500 100 150

N2H2

CO

CH4

C2C3

Aldehydes

Time [ s]

0.1

O2

n-C7H16

H2O

CO2

H2O2

AromaticsC4

100015002000

Inte

grat

ed m

olar

frac

tion

of

gas-

phas

e sp

ecie

sTe

mp.

[K]

(b) DME (CH3OCH3) reaction

100015002000

0.6

0.5

0.4

0.3

0.2

0.1

0

Time [ s]

Tem

p. [K

]

N2 H2

CO

CH4

AldehydesO2

H2O

CO2

H2O2

CH3OCH3 C2

0 20 60 10040 80

Inte

grat

ed m

olar

frac

tion

of

gas-

phas

e sp

ecie

s


Chemical Role of Oxygenated Fuels on PAH Suppression

これまでの含酸素燃料の基礎解析によると、PAH生成およびその前駆物質であるC2,C3などの低級炭化水素生成

の抑制特性として、燃料構造が影響する。

① 主要反応生成物が重要アセチレン、エチレンなどの多環化物質は促進アルデヒド類は抑制に働く

② 酸素原子に由来するOHラジカルによる酸化分子成長反応を抑制

③ アルデヒド類はHCOラジカルを介して水素原子を生成ベンゼン前駆体のﾌﾟﾛﾊﾟﾙｷﾞﾙﾗｼﾞｶﾙの水素引き抜きベンゼン生成を抑制


Oxygenated Fuels Examined

Oxygenates(Code name)

Oxygen content[% by mass]Molecular equation

Methanol(MeOH) CH3OH 50

Dimethyl ether(DME)

34.8

Dimethoxy methane(DMM) 42.1

31.4Methyl butanoate

(MB)

CH3OCH2OCH3

CH3OCH3

CH3(CH2)2(CO)OCH3


Effect of Fuel Type on PAH Formation

(p=10 MPa, [C]=4.21x1019~1.26x1020 atoms/cm3 ,reaction time: t= 3ms, isometric pyrolysis reaction)

50

40

30

20

10

01000 1500 2000 2500

Initial temperature [K]

PAH

yie

ld [C

PA

H/C

fuel

%] n-Heptane

MBDMEDMMMeOH

(a) PAH yield (1000 ~ 2400 K)

50

40

30

20

10

00 20 40 60Oxygen content [% by mass]

PYm

ax[%

]

10 30 50

n-Heptane

MB

DME

DMM MeOH

(b) PAH yield (bell peak temp.)


＊すす生成のベル型温度依存性・低温域では熱分解による低級不飽和炭化水素の生成が遅れ、PHA抑制・高温域では分子成長反応の逆反応であるPAHの分解可能が促進

ギブス生成自由ｴﾈﾙｷﾞの観点でも、1500K以上ではPAHよりｱｾﾁﾚﾝ

などの低級不飽和炭化水素が安定

＊ベル型分布のリーン側での低温側シフト（外部酸素）・燃料の酸化反応の寄与度が増加し、初期に900K程度の低温でも酸化後の

平衡温度が1600-1700Kに達する

＊ﾃﾞｨｰｾﾞﾙ噴霧火炎内部でのすす生成の推定・低燃料噴射圧力条件：低い空気導入率

最大PAH生成温度域は1700K程度の高温噴霧外縁部の拡散火炎近傍ですす生成

・高燃料噴射圧力条件：高い空気導入率噴霧内部の当量比４程度の希薄な領域で900-1000KでPAH最大生成

噴霧中心部で活発なすす生成が生じる

Chemical Role of Molecular Oxygen and Oxygenate on PAH Suppression


Particle Number Density Map as a Function of and T for Three Fuels

765432101300 1700 2100 2300

Temperature [K]

Equi

vale

nce

ratio

(a) Benzene reactions

3x1013

/cm3

3x1012/cm3

765432101300 1700 2100 2300

Temperature [K]

Equi

vale

nce

ratio

(b) n-Heptane reactions

3x1013/cm3

3x1012/cm3

765432101300 1700 2100 2300

Temperature [K]

Equi

vale

nce

ratio

(c) DME reactions

9x1012/cm3

3x1012/cm3

(P=6 MPa, reaction time: t=2 ms)


(P=6 MPa, reaction time: t=2ms)

5nm 40nm

80nm

100nm

120nm765432101300 1700 2100 2300

Temperature [K]

Equi

vale

nce

ratio

(a) Benzene reactions

5nm40nm

80nm

765432101300 1700 2100 2300

Temperature [K]

Equi

vale

nce

ratio

(b) n-Heptane reactions

5nm

40nm

765432101300 1700 2100 2300

Temperature [K]

Equi

vale

nce

ratio

(c) DME reactions

Particle Number Density Map as a Function of φ and T for Three Fuels


Variation of Soot Formation Limits among Different Type of Fuels on -T Diagram

(defined as 1% soot yield)

Temperature [K]

7

6

5

3

4

2

1

01300 1700 2100 2500

Equi

vale

nce

ratio

C/O

atomic ratio

2.5

2.0

1.5

1.0

0.5

0.0

benz.

0.0

2.0

1.5

1.0

0.5

n-hep.

0.0

1.0

0.5

DME

n-Heptane

DME

Benzene

Low temp. limitLow temp. limit

Critical equivalence ratioCritical equivalence ratio

High temp. lim

it

High temp. lim

it


Conclusions

詳細な0次元すす反応動力学モデルにより，粒子径・粒子数を考慮したすす生成の当量比-温度マップ解析および燃料組成がすす生成特性

に及ぼす影響の検討を行ない，以下に示す知見を得た．

すす生成の当量比-温度依存性は燃料成分の影響を強く受

ける．特に，含酸素燃料では最大すす生成収率の大幅な低下やすす生成領域の大幅な縮小化が可能となる．

すす体積分率のベルピーク温度よりも低温側では，小粒径・高数密度・高PAH濃度の粒子が，逆に高温側では，大粒径・低数密度・低PAH濃度の粒子が生成される．

上記に起因して，すす排出重量の低減に加え，微小すす粒子数および未燃PAH濃度を同時に低減するには，当量比-温度マップ上におけるすす生成半島の低温側より，燃料希薄側の利用が望まれる．


turbikin

iii f

YY,

*

Yi : current concentrationYi

*: equilibrium concentrationkin,i : kinetic timescaleturb : turbulent timescale～k/

f : delay coefficient

ikin

iiikin

YY,

*

,

Production rate of species i

Kinetic controlled production rateof species i

dtY

dtYY iii

Yi : current concentrationYi

‘ : concentration after CHEMKIN cal.dt : numerical time-step

dtY

YYi

iiikin

*

,

＊Assumptions

0*

,,

f

fuelkinikin

Y iffii

ffkin

YYYYY

dtYY

)/(

)/(*

New species at the current time-step

dtf

YYYdtYY

turbkin

iffi

ni

ni

)/(1

iturbkin

kin Yf

Turbulence chemistry interaction model(Kong et al. SAE paper 2001-01-1026)


Temporal change of distribution of flame temperature(fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], pinj=70[MPa], tinj=2.65[ms])

120

30

60

90

0D

ista

nce

from

noz

zle

orifi

ce [m

m]

120

30

60

90

0

Dis

tanc

e fro

m n

ozzl

e or

ifice

[mm

]

0.2msTASI = 0.6ms 0.7ms 0.8ms 1.0ms 1.2ms 1.4ms


Temperature [K] 2800900

temperature


Temporal change of equivalence ratio in jet(fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], pinj=70[MPa], tinj=2.65[ms])

[-] 0

fai120

30

60

90

0

Dis

tanc

e fro

m n

ozzl

e or

ifice

[mm

]

120

30

60

90

0

Dis

tanc

e fro

m n

ozzl

e or

ifice

[mm

]



1 2 3 4 5 6 7


naphthalene masss fraction [ppm] 4000

Distribution of naphthalene mass fraction and soot volume fraction(fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], pinj=70[MPa], tinj=2.65[ms])

soot volume fraction

200soot volume fraction [ppm]

120

30

60

90

0D

ista

nce

from

noz

zle

orifi

ce [m

m]

120

30

60

90

0

Dis

tanc

e fro

m n

ozzl

e or

ifice

[mm

]



naphthalene mass fraction


Soot volume fraction and soot particle diameterin a combusting diesel jet

Soot measurement

Laser-Induced Incandescence

Soot volume fraction : fv

Time-resolved LII

Soot particle diameter : dp

Soot Measurement Scheme


Soot particle temperature increases rapidlyby high energy laser

Soot

Radiation

Laser sheet

Laser-Induced Incandescence (LII)

In addition, LII signal intensity vf

Soot incandescence (LII signal) irradiates→Visualization of soot distribution

Principle of LII


Advantage of LII for soot diagnostics

Fundamental properties of LII

Fv∝Np･dp3

Application of LII to diesel engine

L.A.Melton

A.C.Eckbreth

J.E.Dec

Numerical analyze of LII

LII signal intensity increase with increasing laser power

Decrease in soot diameter due to soot vaporization

LII signal intensity is proportional to soot volume fraction

Lack of scattering influence due to droplet or cylinder wall

Previous Study about Laser Induced Incandescence

Spray and Combustion Science Laboratory, DOSHISHA University


2 4 44 ( )rad flameq a T T

( )8 mabs

aEQ

220

50

2 4[exp( ) 1]LII p

em em

c hS N ahc kT

3 154 / 3emLII p p p p vS N d N d f

At maximum temperature of soot particle (by Melton#)

LII signal (SLII)

(# L. A. Melton, APPLIED OPTICS, Vol.23, No.13, pp.2201-2208, 1984)

Theoretical Equations


LII signal decay after laser incident depends on particle diameter.

LII signal ratio at two different times also depends on particle diameter.

Temporal change in LII signal decay after laser incident(LII signal ratio at two different timing, etc)

Numerical simulation

(L. A. Melton, APPLIED OPTICS, Vol.23, No.13, pp.2201-2208, 1984)as well as Melton’s method

0 10 20 30 40 50Time after laser incident [ns]

10-3

10-1

10-2

10-0

LII s

igna

l [N

orm

aliz

ed] Increasing diameter

20, 40, 60, 80100, 150, 300nm

Time-Resolved LII


Laser-Induced Incandescence (LII)法の原理

CCD camerawith I.I.(Ⅰ)

Band pass filter

Cylindrical lens(f=1000mm)

Nd:YAG Laser (532nm)

Notch filter

Cylindrical lens(f=25, 100mm)

radiation

Soot

LIIの光学系の例

レーザ光により熱せられたすす粒子からのふく射光を検出することですす濃度を測定する．レーザ光

シグナル強度∝すす体積濃度

燃料液滴や壁面等の散乱光の影響を受けにくい．


Ratio of black body radiation at 4500K anthat at 2200K

Wavelength [nm]200 1000600 800

Inte

nsity

400100

102

106

108

104

S/N


Inte

nsity

400100

102

106

108

104


Inte

nsity

400100

102

106

108

104

S/N

Ratio of black body radiation at 4500K and that at 2200K

短波長ほどS/N比が高い．

LII信号強度 ∝ Npdp3+154nm/ 長波長ほど体積濃度に比例

短波長ほどLII信号強度そのものも低い


ＬＩＩシグナル強度に及ぼすレーザ強度の影響

Laser fluence [J/cm2]0.4 1.60.8 1.20.60 0.20

300

400

600

500

700

200

100

LII s

igna

l [a.

u.]

1.41.0

Plateau region

Premixed burner （ =2.3, HAB=12mm）


300

400

600

500

700

200

100

LII s

igna

l [a.

u.]

1.41.0

Plateau region



300

400

600

500

700

200

100

LII s

igna

l [a.

u.]

1.41.0

Plateau region


ある程度のレーザ強度以上ではＬＩＩシグナル強度は飽和する．レーザシート光の強度ムラやすすによるレーザ強度の減衰の影響を受け難い．


LIIを用いたすす粒子径の計測：Time-Resolved LII (TIRE-LII)

0 10 20 30 40 50Time after laser incident [ns]

10-3

10-1

10-2

10-0

LII s

igna

l [N

orm

aliz

ed] Increasing diameter

20, 40, 60, 80100, 150, 300nm

レーザ照射後のＬＩＩシグナル強度の時間履歴は粒子直径に依存する．

異なる2時期でのＬＩＩシグナル強度比

から粒子直径を算出できる．

Laser pulse

ディーゼル燃焼場 → 高温，高圧

粒子径が既知の粒子を用いた検定実験が困難．

：単一球形粒子仮定

ＬＩＩシグナルの時間変化を数値予測 0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

Particle diameter [nm]

LII s

igna

l rat

io


change ofinternal energy

Absorption

Thermal radiation

Vaporization

Heat transfer

Energy balance equation

absorbed laser energy

heat transfer loss

heat loss soot

evaporation

internal energy change

heat loss thermal radiation

Mass conservation equation

(Stefan Will, et al, APPLIED OPTICS, Vol.37, No.24, pp.5647-5658, 1998)

2 2 3( ) 0

44 ( ) 03

vabs t rad s s

s

H dM dTQ a q a T T q a CW dt dt

2 24 42s v

v

dM da RTa adt dt W

Power balance of a laser-heated soot particle

Kabs


Time after laser incident [ns]0 10 20 30 40 50

2000

4500

4000

3500

3000

2500Tem

pera

ture

[K]

0

100

80

60

40

20

Diam

eter [nm]

すす粒子の温度および粒子径変化（初期粒径: 50nm，粒子初期温度: 2200K，レーザ強度: 0.92J/cm2）

Temperature

Diameter

Laser pulse


Time after laser incident [ns]0 10 20 30 40 50

100

10-1

10-2

10-3Nor

mal

ized

LII

sign

al in

tens

ity

LIIシグナル強度の時間履歴（初期粒径: 50nm，粒子初期温度: 2200K，雰囲気圧力：4.1MPa，レーザ強度: 0.92J/cm2）

Laser pulse

LII signal


LII signal decay for various particle sizes

Pamb=4.1MPa, Laser fluence=0.92J/cm2, Tflame=2200K

increasing diameter20, 40, 60, 80,

100,150, 300nm

100

Time after laser incident [ns]

Nor

mal

ized

LII

sign

al

10 20 30 40 50

10-1

10-2

10-3

0

Laser pulse





100,150, 300nm

100


Nor

mal

ized

LII

sign

al

10 20 30 40 50

10-1

10-2

10-3

promptLII

0

Laser pulse





100,150, 300nm

100


Nor

mal

ized

LII

sign

al

100 20 30 40 50

10-1

10-2

10-3

delayLIILaser pulse


Particle diameter [nm]25 15075 1000

LII s

igna

l rat

io r

50

0.5

0.2

0.1

0

0.3

0.4

125


first

second

SSr

LII signal ratio of first and second gate versusparticle diameter


Time-Resolved LIIによるすす粒子径の決定法

promptLII (raw image) delayLII (raw image)

1) delayLIIpromptLII

Diameter distributionシグナル比を算出

2) From signal ratioto diameter

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

Particle diameter [nm]

LII s

igna

l rat

io


increasing ambient pressure0.1, 1.0, 2.0, 3.0,

4.0, 5.0MPa

100 20 30 40 50Time after laser incident [ns]

100

LII s

igna

l [no

rmal

ized

]

10-1

10-2

10-3

大気圧場では，ＬＩＩシグナルの減衰は緩慢である．

大気圧バーナやエンジン排気中のＰＭ粒径を計測する場合はレーザ照射後数百ns後のシグナルを用いるのが一般的．

ＬＩＩシグナルの時間履歴に及ぼす雰囲気圧力の影響


Schematic diagram of experimental system

C2H2O2 N2

ECD-U2

Amp

Timing control unit

Amp

P

P.C

Injector

Vacuum pump

Sparkplug

Stirrer

Pressuretransducer

Mixingtank

Pressure gauge

Stirrer

Pressure pick up

Spark plugIntakeExhaust

Pressure gauge


CCD camera with I.I.(Ⅰ) Half mirror

Combustion vessel

Nd:YAG Laser ( =532 nm)

CCD camera with I.I.(Ⅱ)

Notch filter ( =532nm, 3nm FWHM)

Short pass filter ( =450nm)

Pin-hole

Convex lens (f=800mm)

Cylindrical lens (f=100mm)

Optical measurement system for Time-resolved LII


Property of test fuel

Fuel:N-heptane

Density at 298K [kg/m3]

Lower calorific value [MJ/kg]

Boiling point [K]

Kinematic viscosity [mm2/s]

Cetane number

Stoichiometric A/F [kg/kg]

680

372

0.584

47.8

56

15.1

軽油すす生成量が多過ぎる．レーザ光の減衰が著しく，またシート光とカメラまでのすすにより，ＬＩＩシグナルも大幅に減衰する．


Experimental condition

Ambient gas temperature Tamb [K]

Injection pressure drop Pinj [MPa]

Ambient gas density amb [kg/m3]

Ambient oxygen concentration XO2 [%]

Set injection duration tinj [ms]

Injection quantity Qinj [mg]

900

16.2

17, 21

70

2.65

18.3

Nozzle orifice diameter d [mm] 0.2

40

3.2

100

2.1


0.52(1.30ms)0.4(1.00ms) 0.44(1.10ms)

dp

fv

fv and dp distribution (Pinj=70MPa)

dp [nm]

0 20 40 60 80 100<

fv

low high

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70TASI*=


0.6(1.50ms) 0.72(1.80ms) 0.8(2.00ms)

dp

fv

fv and dp distribution (Pinj=70MPa)D

ista

nce

from

nozz

le [m

m] 40

50

60

70

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70TASI*=

dp [nm]

0 20 40 60 80 100<

fv

low high


0.92(2.30ms)

dp

fv

1.12(2.80ms) 1.2(3.00ms)

fv and dp distribution (Pinj=70MPa)

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70TASI*=

dp [nm]

0 20 40 60 80 100<

fv

low high


燃料噴射圧力の影響 (上段： pinj=40MPa，下段：100MPa)

0.4 0.44 0.52 0.6 0.72

0.8 0.92 1.12 1.2 1.32

No image

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70

TASI*=

* TASI*= tinj / tinj

dp [nm]

0 20 40 60 80 100<

dp [nm]

0 20 40 60 80 100<


雰囲気酸素濃度の影響 (上段：Xo2 =21%，下段：17%)

0.4 0.44 0.52 0.6 0.72

0.8 0.92 1.12 1.2 1.32

No image

Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70Dis

tanc

e fro

mno

zzle

[mm

] 40

50

60

70

TASI*=

* TASI*= tinj / tinj

dp [nm]

0 20 40 60 80 100<

dp [nm]

0 20 40 60 80 100<


Conclusion

すす生成開始直後は，生成領域の全域を10～20nm程度の小さな粒子が占め，拡散的燃焼期間への移行に伴い，噴霧外縁付近から大粒子へと成長する．

上流側で生成された小粒径のすすは下流に向かうに従い，凝集や表面反応により成長し，大粒子化する．

噴射圧力が増加するに従い，大粒子径のすすが生成し始める位置は下流へと遷移し，その時期は噴射時期後半へと移行する．

．

大粒子径のすすは噴霧外縁付近に多く分布し，噴霧中心軸付近は小さなすす粒子で占められる．

雰囲気酸素濃度の低下は，噴霧火炎内部で生成されるすす粒子の成長を抑制し，すすの小粒径化をもたらす．


Ambient gas temperature Tamb [K]

Fuel

Injection pressure drop Pinj [MPa]

Ambient gas density amb [kg/m3]

Ambient oxygen concentration XO2 [%]

Injection duration tinj [ms]

Injection quantity Qinj [mg]

n-Heptane

900

16.2

13

70

2.5

18.3

Nozzle orifice diameter d [mm] 0.2

800 1200

17 21

Experimental conditions


fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], Xo2=21%, Pinj=70[MPa]D

ista

nce

from

noz

zle

[mm

]20

40

80

60

10020

40

80

60

100

(1071) (54) (21) (9) (5)


dp

fv


Rat

e of

hea

t rel

ease

[kJ/

s]

200

800

400

2 8 12Time after start of injection [ms]

0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

600

200

600

Rat

e of

hea

t rel

ease

[kJ/

s]

200

800

400


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

600

200

600



Dis

tanc

e fro

m n

ozzl

e [m

m]

20

40

80

60

10020

40

80

60

100

(3) (3) (4) (4) (14)


dp

fv

fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], Xo2=21%, Pinj=70[MPa]




fuel: n-heptane, amb=16.2[kg/m3], Xo2=21%, Pinj=70[MPa]

Dis

tanc

e fro

m n

ozzl

e [m

m]

20

40

80

60

100

20

40

80

60

100

(117) (126) (38) (245)

TASI= 2.5ms 3.0ms 3.4ms 4.0ms

dp

fv


Tamb=800[K]

(10) (1) (1) (7)

0.5ms 1.0ms 2.0ms 3.5ms

Tamb=1200[K]

dp

fv

Rat

e of

hea

t rel

ease

[kJ/

s]

300

1500

600


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

1200

200

600900

Rat

e of

hea

t rel

ease

[kJ/

s]

300

1500

600


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

1200

200

600900

Tamb=800K

Rat

e of

hea

t rel

ease

[kJ/

s]100

400

200


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

300

200

600

Rat

e of

hea

t rel

ease

[kJ/

s]100

400

200


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

300

200

600

Tamb=1200K

Distribution of soot volume fraction and soot particlediameter in diesel jet flame obtained by Time-resolved LII


fuel: n-heptane, Tamb=900[K], amb=16.2[kg/m3], Xo2=13%, Pinj=70[MPa]

Dis

tanc

e fro

m n

ozzl

e [m

m]

20

40

80

60

10020

40

80

60

100

(152) (135) (34) (23) (10)


dp

fv


Rat

e of

hea

t rel

ease

[kJ/

s]

100

400

200


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

300

200

600

Rat

e of

hea

t rel

ease

[kJ/

s]

100

400

200


0

0

104 6

400

1000

800

0

Cum

ulat

ive

heat

rele

ase

[J]

Injection duration

300

200

600

Xo2=13%



Are

a-av

erag

ed f v

0

200

400

600

800

0

20

40

60

80

100

0 1.0 4.02.0 3.0

Are

a-av

erag

ed d

p[n

m]

Time after start of injection [TASI*]

1200K900K800K

Are

a-av

erag

ed f v

0

200

400

600

800

0

20

40

60

80

100

Are

a-av

erag

ed d

p[n

m]

0 1.0 4.02.0 3.0Time after start of injection [TASI*]

7.05.0 6.0

21%17%13%

Integrated LII intensity and characteristicparticle diameter


(1) 予混合的燃焼期間の終盤に生成した微小なすす粒子は

燃焼の進行とともに噴霧下流部へ拡がり，噴霧先端・外縁部で大粒子径のすすが高濃度で分布する．

(2) 雰囲気温度の低下に伴い，大幅にすす濃度が減少し，粒子径もLIIシグナルが検出される全期間において微小とな

る．

(3) 雰囲気酸素濃度が低下すると，噴霧火炎が肥大化するこ

とにより，すす生成領域が拡大する．また，雰囲気酸素濃度の低下に伴い，すす粒子の生成・成長が緩慢となることで，粒子径およびすす濃度はともに減少する．

Conclusions


Flame temperature [K]20001800 2100 2200 2300 24001900

Pamb=4.1MPa, Laser fluence=0.67J/cm2

0.2

0

-0.2

-0.4

0.4d p

/dp

[-]

10nm50nm80nm

dp@2200K

Effect of flame temperature on calculated diameter


0.50 0.60 0.70 0.80Laser fluence [J/cm2]

2.5

2.0

1.5

1.0

0.5

0

-0.5

d p/d

p[-]

Pamb=4.1MPa, Tflame=2200K

10nm50nm80nm

[email protected]/cm2

Effect of laser fluence on calculated diameter


TASI=0.8ms, g=1.45, Dg=7

0

1.0

0.8

Par

ticle

dis

tribu

tion

[Nor

mal

ized

]

0.4

0.6

0.2

Particle diameter [nm]0 20 40 60 80

ExperimentLog-normal

Log-normal fitting of soot particle


-0.6

0.4

0.2

d p/D

TIR

E

-0.2

0

-0.4

D10 D20 D30 D32

D43 D63

g=1.6

Dg=10, DTIRE=19.6nmDg=15, DTIRE=29.2nmDg=20, DTIRE=39.1nmDg=25, DTIRE=48.4nm

Relative error of Dmn to DTIRE


0 20 40 60 80 100 120 140Particle diameter [nm]

0

0.02

0.04

0.06

0.08

Pro

porti

on [-

]

0.5ms(0.21)0.8ms(0.34)1.0ms(0.43)

2.0ms(0.85)1.5ms(0.64)

2.5ms(1.06)

3.5ms(1.49)3.0ms(1.28)

TASI(TASI*)2.03, 0.452.50, 0.452.80, 0.453.40, 0.455.90, 0.456.00, 0.456.00, 0.459.21, 0.45

Temporal changes in particle size distribution forn-heptane


0.5ms(0.15)0.7ms(0.20)1.0ms(0.30)

2.3ms(0.70)1.7ms(0.50)

3.3ms(1.00)

4.0ms(1.20)3.6ms(1.10)

TASI(TASI*)1.50, 0.451.55, 0.451.80, 0.451.90, 0.452.00, 0.452.30, 0.452.40, 0.453.00, 0.45

0 20 40 60 80 100 120 140Particle diameter [nm]

0

0.02

0.04

0.06

0.08

Pro

porti

on [-

]

Temporal changes in particle size distribution for DGE


Time-Resolved LIIの問題点

検査領域中（画像ピクセル中）に粒度分布が存在する場合．見積もられる平均粒子径は概ねD32と一致するが，粒度分布によって若干異なる．

下図のように凝集体の構造が異なる場合，算出される粒子径？？？

point contact

・

loose structure

・

point contact

・ point contact

・

loose structure

・ loose structure

・

compact・

dense structure

・

compact・ compact・

dense structure

・ dense structure

・

p ppn

A A

App = primary particle surface

pA “enwrapped”surface of the agglomerate

as equivalent diameter

measured diameter=

mean primary particle diameter

measured diameter=

mean primary particle diameter

measured diameter=

“heat transfer diameter”measured diameter

=“heat transfer diameter”

より定量的な結果を得るには噴霧火炎内部の局所的な温度情報が必要とされる．

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