響と計測技術および生成・排出特性」

(1)

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

著者千田二郎

雑誌名第8回技術セミナー「エンジン排気微粒子の健康影

響と計測技術および生成・排出特性」

ページ 1‑36

発行年 2006‑03‑13

権利同志社大学エネルギー変換研究センター

URL http://doi.org/10.14988/re.2017.0000015756

(2)

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

Doshisha University

Emission reduction approaches More regulation on particle matter emission

from diesel engine is gradually conducted Recently…

Regulation on particulate matter emissions from diesel vehicles

-Aftertreatment technologies DPF

-Combustion Method HCCI

MK Combustion

Low temp. rich combustion -Fuel modification

Oxgenated fuels Biodiesel fuels -Improving atomization

and turbulent mixing

High pressure fuel injection small orifice nozzle

Recent Research Attempts against the Emission Regulation

JAPAN EU USA

0 0.05 0.10 0.15 0.20 0.25

1998 2000 2002 2004 2006 2008 2010

P M [g /k W h ]

(3)

Doshisha University–Energy Conversion Research Center & Spray and Combustion Science Laboratory – (D. B. Kittelson, J. Aerosol Sci, Vol.29, No.5/6, pp.575-588, 1998)

Typical particle diameter distribution

Mass weighting Number weighting Nuclei

mode

Nanoparticles Dp<50nm

Ultra fine particles Dp<100nm

Fine particles D_p<2.5mm

PM10 D_p<10mm

Accumulation mode

Coarse mode 0.001 0.010 0.100 1.000 10.000

Diameter [ m]

N o rm a liz e d c o n c e n tr a ti o n d C /C to ta l/ d lo g D

p

Nanoparticles (d

_p

<50nm) ex.) Soot, SOF

→

Serious health damage Lung cancer

breathing problem

due to low mass concentration

→Nanoparticles is unregulated

High number concentration

Investigate soot formation characteristic

focused on soot volume fraction and particle diameter in diesel spray flame

Investigate effects of various parameters on particulate characteristics

Objectives

Back ground of this study

Soot Formation Processes in Detailed Model

R e a c ti o n t im e ( a f e w m ill is e c o n d s )

Gas phase reaction

(2) Primary particle formation

(1) Initial PAH formation

Nucleation PAH growth Surface growth

Coagulation Agglomeration

(3) Soot particle formation

Fuel O

₂

H

₂

H

₂

O CO

₂

Soot

Model

(4)

Conceptual Model of Diesel Jet Flame

(Dec, SAE Paper 970873, 1997) Temporal sequence of auto-ignition &

premixed combustion phase

Chemiluminescence emission region

Auto-ignition

PAH & soot formation

Diffusion flame

Flesh oxygen entrainment

Lift-off length Rich fuel / air mixture

_st

=20~30%

Products of rich combustion CO, UHC & particulates

NO

_x

CO

₂

& H

₂

O

Soot concentration High Low

0 10 20

Scale

Quasi-steady combustion phase

Fuel droplets

Fuel vapor OH forming

region

Air entrainment

Soot precursor (PAHs)

Soot growth region Large diameter Low number density

T=2000-2100K

=0.7-1.0

Young soot Small diameter High number density

Soot oxidation region T=2200-2400K High concentration

of OH Head vortex

Conceptual model of diesel combustion

by Aizawa/Kosaka/Kamimoto in TIT

(5)

Doshisha University–Energy Conversion Research Center & Spray and Combustion Science Laboratory – fuel: n-heptane, T_amb=900[K], _amb=16.2[kg/m³], X_o2=17%, P_inj=70[MPa]

D is ta n c e f ro m n o z z le [ m m ]

20 40

80 60

100 20 40

80 60

100 (167) (14) (4) (4) (6)

1.4ms 2.0ms

TASI= 2.5ms 3.0ms 4.0ms

d _p f _v

Low High

Soot volume fraction: f

_v

Particle diameter: d

_p

[nm] 0 100

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 0

1000 1400 1800 2200 2600 3000 Temperature [K]

E q u iv a le n c e r a ti o

1%

10% 5% 15%

20%

25%

Soot

5000ppm NO

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

(6)

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 Modeling of 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 Oxygenate DGM: [CH

₃

OCH

₂

CH

₂

]

₂

O

Operating Condition

all

= 1.0 EGR ratio: 30 vol%

B o s c h s m o k e [ % ]

80

60

40

20 0 32 34 36 38 40

Oxygen content in fuel [% by mass]

Using highly oxygenated fuel 1. Stoichiometric

2. Non-sooting

combustion can be realized!!

(7)

First aromatic ring formation

C

₂

H

₃

+C

₂

H

₂

[C

₄

H

₅

]

^#

C

₄

H

₄

_-H ^+H n-C

₄

H

₃

2

C

₂

H

₂

n-C

₄

H

₅

+ C

₂

H

₂

+H -H

₂

+H High temperature route

Low temperature route

C

₃

H

₃

+C

₃

H

₃

c-C

₆

H

₆

C C H

+C

₂

H

₂

-H

+H -H

₂

+C

₂

H

₂

-H +H

C C H

-H

+C

₂

H

₂

HACA reaction sequence Ring-ring condensation

+

+H -H

₂

+C

₂

H

₂

-H +H

Combination of resonantly stabilized radicals

+ -H

₂

+ -H

₂

Reaction Model of Soot Formation

Step.1 Gas Phase Chemistry

n-Heptane fuel DME fuel DMM fuel MeOH fuel

MB fuel

Fuel chemistry

HACA reaction sequence Ring-ring condensation Combination of resonantly

stabilized radicals

PAH growth chemistry

Particle inception Particle

coagulation Surface growth

and oxidation

PAH condensation H

H

₂

C

₂

H

₂

O

₂

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

(8)

Expression of soot yield, particle diameter and soot volume fraction

ini

M

1

SY m

Soot yield・・・・・・・・・・・・

1/3

c 1

soot

soot 0

6m M

d M

Particle diameter・・・・・・

3

v soot 0

F d M

Soot volume fraction・・・ 6

soot

M

0

N

Particle number・・・・・・・

10 7.5 5 2.5

0 1

0.75 0.5 0.25 0

1400 1600 1800 2000 2200

Shock tube experiments (Kellerer’s)

1.2ms 0.9ms 0.5ms 0.3ms 0.1ms

Calculations 1.2ms

0.9ms 0.5ms

0.3ms 0.1ms

F

v

[p p m ] F

v

[p p m ]

Temperature [K]

Model Validation I: Temperature Dependence of Soot Formation

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

(9)

Model Validation II: Pressure Dependence of F _v , d _soot , N _soot

0 1 2 3 4 5 6 7

Pressure [MPa]

4 3 2 1 0 d

soot

[n m ] Shock tube experiments (Kellerer’s)

Exp. (F

_v

x 1/6) Model

8 6 4 2

21

x 1 0 N

soot 3

s m /c ] le ic rt a [p 0 2.0 1.5 1.0 0.5 0 F

v

[p p m ]

Exp. (d

_soot

x 1/8) Model

Exp. (N

_soot

x 10) Model

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

5 4

3 2

1 0

E q u iv a le n c e r a ti o

1000 1500 2000 2500

Temperature [K]

Particle diameter

Calculations 5nm

40nm

Model Validation III: Sooting Limit on Equivalence Ratio - Temperature Diagram

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

Calculations 9x10

¹²

/cm

³

1x10

¹²

/cm

³

Particle number density

1%

5%

10%

15%

20%

Calculations

Soot yield

Experiments

= Wang , et al.

(10)

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

(a) n-Heptane (C

₇

H

₁₆

) reactions 0.4

0.3 0.2

0 0.5

50 0 100 150

N

₂

H

₂

CO CH

₄

C

₂

C

₃

Aldehydes

Time [ s]

0.1 O

₂

n-C

₇

H

₁₆

H

₂

O CO

₂

H

₂

O

₂

Aromatics C

₄

1000 1500 2000

In te g ra te d m o la r fr a c ti o n o f g a s -p h a s e s p e c ie s T e m p . [K ]

(b) DME (CH

₃

OCH

₃

) reaction 1000

1500 2000

0.6 0.5 0.4 0.3 0.2 0.1 0

Time [ s]

T e m p . [K ]

N

₂

H

₂

CO

CH

₄

Aldehydes

O

₂

H

₂

O CO

₂

H

₂

O

₂

CH

₃

OCH

₃

C

₂

0 20 40 60 80 100 In te g ra te d m o la r fr a c ti o n o f g a s -p h a s e s p e c ie 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

(11)

Oxygenated Fuels Examined

Oxygenates (Code name)

Oxygen content [% by mass]

Molecular equation

Methanol

(MeOH) CH

₃

OH 50

Dimethyl ether

(DME) 34.8

Dimethoxy methane

(DMM) 42.1

Methyl butanoate 31.4 (MB)

CH

₃

OCH

₂

OCH

₃

CH

₃

OCH

₃

CH

₃

(CH

₂

)

₂

(CO)OCH

₃

Effect of Fuel Type on PAH Formation

(p=10 MPa, [C]=4.21x10 ¹⁹ ~1.26x10 ²⁰ atoms/cm ³ , reaction time: t= 3ms, isometric pyrolysis reaction)

50 40 30 20 10 0

1000 1500 2000 2500

Initial temperature [K]

P A H y ie ld [ C

PAH

/C

fuel

% ] ^n-Heptane MB

DME DMM MeOH

(a) PAH yield (1000 ~ 2400 K)

50 40 30 20 10 0

0 20 40 60

Oxygen content [% by mass]

P Y

max

[% ]

10 30 50

n-Heptane

MB

DME

DMM MeOH

(b) PAH yield (bell peak temp.)

(12)

＊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

7 6 5 4 3 2 1

1300 1700 2100 2300 0 Temperature [K]

E q u iv a le n c e r a ti o

(a) Benzene reactions

3x10

¹³

/cm

³

3x10

¹²

/cm

³

7 6 5 4 3 2 1

1300 1700 2100 2300 0 Temperature [K]

E q u iv a le n c e r a ti o

(b) n-Heptane reactions

3x10

¹³

/cm

³

3x10

¹²

/cm

³

7 6 5 4 3 2 1

1300 1700 2100 2300 0 Temperature [K]

E q u iv a le n c e r a ti o

(c) DME reactions

9x10

¹²

/cm

³

3x10

¹²

/cm

³

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

(13)

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

5nm 40nm 80nm

100nm 120nm 7

6 5 4 3 2 1

1300 1700 2100 2300 0 Temperature [K]

E q u iv a le n c e r a ti o

(a) Benzene reactions

5nm 40nm 80nm 7

6 5 4 3 2 1

1300 1700 2100 2300 0 Temperature [K]

E q u iv a le n c e r a ti o

(b) n-Heptane reactions

5nm 40nm 7

6 5 4 3 2 1

1300 1700 2100 2300 0 Temperature [K]

E q u iv a le n c e r a ti o

(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

0 1300 1700 2100 2500

E q u iv a le n c e r a ti o C /O a to m ic r a tio

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. limit Low temp. limit

Critical equivalence ratio Critical equivalence ratio

H ig h te m

p . li m it H ig h

te m p . li m

it

(14)

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．

turb i kin

i i

i

f

Y Y

,

*

Y

_i

: current concentration Y

_i^*

: equilibrium concentration

kin,i

: kinetic timescale

turb

: turbulent timescale〜k/

f : delay coefficient

i kin

i i i kin

Y Y

,

* ,

Production rate of species i

Kinetic controlled production rate of species i

dt Y dt

Y Y

_i _i _i

Y

_i

: current concentration

Y

_i^‘

: concentration after CHEMKIN cal.

dt : numerical time-step

Y dt Y Y

i i i i kin

* ,

＊Assumptions

*

0

, , f

fuel kin i kin

Y

ⁱ ⁱ ^f ^f ⁱ

f f kin

Y Y Y Y Y

dt Y Y

) / (

*

New species at the current time-step

f dt Y Y dt Y

Y Y

turb kin

i f f i

n i n i

) /

1

(

i turb kin

kin

Y

f

Turbulence chemistry interaction model

(Kong et al. SAE paper 2001-01-1026)

(15)

Temporal change of distribution of flame temperature

(fuel: n-heptane, T_amb=900[K], _amb=16.2[kg/m³], p_inj=70[MPa], t_inj=2.65[ms])

120 30 60 90 0

D is ta n c e f ro m n o z z le o ri fi c e [ m m ]

120 30 60 90 0

D is ta n c e f ro m n o z z le o ri fi c e [ m m ]

0.2ms

TASI = 0.6ms 0.7ms 0.8ms 1.0ms 1.2ms 1.4ms

1.5ms

TASI = 2.0ms 2.5ms 3.0ms 4.0ms 5.0ms 6.0ms

Temperature [K] 900 2800

temperature

Temporal change of equivalence ratio in jet

[-] 0 120 fai

30 60 90 0

D is ta n c e f ro m n o z z le o ri fi c e [ m m ]

120 30 60 90 0

D is ta n c e f ro m n o z z le o ri fi c e [ m m ]

0.2ms

TASI = 0.6ms 0.7ms 0.8ms 1.0ms 1.2ms 1.4ms

1.5ms

TASI = 2.0ms 2.5ms 3.0ms 4.0ms 5.0ms 6.0ms

1 2 3 4 5 6 7

(16)

naphthalene masss fraction [ppm] 0 400

Distribution of naphthalene mass fraction and soot volume fraction

soot volume fraction

20 0

soot volume fraction [ppm]

120 30 60 90 0

D is ta n c e f ro m n o z z le o ri fi c e [ m m ]

120 30 60 90 0

D is ta n c e f ro m n o z z le o ri fi c e [ m m ]

0.7ms

TASI = 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 4.0ms

0.7ms

TASI = 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 4.0ms

naphthalene mass fraction

Soot volume fraction and soot particle diameter in a combusting diesel jet

Soot measurement

Laser-Induced Incandescence

Soot volume fraction : f _v

Time-resolved LII

Soot particle diameter : d _p

Soot Measurement Scheme

(17)

Soot particle temperature increases rapidly by high energy laser

Soot

Radiation

Laser sheet

Laser-Induced Incandescence (LII)

In addition, LII signal intensity f

_v

Soot incandescence (LII signal) irradiates

→Visualization of soot distribution

Principle of LII

Advantage of LII for soot diagnostics Fundamental properties of LII

F

_v∝N_p･d_p³

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

(18)

2 4 4

4 ( )

rad flame

q a T T

( )

8

_m

abs

Q aE

2 0 2 5

0

2 4

[exp( ) 1]

LII p

em em

S c h N a

hc kT

3 154 / em 3

LII p p p p v

S N d N d f

At maximum temperature of soot particle (by Melton ^# ) LII signal (S _LII )

(

^#

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 50

Time after laser incident [ns]

10^-3 10^-1

10^-2 10^-0

LII signal [Normalized] Increasing diameter 20, 40, 60, 80 100, 150, 300nm

Time-Resolved LII

(19)

Laser-Induced Incandescence (LII)法の原理

CCD camera with 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 an that at 2200K

Wavelength [nm]

200 600 800 1000

In te n s it y

10

⁰

400 10

²

10

⁶

10

⁸

10

⁴

S/N

Wavelength [nm]

200 600 800 1000

In te n s it y

10

⁰

400 10

²

10

⁶

10

⁸

10

⁴

Wavelength [nm]

200 600 800 1000

In te n s it y

10

⁰

400 10

²

10

⁶

10

⁸

10

⁴

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 ∝

N _p d _p ^3+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

(20)

ＬＩＩシグナル強度に及ぼすレーザ強度の影響

Laser fluence [J/cm

²

]

0.4 0.6 0.8 1.2 1.6

0 0.2 0

300 400 600 500 700

200 100

L II s ig n a l [a .u .]

1.4 1.0

Plateau region

Premixed burner

（

=2.3, HAB=12mm）

Laser fluence [J/cm

²

]

0.4 0.6 0.8 1.2 1.6

0 0.2 0

300 400 600 500 700

200 100

L II s ig n a l [a .u .]

1.4 1.0

Plateau region

Premixed burner

（

=2.3, HAB=12mm）

Laser fluence [J/cm

²

]

0.4 0.6 0.8 1.2 1.6

0 0.2 0

300 400 600 500 700

200 100

L II s ig n a l [a .u .]

1.4 1.0

Plateau region

Premixed burner

（

=2.3, HAB=12mm）

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 50

Time after laser incident [ns]

10^-3 10^-1

10^-2 10^-0

LII signal [Normalized] Increasing diameter 20, 40, 60, 80 100, 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 ^0.0⁰ ²⁰ ⁴⁰ ⁶⁰ ⁸⁰ ¹⁰⁰

0.1 0.2 0.3 0.4

Particle diameter [nm]

LII signal ratio

(21)

change of internal 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

4 ( ) 4 0

3

v

abs t rad s s

s

H dM dT

Q a q a T T q a C

W dt dt

2 2

4 4

s v

2

v

dM da RT

a a

dt dt W

Power balance of a laser-heated soot particle

K

_abs

Time after laser incident [ns]

0 10 20 30 40 50

2000 4500 4000 3500 3000

T e m p e ra tu re [ K ] 2500

0 100 80 60 40 20

D ia m e te r [ n m ]

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

(22)

Time after laser incident [ns]

0 10 20 30 40 50

10 ⁰

10 ^-1

10 ^-2

10 ^-3

N o rm a liz e d L II s ig n a l in te n s it y

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

P _amb =4.1MPa, Laser fluence=0.92J/cm ² , T _flame =2200K increasing diameter

20, 40, 60, 80, 100,150, 300nm 10 ⁰

Time after laser incident [ns]

N o rm a liz e d L II s ig n a l

10 20 30 40 50

10 ^-1

10 ^-2

10 ^-3 0

Laser pulse

(23)

LII signal decay for various particle sizes

P _amb =4.1MPa, Laser fluence=0.92J/cm ² , T _flame =2200K increasing diameter

20, 40, 60, 80, 100,150, 300nm 10 ⁰

Time after laser incident [ns]

N o rm a liz e d L II s ig n a l

10 20 30 40 50

10 ^-1

10 ^-2

10 ^-3

promptLII

0 Laser pulse

LII signal decay for various particle sizes

P _amb =4.1MPa, Laser fluence=0.92J/cm ² , T _flame =2200K increasing diameter

20, 40, 60, 80, 100,150, 300nm 10 ⁰

Time after laser incident [ns]

N o rm a liz e d L II s ig n a l

10 0 20 30 40 50

10 ^-1

10 ^-2

10 ^-3

delayLII

Laser pulse

(24)

Particle diameter [nm]

25 75 100 150

0 L II s ig n a l ra ti o r

50 0.5

0.2

0.1 0 0.3 0.4

125

P_amb=4.1MPa, Laser fluence=0.67J/cm², T_flame=2200K first second

S r S

LII signal ratio of first and second gate versus particle diameter

Time-Resolved LII

によるすす粒子径の決定法

promptLII (raw image) delayLII (raw image)

1) delayLII promptLII

Diameter distribution

シグナル比を算出

2) From signal ratio to diameter

0 20 40 60 80 100

0.0 0.1 0.2 0.3 0.4

Particle diameter [nm]

LII signal ratio

(25)

increasing ambient pressure 0.1, 1.0, 2.0, 3.0,

4.0, 5.0MPa

10 0 20 30 40 50

Time after laser incident [ns]

10

⁰

L II s ig n a l [n o rm a li z e d ]

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

C

₂

H

₂

O

₂

N

₂

ECD-U2

Amp Timing control unit

Amp

P

P.C Injector

Vacuum pump Spark

plug

Stirrer

Pressure transducer

Mixing tank

Pressure gauge Stirrer

Pressure pick up Spark plug

Intake Exhaust

Pressure gauge

(26)

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/m ³ ]

Lower calorific value [MJ/kg]

Boiling point [K]

Kinematic viscosity [mm ² /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．

(27)

Experimental condition

Ambient gas temperature T _amb [K]

Injection pressure drop P _inj [MPa]

Ambient gas density _amb [kg/m ³ ] Ambient oxygen concentration X _O2 [%]

Set injection duration t _inj [ms]

Injection quantity Q _inj [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)

d _p f _v

f _v and d _p distribution ( P _inj =70MPa)

d

_p

[nm]

0 20 40 60 80 100<

f

_v

low high

D is ta n c e f ro m n o z z le [ m m ] 40

50 60 70

D is ta n c e f ro m n o z z le [ m m ] 40

50

60 TASI=* 70

(28)

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

f _v

f _v and d _p distribution ( P _inj =70MPa)

D is ta n c e f ro m n o z z le [ m m ] 40

50 60 70

D is ta n c e f ro m n o z z le [ m m ] 40

50 60 TASI=* 70

d

_p

[nm]

0 20 40 60 80 100<

f

_v

low high

0.92(2.30ms) d _p

f _v

1.12(2.80ms) 1.2(3.00ms) f _v and d _p distribution ( P _inj =70MPa)

D is ta n c e f ro m n o z z le [ m m ] 40

50 60 70

D is ta n c e f ro m n o z z le [ m m ] 40

50 60 TASI=* 70

d

_p

[nm]

0 20 40 60 80 100<

f

_v

low high

(29)

燃料噴射圧力の影響

(上段： p

_inj

=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

Distance from nozzle [mm] 40

50 60 70

TASI=*

* TASI*= t

_inj

/ t

_inj

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：X

_o2

=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

50 60 70

TASI=*

* TASI*= t

_inj

/ t

_inj

dp[nm]

0 20 40 60 80 100<

dp[nm]

0 20 40 60 80 100<

(30)

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 T

_amb

[K]

Fuel

Injection pressure drop P

_inj

[MPa]

Ambient gas density

_amb

[kg/m

³

] Ambient oxygen concentration X

_O2

[%]

Injection duration t

_inj

[ms]

Injection quantity Q

_inj

[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

(31)

Doshisha University–Energy Conversion Research Center & Spray and Combustion Science Laboratory – fuel: n-heptane, T_amb=900[K], _amb=16.2[kg/m³], X_o2=21%, P_inj=70[MPa]

D is ta n c e f ro m n o z z le [ m m ]

20 40

80 60

100 20 40

80 60

100 (1071) (54) (21) (9) (5)

1.0ms 1.2ms

TASI= 1.3ms 1.5ms 1.8ms

d _p f _v

Low High

Soot volume fraction: f

_v

Particle diameter: d

_p

[nm] 0 100

Rate of heat release [kJ/s]

200 800

400

2 8 12

Time after start of injection [ms]

0 0

10

4 6

400 1000

800

0

Cumulative heat release [J]

Injection duration

600

200 600

200 800

400

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

600

200 600

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

D is ta n c e f ro m n o z z le [ m m ]

20 40

80 60

100 20

40 80 60

100 (3) (3) (4) (4) (14)

2.0ms 2.5ms

TASI= 3.0ms 3.5ms 4.0ms

d _p f _v

fuel: n-heptane, T_amb=900[K], _amb=16.2[kg/m³], X_o2=21%, P_inj=70[MPa]

Low High

Soot volume fraction: f

_v

Particle diameter: d

_p

[nm] 0 100

Distribution of soot volume fraction and soot particle

diameter in diesel jet flame obtained by Time-resolved LII

(32)

Doshisha University–Energy Conversion Research Center & Spray and Combustion Science Laboratory – fuel: n-heptane,_amb=16.2[kg/m³], X_o2=21%, P_inj=70[MPa]

D is ta n c e f ro m n o z z le [ 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 d

_p

f

_v

Low High

Soot volume fraction: f

_v

Particle diameter: d

_p

[nm] 0 100

T

_amb

=800[K]

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

0.5ms 1.0ms 2.0ms 3.5ms T

_amb

=1200[K]

d

_p

f

_v

300 1500

600

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

1200

200 600 900

300 1500

600

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

1200

200 600 900

T

_amb

=800K

100 400

200

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

300

200 600

100 400

200

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

300

200 600

T

_amb

=1200K Distribution of soot volume fraction and soot particle

diameter in diesel jet flame obtained by Time-resolved LII

fuel: n-heptane, T_amb=900[K], _amb=16.2[kg/m³], X_o2=13%, P_inj=70[MPa]

D is ta n c e f ro m n o z z le [ m m ]

20 40

80 60

100 20

40 80 60

100 (152) (135) (34) (23) (10)

2.0ms 2.5ms

TASI= 3.0ms 3.5ms 4.5ms

d _p f _v

Low High

Soot volume fraction: f

_v

Particle diameter: d

_p

[nm] 0 100

100 400

200

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

300

200 600

100 400

200

2 8 12

0 0

10

4 6

400 1000

800

0

Injection duration

300

200 600

X

_o2

=13%

Distribution of soot volume fraction and soot particle

diameter in diesel jet flame obtained by Time-resolved LII

(33)

A re a -a v e ra g e d f

v

0 200 400 600 800

0 20 40 60 80 100

0 1.0 2.0 3.0 4.0 A re a -a v e ra g e d d

p

[n m ]

Time after start of injection [TASI

^*

] 1200K 900K

800K

A re a -a v e ra g e d f

v

0 200 400 600 800

0 20 40 60 80 100

A re a -a v e ra g e d d

p

[n m ]

0 1.0 2.0 3.0 4.0

Time after start of injection [TASI

^*

] 7.0 5.0 6.0 17% 21%

13%

Integrated LII intensity and characteristic particle 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

(34)

Flame temperature [K]

2000

1800 1900 2100 2200 2300 2400 P _amb =4.1MPa, Laser fluence=0.67J/cm ² 0.2

0 -0.2

-0.4 0.4

d p / d p [- ]

10nm 50nm 80nm d _p @2200K

Effect of flame temperature on calculated diameter

0.50 0.60 0.70 0.80

Laser fluence [J/cm ² ] 2.5

2.0 1.5 1.0 0.5 0 -0.5 d p / d p [- ]

P _amb =4.1MPa, T _flame =2200K 10nm 50nm 80nm d _p @0.67J/cm ²

Effect of laser fluence on calculated diameter

(35)

TASI=0.8ms, _g =1.45, D _g =7 0

1.0 0.8

P a rt ic le d is tr ib u ti o n [ N o rm a liz e d ]

0.4 0.6

0.2 Particle diameter [nm]

0 20 40 60 80

Experiment Log-normal Log-normal fitting of soot particle

-0.6 0.4 0.2

d p /D T IR E

-0.2 0

-0.4

D ₁₀ D ₂₀ D ₃₀ D ₃₂

D ₄₃ D ₆₃

g =1.6

D

_g

=10, D

_TIRE

=19.6nm D

_g

=15, D

_TIRE

=29.2nm D

_g

=20, D

_TIRE

=39.1nm D

_g

=25, D

_TIRE

=48.4nm

Relative error of D _mn to D _TIRE

(36)

響と計測技術および生成・排出特性」

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

著者 千田 二郎

雑誌名 第8回技術セミナー「エンジン排気微粒子の健康影

響と計測技術および生成・排出特性」

ページ 1‑36

発行年 2006‑03‑13

権利 同志社大学エネルギー変換研究センター

URL http://doi.org/10.14988/re.2017.0000015756

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

2006.3.13

Emission reduction approaches More regulation on particle matter emission

from diesel engine is gradually conducted Recently…

-Aftertreatment technologies DPF

-Combustion Method HCCI

MK Combustion

Low temp. rich combustion -Fuel modification

Oxgenated fuels Biodiesel fuels -Improving atomization

and turbulent mixing

High pressure fuel injection small orifice nozzle

Recent Research Attempts against the Emission Regulation

JAPAN EU USA

0 0.05 0.10 0.15 0.20 0.25

1998 2000 2002 2004 2006 2008 2010

P M [g /k W h ]

Typical particle diameter distribution

Mass weighting Number weighting Nuclei

mode

Accumulation mode

Coarse mode 0.001 0.010 0.100 1.000 10.000

Diameter [ m]

N o rm a liz e d c o n c e n tr a ti o n d C /C to ta l/ d lo g D

Nanoparticles (d

<50nm) ex.) Soot, SOF

Serious health damage Lung cancer

breathing problem

due to low mass concentration

High number concentration

Investigate soot formation characteristic

focused on soot volume fraction and particle diameter in diesel spray flame

Investigate effects of various parameters on particulate characteristics

Objectives

Back ground of this study

Soot Formation Processes in Detailed Model

R e a c ti o n t im e ( a f e w m ill is e c o n d s )

Gas phase reaction

(2) Primary particle formation

(1) Initial PAH formation

Nucleation PAH growth Surface growth

Coagulation Agglomeration

(3) Soot particle formation

Fuel O

H

H

O CO

Soot

Model

Conceptual Model of Diesel Jet Flame

(Dec, SAE Paper 970873, 1997) Temporal sequence of auto-ignition &

premixed combustion phase

Chemiluminescence emission region

Auto-ignition

PAH & soot formation

Diffusion flame

Flesh oxygen entrainment

Lift-off length Rich fuel / air mixture

=20~30%

Products of rich combustion CO, UHC & particulates

NO

CO

& H

O

Soot concentration High Low

0 10 20

Scale

Quasi-steady combustion phase

Fuel droplets

Fuel vapor OH forming

region

著者千田二郎

雑誌名第8回技術セミナー「エンジン排気微粒子の健康影

権利同志社大学エネルギー変換研究センター

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

d _p f _v

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