Low Temperature Automotive Diesel Combustion

Light-Duty Combustion Experiments

Paul Miles (Presenter)

Sandia National Laboratories

Light-Duty Combustion Modeling

Rolf Reitz

University of Wisconsin

May 10, 2011

Program Manager: Gurpreet Singh, DOE EERE-OVT M OF

E YD PAR

T ENT NE ERG

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AUNI

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MR C

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ST S

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TA

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2011 DOE Office of Vehicle Technologies

Program Review

2011 DOE Office of Vehicle Technologies

Program Review

This presentation does not contain any proprietary, confidential, or otherwise restricted information Project ID# ACE002

OverviewOverview

Timeline:

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Barriers addressed:

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Technical targets addressed:

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Budget:

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Relevance of Sandia’s major technical

accomplishments (May 2010 – March 2011)

Relevance of Sandia’s major technical

accomplishments (May 2010 – March 2011)

1 Varied ignition quality and volatility independently in an orthogonal matrix to

examine the impact of these fuel properties on LTC CO and UHC emissions Barriers/Targets: Improved fundamental understanding of the role of fuel properties on enabling LTC combustion; fuel property parameter sweeps for modeling validation & sensitivity studies; Tier 2, bin 2 emissions target; 40% diesel fuel economy improvement (links to UW 1)

2 Assessed accuracy and implementation of RNG turbulence models Barriers/Targets: Improved modeling of in-cylinder processes (UW 2)

3 Examined asymmetries and mean flow structure in the induction flow via Par­

ticle Image Velocimetry Barriers/Targets: Improved understanding and improved modeling of in-cylinder processes (UW 3)

4 Investigated wall-wetting by post-injections for PM trap regeneration for vari­

ous injection timings and diesel/biodiesel fuel blends Barriers/Targets: Improved understanding of in-cylinder processes (penetration, spray disruption by exhaust flows); efficiency penalty of PM trap regeneration; 30 $/kW cost target

5 Consolidated measurements and simulations to provide a phenomenological

picture of light-load LTC combustion Barriers/Targets: Improved understanding and improved modeling of in-cylinder processes; Tier 2, bin 2 emissions target; 40% diesel fuel economy improvement (links to past UW work)

Relevance of UW’s major technical

accomplishments (May 2010 – March 2011)

Relevance of UW’s major technical

accomplishments (May 2010 – March 2011)

1 Examined sources of discrepancy in UHC and CO distributions between model

and experiment & identified spray/entrainment model as a dominant source Barriers/Targets: Improved understanding and improved modeling of in-cylinder processes; Tier 2, bin 2 emissions target; 40% diesel fuel economy improvement (links to SNL 1)

2 Evaluated variable density gas jets and engine flows with RNG turbulence clo­

sure; derived alternative model dependent on the ‘dimensionality’ of the strain Barriers/Targets: Improved modeling of in-cylinder processes (SNL 2)

3 Examined intake flow modeling with detailed port, valve, and combustion

chamber mesh; examine impact of flow-field non-uniformities on UHC and CO Barriers/Targets: Improved understanding and improved modeling of in-cylinder processes; Tier 2, bin 2 emissions target; 40% diesel fuel economy improvement (SNL 3)

4 Examined light-duty RCCI combustion; upgraded engine fuel system(s) Barriers/Targets: Improved understanding and improved modeling of in-cylinder processes; Tier 2, bin 2 emissions target; 40% diesel fuel economy improvements

5 Improved soot model based on PAH kinetics; compared results to conventional,

PCCI, and RCCI combustion in light- and heavy-duty engines Barriers/Targets: Improved understanding and improved modeling of in-cylinder processes; Tier 2, bin 2 emissions target; 40% diesel fuel economy improvement; cost-effective emission control

Technical/Programmatic ApproachTechnical/Programmatic Approach

GM 1.9 l head/cylinder set

GM-CRL, UW-DERC funded

DOE funded

DOE & GM funded

DOE & GM-CRL funded

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Our approach coordinates and leverages the strengths of several institutions and

funding sources:

Programmatic:

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Accomplishments: In-cylinder sources of UHC/COAccomplishments: In-cylinder sources of UHC/CO

Task:

Investigate the impact of fuel ignition quality and volatility on the UHC/CO emissions and combustion efficiency of PCI LTC through measurements made in an orthogonal fuel property matrix

Volatility (T90 [oC])

99 281 341

Ce

tan

e N

um

be

r

PRF CN38 HMN CN38

PRF CN47 HMN CN47

Diesel

PRF CN56 (n-heptane)

HMN CN56

FACE CN53

FACE CN38

FACE CN47

31138

47

56

53

Results:

Cetane number is the dominant fuel property impacting UHC & CO

Large volatilty changes are needed to impact engine emissions

Images show that despite greater piston films and crevice UHC, low volatility fuels provide lower bulk gas UHC & CO

High ignition quality like­wise lowers bulk gas UHC & CO

Variation in bulk gas CO as cetane number varies with fixed volatility (UHC is similar)

10

15

20

25

30

35

40

45

-32 -28 -24 -20 -16 -12 -8 -4

CO

[g/k

W-h

r]

SOI [CA]

0

2

4

6

8

10

12

-32 -28 -24 -20 -16 -12 -8 -4

HMN CN56 HMN CN47 HMN CN38

UH

C [g

/kW

-hr]

SOI [CA]

HMN CN56 HMN CN47 HMN CN38

0

2

4

6

8

10

-32 -28 -24 -20 -16 -12 -8 -4

Diesel PRF CN47 HMN CN47 FACE CN47

UH

C [g

/kW

-hr]

SOI [CA]

15

20

25

30

35

40

45

-32 -28 -24 -20 -16 -12 -8 -4

CO

[g/k

W-h

r]

SOI [CA]

Diesel PRF CN47 HMN CN47 FACE CN47

0

2000

4000

6000

8000

10000

[ppm]

−20

−15

−10

−5

0 [mm]

−20

−15

−10

−5

0 [mm]

0 10 20 30 40 r (mm)

0 10 20 30 40 r (mm)

CN56 CN47

Accomplishments: In-cylinder sources of UHC/COAccomplishments: In-cylinder sources of UHC/CO

Task:

Identify the source of the discrepancy between the experiments and regarding the dominant in-cylinder source of UHC and CO emissions

Results:

Previous work demonstrated that:

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But the most promising improvement was associated with

the new gas jet spray modeling:

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CO

C2 (partially­burned)

0

0.5

1

0

0.5

1

white isotherm = 1200 K

green isotherm = 1500 K

Mole Fraction

5.0 x 10-3

0.0UHC

CO Mole

Fraction

0.00

0.01

Experiment Simulation

3FTVMUT�IBWF�UIF� HSFBUFTU�TFOTJUJWJUZ�UP� 3 s and 1inj

'VUVSF�XPSL�XJMM�GPDVT� on model tuning to predict a range of 3 s � 1inj �BOE�Enozzle

Accomplishments: Turbulence model assessmentAccomplishments: Turbulence model assessment

Background:

Standard k-ε turbulence modeling cannot predict both compression and expansion with a single set of constants

Task:

Investigate the performance of the (variable constant) RNG k-ε model

Results:

The RNG closure severely over­estimates k and l, due to the underestimation of ε

The penetration of variable density gas jets is under­predicted for the same reasons

The flow and turbulence

modeling underpins the

simulation of the mixing

and combustion pro­

cesses

Turbulent

kinetic

energy

k [

Sp2

] ε

[S p2

/s]

Dissipation

Experiment

Experiment

Experiment

RNG

RNG

RNG

Std. k-ε model

Std. k-ε model

-60 -40 -20 0 20 40 60 Crank Angle

-0.01

0

0.01

0.02

0.03

0.04

0.05 0

0.5

1

1.5

l [m

m] Length

scale

0

2

4

6

8

10

12

14

-60 -40 -20 0 20 40 60 Crank Angle

Std. k-ε model

Time [ms]

He

tip p

enet

ratio

n [m

m]

0 0

10

20

30

40

50

60

1 2 3 4 5 6

Experiment

RNG

Std. k-ε model

Accomplishments: Turbulence model short-

comings: causes and redress

Accomplishments: Turbulence model short­

comings: causes and redress

Redress:

An alternative compressible RNG closure based on the ‘dimension­ality’ of the flow field has been developed and is being tested

As implemented, C3 is computed as strain rate (Sij) dependent – it is not evaluated in the rapid distortion limit

KIVA RNG k-ε coding:

if(diverg(i4).gt.0.0) then ce3=0.41333+0.06899*reta*retaeq

else ce3=0.41333-0.06899*reta*retaeq

endif

)1(3 6

1 )(

1 3 2– 4 1

3

δ μ

ν ν

−+

⋅∇ +

+ =

C

dt dCC

U} ( ) 3

2 0

1 1

ηβηηη

+ −

)) ijS ijS2=η k ε

In this case, the RNG-specific terms are:

In this implementation, the model behaves considerably better (similar to k-ε), though it has no physical/mathematical basis

Future work will focus on more thor­ough model testing against engine measurements and DNS calculations

Difference between the characteristic strain rate and the characteristic rate associated with pure spherical distortion, S11 = S22 = S33 = ( )/3

} ( ) ⎥ ⎦

⎤ ⎢ ⎣

⎡ ⋅∇−

+ −

U

⋅∇ U

3 62

1 1

3 0

2

ijij SSC

ηβεηηημ( )U⋅∇+ =εη,3CR

Time [ms]

He

tip p

enet

ratio

n [m

m]

0 0

10

20

30

40

50

60

1 2 3 4 5 6

Experiment

RNG

Generalized RNG

AAccccomplishments:omplishments:

IInn--ccylinder floylinder flow charw characactterizaerizationtion

Task:

Characterize in-cylinder flow structure to:

i) Validate induction stroke calculations

ii) Clarify flow structure for closed-cycle simulations

iii)

Evaluate asymmetry of the pre-combustion flow(need for 360° grid)

Method: Horizontal Plane PIV with distortion correction

Results: 50° b TDC h = 3 mm h = 10 mm h = 18 mm

Exhaust Exhaust

Intake Intake

30 m/s Black circle identifies center of swirl structure

15 (4.5) Numbers in parenthesis repre­h = 3 mm (2.2)h = 10 mm10 sent swirl ratio, circles representh = 18 mm

1-σ deviation (3.5)5

Laser Sheet

(2.2)

Sw

irl Center Tilt

Swirl center tilt (and pre­cessional motion) is:

0

y [m

m]

(3.5)-5Raw (4.5)

Image - Insensitive to swirl ratio -10 (4.5)

- Present in individual cycles(2.2) -15

(3.5) - Less variable at high Rs -20Piston Mirror Corrected -15 -10 -5 0 5 10 15 20

Image x [mm]

AAccccomplishments:omplishments:

IInn--ccylinder floylinder flow charw characactterizaerizationtion

Results:

14

Measured Data Bessel Fit

12

10

8

6 α = 2.3 Rs = 2.1

Mea

n Ta

ngen

tial V

elo

city

, Vθ

[m/s

]

4

ω r R α ⎛ c b sVθ (r, t) = ⋅ J1 α2 4 J2 ( )α ⎝⎜⎜

0

r ⎞⎟⎟rb ⎠

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Radius (from center of swirl structure) [m]

The average value of α(” swipro”) over all swirl ratios and measurement locations is

α

= 2.2 Comparison with previous LDV data suggests this value is independent of port geometry

Comparison with

model results:

A full 3-d mesh of the GM engine has been created

z r

Comparison with horizontal and vertical plane PIV measurements, for various turbu­lence models, is in progress (Note the ab­sence of a major clearance volume vortex)

? Model

Ref. Vector

(10 m/s)

Experiment

Supe

rcha

rgin

g ai

r coo

ler

Accomplishments:

Post-injection wall wetting with biofuel blends

Accomplishments:

Post-injection wall wetting with biofuel blends

Task:

Examine the impact of biodiesel content on wall-wetting when post-injections for DPF regeneration are employed

i) Neat D2 versus biofuel blends ii) Impact of injection timing iii) Potential for jet disruption by

exhaust flows

Method:

Results:

Air

cool

er

SCR or LNTDOC CDPF

Tin, CDPF ≈ 600°C

Tin, DOC ≈ 300°C

TExh ≈ 380°C

TEVO ≈ 525°C

UHC ≈ 6000–8000 ppm

Simulate in cylinder conditions typical of highway-like PDF regeneration (5 bar, 1500 rpm) assuming a close coupled DOC

Cylinder

wall

Cert. D2 PME20 SME100

With early post-injec­

tion, none of the fuels

wet the cylinder wall

(consistent with liner

friction studies) SOI=44.5° aTDC, m=5.1 mg, P=20 bar, T=1100 K

All of the fuels impact

the cylinder wall with

conventional timing,

even with small post­

injection quantities

Wetting is more

severe and persistent

with biofuel blends

SOI=78.5° aTDC, m=3.3 mg, P=7 bar, T=900 K

Injection during the

exhaust blowdown

period fails to signifi­

cantly disrupt jet

penetration SOI=133.5° aTDC, m=3.3 mg, P=3.5 bar, T=750 K

2.5° aSOI

(47° aTDC)

3.5° aSOI

0.9° aEOI

(82° aTDC)

6.5° aSOI

3.9° aEOI

(85° aTDC)

Swirl

3.5° aSOI

0.9° aEOI

(137° aTDC)

AAccccomplishments: Daomplishments: Data cta consolidaonsolidation andtion and

phenomenological picphenomenological picturture of light-e of light-dutduty Ly LTTCC

Heavy-duty LTC (Musculus & Pickett) 0 10 20 30 40 50 0 10 20 30 40 50

1.0° ASI

12.0° 3.0° ASI ASI

4.0° ASI

5.0° 14.0° ASI ASI

6.0° ASI

20.0° 7.0° ASI ASI

8.0° ASI 40.0°

ASI

10.0° ASI

Light-duty, early-injection LTC 0 10 20 30 40 mm 0 10 20 30 40 mm

-22° 0° 1° ASI 23° ASI Peak

2nd-stage AHRR

15° -20°

3° ASI Peak

rate of injection

30°

-19° 4° ASI

-17.5° 50°5.5° ASI

-12.5° 10.5° ASI Peak

1st-stage AHRR

-5° 18° ASI Intermediate Ignition

(CO, UHC)

Second-Stage Ignition of Intermediate Stoichiometry or Diffusion Flame (OH)

Second-Stage Ignition of (H2CO, H2O2, CO, UHC) fuel-rich mixtures

Liquid Fuel First-Stage Ignition

Pre-ignition Vapor Fuel Head of Entrainment Soot or Soot Precursors (PAH) Wave

CollaborationsCollaborations

17

Within Vehicle Technologies program:

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4RVJTI WPMVNF

0.01

0.02

0.03

0.04

0.05

0.06

0 0.5 1 1.5 2 2.5

k DNS ε DNS

Modeled k, optimal C3Modeled ε, optimal c3

Time [s]

k, ε

[con

sist

ent u

nits

]

0.6 < η < 2.3

SummarySummary

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t� 5FDIOJDBM�BDDPNQMJTINFOUT�UIJT�SFQPSUJOH�QFSJPE�JODMVEF� - Understanding of the impact of fuel properties on LTC UHC/CO in-cylinder emission sources - Improved modeling of LTC combustion and UHC/CO emissions - Identification of problems with compressible RNG turbulence model and implementations - New compressible RNG closure model dependent on mean flow ‘dimensionality’ - Measurement of swirl flow structure and asymmetries; full 360° grid and initial simulations - Imaging study of post-injections spray wall impingement for neat diesel and biofuels - Consolidation of data and development of phenomenological picture of light-duty LTC to

complement heavy-duty work

t� 'VUVSF�XPSL�XJMM�JODMVEF�� - Continuation of UHC/CO imaging and modeling, with emphasis on capturing the influence of

engine design and operating parameter dependence; measurement of pre-combustion φ-dist. - Continued efforts to improve compressible RANS flow modeling – which underpins the modeling - Continuation of flow (and horizontal plane UHC distributions), with an emphasis on

understanding asymmetries and the necessity of modeling them