Dual-fuel Concept & Formulation - ETH Zürich · PDF fileTowards modelling of multiple combustion modes: Dual-fuel Concept & Formulation. ... Reduced emissions that can satisfy the

|| 09.09.2015Daniele Farrace

Verbrennungstagung - ETH Zurich - 09.09.2015 D. Farrace, Y. M. Wright and K. Boulouchos

1

Towards modelling of multiple combustion modes: Dual-fuel Concept & Formulation


▪ The main reason are the fuel costs! ▪ price decoupled from liquid fuel price

▪ increasing availability of gaseous fuels

[1]

2

Why dual-fuel combustion?

[1] M. Ott et al., 3. Rostocker Grossmotorentagung, 2014

|| 09.09.2015Daniele Farrace[2] E. J. Sixel, 3. Rostocker Grossmotorentagung, 2014

[2]



▪ Reduced emissions that can satisfy the stringent regulations of IMO Tier III ▪ reduced NOx favored by lean combustion (within Tier III w/o additional treatments)

▪ negligible sulfur oxides emissions

▪ practically no soot (PM) emissions

‣ regulation can be introduced in future

▪ theoretically lower GHG emissions

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▪ Reduced emissions that can satisfy the stringent regulations of IMO Tier III ▪ reduced NOx favored by lean combustion (within Tier III w/o additional treatments)

▪ negligible sulfur oxides emissions

▪ practically no soot (PM) emissions

‣ regulation can be introduced in future

▪ theoretically lower GHG emissions

▪ Very flexible ▪ can be operated in diesel mode when LNG is not available

4



▪ Challenges ▪ GHG emissions are lower in theory, in reality methane slip is an issue

‣ CH4 impact on atmosphere is about 100 times greater then CO2 (in 20 years time scale)

‣ 3-6 g CH4 slip per kWh during otto LNG operation [1]

▪ Effective knock control strategies are required

▪ UHC emissions due to cold walls can be significant

5


[1] T. Mundt et al., 3. Rostocker Grossmotorentagung, 2014

➡ Deep understanding of physico-chemical processes is needed in order to optimise the combustion process and meet the requirements!

▪ High-fidelity experiments can provide an insight into the combustion process

▪ CFD can support experiments by investigating not measurable data ‣ multiple combustion modes and their interaction are a challenge

‣ multiple fuels behaviour is a challenge

|| 09.09.2015Daniele Farrace 6

State-of-the-art in dual-fuel modelling▪ Knowledge of dual-fuel operation is at early stages, involved processes are not

fully understood yet…

Diesel pilotautoignition spots

flame propagation

flame kernels

▪ Autoigniting diesel spray ‣ atomization and break-up ‣ evaporation ‣ autoignition ‣ diffusion flame

▪ Regime transition ‣ premixed charge ignition ‣ flame kernels growth

▪ Turbulent premixed flame ‣ flame(s) propagation ‣ extinction

non-premixed model

premixed model

interaction


State-of-the-art in dual-fuel modelling▪ Level set approach + CTC/WM/CMC

‣ Spray ignition: CTC / Well Mixed (WM) / Conditional Moment Closure (CMC) ➡ depending on model cool flame chemistry could be considered

‣ Regime transition: flame kernel initialized when T>1200K and Rkernel>lmean

‣ Premixed flame: flame tracked by a level set method (G-equation/Weller) ➡ one-step chemistry, combustion regimes are distinguished

[1] CTC: S. Singh et al., 2005 [2] WM: Kokjohn et al., 2011 [3] CMC: S. Schlatter et al., 2011

[1][2][3]

[3]Weller 3-eqn for λCH4=1.5

!

Δt after SOI 1.7 ms 1.9 ms 2.1 ms 2.3 ms 2.5 ms

OH

dis

tribu

tion

Iso

surfa

ce b

=0.3

Weller 3-eqn for λCH4=1.5 SOI=-15°CA aTDC Percent NG= 98

[1]SOI=-15°CA aTDC


CMC double-conditioned

8

non-premixed combustion

premixed combustion

CMC premixed

tem

pera

ture

(K)

progress

CMC non-premixed

0 0.1 0.2 0.3 0.4 0.5 0.60

500

1000

1500

2000

2500

Mixture Fraction 1 [−]

Tem

pera

ture

[K]

−11.0 °CA +1.1 °CA +1.8 °CA +2.2 °CA +2.5 °CA +3.2 °CA +4.0 °CA +6.6 °CA

mixture

tem

pera

ture

mode transition

CMC non-premixed

Concept of “Multi-mode Combustion Modelling” (MC-CMC)

dual-fuel combustion


Non-premixed CMC: Work overview▪ Generic test rigs

• Aachen CVCC ✓ ignition delays, CMC physical space transport terms [1]

• ETH CVCC ✓ ignition delay/location, mech. sensitivity [2], stoch. of autoignition [3]

• Sandia CVCC ✓ ignition delays, lift-off heights [4,5], soot formation [6,7]

• ETH single stroke machine ✓ diesel pilot ignition [8]

• Marine CVCC ✓ ignition delay/location, lift-off heights [9,10]

▪ Engines • ETH Liebherr heavy-duty Diesel engine

✓ pressure [11], HRR and NOx [12], EGR [13] • Sandia heavy-duty Diesel engine

✓ HRR and soot [14], NOx [15], EGR [16], post injections [17] • ETH MTU heavy-duty Diesel engine

✓ ongoing work: NOx reduction by extreme Miller timing

Wright et al., CNF 143 (2005) [1] Wright et al., FTaC 84 (2010) [2]

Wright et al., Procs LES4ICE (2012) [3] Borghesi et al., CTM 15 (2011) [4]

Bolla et al., SAE Int. J. Engines 6 (2013) [5] Bolla et al., CST 185 (2013) [6] Bolla et al., CTM 18 (2014) [7]

Schlatter et al., Procs Dessau Conf (2011) [8] Bolla et al., Procs COMODIA (2012) [9]

Bolla et al., SAE World Congress (2014) [10]

De Paola et al., CST 180 (2008) [11] Wright et al., SAE Int. J. Engines 2 (2009) [12] Wright et al., Procs ASME ICCMSE (2010) [13]

Bolla et al., FUEL 117 (2014) [14] Farrace et al., SAE Int. J. Engines 6 (2013) [15] Farrace et al., SAE Int. J. Engines 7 (2014) [16]

Pandurangi et al., SAE Int. J. Engines 7 (2014) [17]


Non-premixed CMC: Spray Combustion Chamber (SCC)

experimentsimulation

0.25 ms 0.75 ms 1 msLiquid spray region

axial distance (mm)

Experiment Simulation

Flame evolution0.75 ms 2 ms 6 ms

d0=0.875mm 80bar 800K

d0=0.875mm 90bar 900K

[1] K. Herrmann et al., CIMAC World Congress, 2007 [2] M. Bolla et al., SAE World Congress, 2014

[1]

[1] [2]



11


premixed combustion

CMC premixed

CMC non-premixed

mode transition

CMC non-premixed

CMC premixed




IC engines

▪ Turbulent premixed combustion - regimes

12

Premixed combustion in real applications

(e)

(d)

(a)

(b)(c)

(a) (b) (c)

(d)

(e)

Simulation: Aspden et al., The Astrophysical Journal 689, 2008

Gas turbines

from Siemens (Workshop, Cambridge, 25th June 2015)


Premixed CMC: Model formulation

!u, !p, !k, !ε , !c, ′′c 2!,Zi!flow field

to CMCCMC

ρ ζ ∂Qα

∂t+ ρui ζ

∂Qα

∂xi+∂ ρui′′Yα ′′ ζ P! ζ( )⎡⎣⎢

⎤⎦⎥

P! ζ( )∂xi= !ωα ζ − !ω c ζ

∂Qα

∂ζ+ ρNc ζ

∂2Qα

∂ζ 2

initial conditions

ζ

T, Yα

10

Τ

CH4 O2

Nc ζ =εc! ⋅ f ζ( )f c( ) p c( )

0

1

∫ dc

tabulated in CHEMKIN

flow field

iterate until CMC convergence

get !ω c ζ Yα ζand

!ω c! = !ω c ζ P!

0

1

∫ ζ( )∂ζ

′′c !ω c! = ζ !ω c ζ P!

0

1

∫ ζ( )∂ζ

− !c ⋅ !ω c ζ P!0

1

∫ ζ( )∂ζ

Yα! = Yα ζ P!0

1

∫ ζ( )∂ζconvolution

required to CFD!ω c! and ′′c !ω c

!

linear interpolation or tabulated in CHEMKIN


▪ Bunsen piloted burner (from Chen et al., Combustion and Flame 107, 1996)

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flame F1 F2 F3

U0 (m/s) 65.0 50.0 30.0Re (-) 52’000 40’000 24’000

τchem (ms) 0.44 0.44 0.44

δL (mm) 0.175 0.175 0.175

τturb (ms) 0.51 0.65 1.10

lturb (mm) 2.4 2.4 2.4

F3F2F1

Premixed CMC: Bunsen flame F2 - configuration


Premixed CMC: Bunsen flame F2 - results

r/D00 0.5 1 1.5 20

0.5

1

1.5X/D0=2.5

ExpCFD

0

0.5

1

1.5X/D0=4.5

0

0.5

1

1.5X/D0=6.5

0

0.5

1

1.5X/D0=8.5

U/U

0

0

0.5

1

1.5X/D0=10.5

r/D00 0.5 1 1.5 20

5

10

15X/D0=2.5

ExpCFD

0

5

10

15X/D0=4.5

0

5

10

15X/D0=6.5

0

5

10

15X/D0=8.5

k/k 0

0

5

10

15X/D0=10.5

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▪ Cold flow (flow field validation)

X/D0=2.5X/D0=4.5X/D0=6.5X/D0=8.5X/D0=10.5

Experiment: Chen et al., Combustion and Flame 107, 1996


Premixed CMC: Bunsen flame F2- mechanism analysis

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▪ Chemical mechanism considerations in view of dual-fuel ‣ Pitsch-44 (P44) contains the relevant high temperature CH4 paths

P44 GRIr/D0

0 0.5 1 1.5 20

0.5

1

1.5X/D0=2.5

ExpCFD

0

0.5

1

1.5X/D0=4.5

0

0.5

1

1.5X/D0=6.5

0

0.5

1

1.5X/D0=8.5

U/U

00

0.5

1

1.5X/D0=10.5

r/D00 0.5 1 1.5 20

5

10

15X/D0=2.5

ExpCFD

0

5

10

15X/D0=4.5

0

5

10

15X/D0=6.5

0

5

10

15X/D0=8.5

k/k 0

0

5

10

15X/D0=10.5


Premixed CMC: Bunsen flame F2- mechanism analysis

17

▪ Chemical mechanism considerations in view of dual-fuel ‣ Pitsch-44 (P44) contains the relevant high temperature CH4 paths

P44 GRIr/D0

0 0.5 1 1.5 20

0.5

1

1.5X/D0=2.5

ExpCFD

0

0.5

1

1.5X/D0=4.5

0

0.5

1

1.5X/D0=6.5

0

0.5

1

1.5X/D0=8.5

U/U

00

0.5

1

1.5X/D0=10.5

r/D00 0.5 1 1.5 20

5

10

15X/D0=2.5

ExpCFD

0

5

10

15X/D0=4.5

0

5

10

15X/D0=6.5

0

5

10

15X/D0=8.5

k/k 0

0

5

10

15X/D0=10.5


Premixed CMC: Bunsen flame F2- results

X/D0

0 2 4 6 8 10 12

δ t (mm

)

0

5

10

15

20

25 Experiment Unstrained flamelet

X/D0

0 2 4 6 8 10 12

δ t (mm

)

0

5

10

15

20

25 Experiment Unstrained flamelet CMC based on CH4 CMC based on O2

X/D0

0 2 4 6 8 10 12

δ t (mm

)

0

5

10

15

20

25 Experiment Unstrained flamelet CMC based on CH4 CMC based on O2 Strained flamelet G-equation

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Experiment: Chen et al., Combustion and Flame 107, 1996

Progress variable0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

dc/d

r (1/

m)

0

50

100

150

200

250

X/D=2.5 X/D=4.5 X/D=6.5 X/D=8.5 X/D=10.5

δ t =∂ !c∂r

⎛⎝⎜

⎞⎠⎟−1

max

[1] Kolla et al., Combustion and Flame 157, 2010[2] Herrmann et al., Combustion and Flame 145, 2006

1

12

▪ Turbulent flame thickness



19


premixed combustion


CMC premixed

CMC non-premixed

mode transition

CMC non-premixed

CMC premixed




Multi-mode CMC: model formulation

0, high Re flows

PDF gradient model (Pope 1985)AMC model (Nguyen 2010)

algebraic mean or neglectedalgebraic model (Kolla 2010)

first order closure (Bilger 2004) Bilger 1993

▪ …just to give an idea about the model complexity

‣ Boundary and initial conditions? ‣ Probability Density Function (PDF) models? Cross-PDF? ‣ etc.


Conclusions & Outlook

▪ Towards a complex formulation for multiple combustion modelling, two numerical frameworks have been first established: ‣ CMC for non-premixed combustion has been carefully validated over a

broad range of conditions showing promising results ‣ CMC for premixed combustion has been formulated and recently

implemented • A first validation work has been conducted for canonical problems • Other configurations will be simulated (spark ignited flames, real engines

geometry)

▪ Next step is the coupling of the two models for a double-conditioned CMC formulation (ongoing work) ‣ A priori DNS studies will be conducted

‣ Double-conditioned CMC will be validated with DNS data


Acknowledgments

Financial support from the

Swiss Federal Office of Energy (BfE)

and the

Swiss Competence Centre Energy and Mobility (CCEM)

is gratefully acknowledged.

The authors further thank

Prof. Mastorakos and Prof. Swaminathan (Cambridge University)

for very helpful discussions.

Thank you for your kind attention!

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Dual-fuel Concept & Formulation - ETH Zürich · PDF fileTowards modelling of multiple combustion modes: Dual-fuel Concept & Formulation. ... Reduced emissions that can satisfy the