S. S. Pandurangi* N. Frapolli D. Farrace DIESEL …...Pandurangi, Frapolli, Bolla, Boulouchos &...
Transcript of S. S. Pandurangi* N. Frapolli D. Farrace DIESEL …...Pandurangi, Frapolli, Bolla, Boulouchos &...
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DIESEL ENGINES AND SPRAYS COMBUSTION MODELLING
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Enhancement of soot oxidation rate - order of magnitude enhancement at high EGR (larger soot volume) - caused by additional locally available oxygen - soot evolution of the low-EGR case shows an initial increase due to ad-
ded fuel, but subsequent drop due to improved oxidation
O2 difference (normalised by the O2 distribution of the single-injection case) shows an accumulation of O2 at the tip of the post-injection being pushed into the main flame.
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S. S. Pandurangi* N. Frapolli D. Farrace M. Bolla Y. M. Wright K. Boulouchos*
Influence of EGR on Post-injection Effectiveness in a Heavy-duty Diesel Engine
IntroductionSoot particles emitted by diesel engines are dan-gerous for the enviroment and for living organ-isms. Emission legislation around the world is be-coming increasingly stringent, demanding better understanding of the physics of soot formation to design countermeasures. One such measure being heavily researched is the addition of a small fuel post-injection. In this numerical study based on data from a heavy-duty research diesel engine [1], we investigate the effect of post-injection on soot evolution and governing processes, and the influence of exhaust gas recirculation on the in-teraction between post- and main- injections.
Soot model: two-equations model [6]
CFD modelCFD computational setup:
• Commercial CFD code STAR-CD [2]• 2D grid with 1.0 mm mesh size• k-epsilon turbulence model, wall functions• Euler-Langrange approach for droplets• Coditional Moment Closure (CMC) combus-
tion model [3]• Reduced mechanism for n-heptane [5]• Two-equations soot model [6]• Optical-thin soot radiation model [7]• Soot differential diffusion effects neglected
(Le=1)
Experimental setup [1]
Solve transport equations for soot mass fraction and soot number density (Le=1):
Source term soot mass fraction:
Source term soot number density:
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2 2ω 10 [ ] TINCP C H e−
=
121003
2 2ω 6 10 [ ] TSUR GROW sootC H e A−
= ⋅ ⋅
2
190004
2ω 10 [ ]OT
OXID sootO e T A−
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ω 0.36[ ]OHOXID soot
OH T A= ⋅ ⋅
( )1 1
111 12 662 6
24 6ω 3COAG S SS A S
R T Y NN
ρρ πρ
= −
nnP P→
(1) Particle inception:
(2) Particle surface growth( ) ( ) ( )2 2 22S SC H nC n C H+ → + +
(3) Particle oxidation by O2:
(4) Particle oxidation by OH:
(5) Particle coagulation:
( )2 2 22 SC H C H→ +
( ) 21
2SC O CO+ →
( )SC OH CO H+ → +
ACETYLENE
PRODUCTS
Nucleation (1)
Coagulation (5)SurfaceGrowth
(2)
Surface oxidation (3-4)
FUEL
Reduced n-Heptanemechanism (0)
( ) ( )2
2
1i i
i i
Q Q Qu N u Y P wt x P xα α α
α αη η ρ η η ηη ρ η∂ ∂ ∂ ∂ ′′ ′′+ − + = ∂ ∂ ∂ ∂
2, , , ,S S S S SY Y inception Y growth Y oxidationO Y oxidationOHw w w w wη η η η η= + + +
, ,S S SN N inception N coagulationw w wη η η= +
Soot model accouts for simultaneous soot particle inception, surface growth, oxidation by O2 and OH and coagulation
Governing equations [3]
4 44RAD soot Wallw T Tη σα η = − −
First order closure for source terms
Linear model for conditional velocity
Gradient flux
AMC model for scalar dissipation rate
Optically-thin radiation model [7]12370SOOTsoot V
f TmK
α = ⋅ ⋅
References
Acknowledgements
[1] O‘Connor, J. and M. Musculus. International Journal of Engine Research, 2013.
[2] CD-adapco, STAR-CD v4.16, 2010.[3] A. Y. Klimenko and R. W. Bilger. Progress in Energy
and Combustion Science, vol. 25, pp. 595-687, 1999.[4] Y. M. Wright, et al. Combustion and Flame, vol. 143,
pp. 402-419, 2005.[5] S. L. Liu, et al., Combustion and Flame, vol. 137, pp.
320-339, 2004.[6] K. M. Leung, et al. Combustion and Flame, vol. 87,
pp. 289-305, 1991.[7] J. F. Widmann. Combustion Science and Technology,
vol. 175, pp. 2299-2308, 2003.[8] Bolla, M., et al. International Multidimensional En-
gine Modeling Users‘ Group Meeting 2014
Funding• Competence Center for Energy and Mobility
(CCEM-CH) project “In-cylinder emission re-duction for large diesel engines”
• Swiss Federal Office of Energy (BfE)
Engine heat release and flowfield validation
Soot formation and oxidation processes
Engine parametersbore: 140 mm (VH=2.34 L)CR=11.2(geom.), 16(sim.)swirl ratio: 0.5injector: 8 x 0.131 mmfuel: n-heptaneMeasurement techniquespressure & AHRR2D natural luminosityplanar LII
Multiple Injections [8]10 5 0 5 10 15 20
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21% O2 18% O2
12.6% O215% O2
+12 °CA
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+13 °CA
Expt. Soot NL CFD Integrated FvS
Pandurangi, Frapolli, Bolla, Boulouchos & Wright. Influence of EGR on Post-Injection Effectiveness in a Heavy-Duty Diesel Engine Fuelled with n-Heptane. SAE 2014-01-2633.
Relative oxygen field for the post-injection case compared to the single-injection case
Soot-quantities for single- and post-injection
at high EGR (12.5% O2) at low EGR (18% O2)
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Soot evolution at low EGR (18% O2)
• very good accuracy maintained considering the large dilution spread
• overestimations of AHRR of the main injection strongly influence the ignition and heat release from the ‹sensitive› post-injection
• excellent prediction of the positi-on of the post-injection soot with respect to penetration and orien-tation
• impingement on the wall and subsequent curling qualitatively well captured
Interfacing of CFD and CMC code [4]:
Multiple injections using a single total mixture fraction (MFT) as the conditioning scalar.re-initialisation of conditional tempe-rature and composition in every CMC cell at the time of the first appea-rance of MF from post injection (MF2) constraint: MF1 + MF2 = MFT