Improved Modelling of DI Diesel Engines Using Sub ...

Improved Modelling of DI Diesel Engines Using Sub-grid Descriptions of Spray and Combustion P. BEARD, O. COLIN and M. MICHE IFP, Rueil-Malmaison, France

Work supported by GSM: IFP, Peugeot, Renault

Presentation
Sub-grid

models

hSpray hCombustion Results hDiesel simulation cell hDI Diesel engine Conclusion 2

2003-01-0008

Spray model (CLE) Coupled Lagrangian-Eulerian model (SAE 2000-01-1893) Goals :
To reduce the mesh sensitivity of HP DI spray modelling,
To improve the simulation of combustion in DI Diesel (DID) engines. Similar approaches (1D) : - Wan & Peters (SAE 972866) : Cross-section Averaged Spray - Abraham & Magi (SAE 1999-01-0911) : Virtual Liquid Source 3

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Description of the CLE model KMB

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Description of the CLE model KMB

KMB + CLE model

⇒ Over-estimated diffusion ! 5

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Description of the CLE model KMB

KMB + CLE model

⇒ Over-estimated diffusion !

⇒ Reduced diffusion 6

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Combustion model (ECFM3Z) Extended Coherent Flame Model 3 Zones = ECFM (Oil & Gas Science and Tech., 2003) + CFM3Z (to be published in Comb. Science and Tech.) Goals :
To account for the local fuel stratification,
To describe the mixing process between fuel and air. Similar model : Bensler, Bühren, Samson & Vervisch (SAE 200001-0662) : Ricardo Two Zone Flamelet

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Description of the ECFM3Z model Sub-grid description of the local stratification : 3 zones Air (+ EGR)

Equivalence ratio

Turbulent mixing

Mixed zone

Fuel

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Description of the ECFM3Z model Sub-grid description of the local stratification

Homogeneous reactor

Air (+ EGR)

Equivalence ratio

Auto-ignition

Mixed zone

Turbulent mixing

Fuel

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Description of the ECFM3Z model Sub-grid description of the local stratification

Homogeneous reactors

Air (+ EGR) Mixed zone Equivalence ratio

Fresh

Burnt

gases

gases

Turbulent mixing

Auto-ignition

Fuel Premixed flame (oxidation) 10

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Description of the ECFM3Z model Sub-grid description of the local stratification

Homogeneous reactors

Air (+ EGR) Mixed zone Equivalence ratio

Fresh

Burnt

gases

gases

Turbulent mixing

Auto-ignition

Fuel Premixed flame (oxidation) 11

Diffusion flame (oxidation+pollutant formation) 2003-01-0008

Computer code KMB (KIVA Multi-Blocks) based on KIVA-II
Turbulence model : k-ε Open structured blocks (with refinement)

Atomization : Wave-FIPA (SAE 970881)
Spray/wall interaction, liquid film transport and evaporation (Oil & Gas Science and Tech., 1999)





Pollutant formation : q NO

Moving walls

: extended Zeldovitch q Soot : 10 reaction mechanism (SAE 2001-01-3684)

Same constants for all runs 12

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Presentation Sub-grid models hSpray hCombustion
Results

hDiesel simulation cell hDI Diesel engine Conclusion 13

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Diesel simulation cell Fuel : C12H26 Pinj ≤ 200 MPa, Dinj ≤ 200 µm

Injector

Window

Pch ≤ 15 MPa, Tch ≤ 1500 K

At SOI (Start Of Injection) : Vgas ≈ 0 m/s, k ≈ 0.06 m2/s2

Corner access port

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Mesh sensitivity of the spray model Pinj = 80 MPa, Pch = 6 MPa, Tch = 800 K KMB + CLE model

Fuel vapor mass fraction 0 ≤ Yv ≤ 0.2

⇒ Reduced mesh sensitivity

∆x = 1 mm ∆z = 2.7 mm 15

∆x = 1 mm ∆z = 1.3 mm

∆x = 0.5 mm ∆z = 1.3 mm

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Mesh sensitivity of the spray model Pinj = 80 MPa, Pch = 6 MPa, Tch = 800 K KMB KMB + CLE model

∆x = 2 mm ∆z = 2.7 mm

∆x = 1 mm ∆z = 2.7 mm 16

∆x = 1 mm ∆z = 1.3 mm

∆x = 0.5 mm ∆z = 1.3 mm

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DI Diesel engine Peugeot passenger car engine

3D grid : ≈ 250 000 cells at BDC Simulation from IVO (intake TDC) to EVO (140 deg. ATDC)

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DID engine piston geometry Piston bowl shapes

Constant compression ratio = 18 Cell size inside the bowl ≈ 1 mm 18

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DID engine operating conditions


21 cases were computed

Engine speed (rpm) : Load : Global equivalence ratio : SOI (deg. BTDC) : EGR (%) :

1250, 1640, 4000 full or partial [0.46;0.83] 3, 5, 15, 29 [0;30]

Jet Wall Impact parameter (mm) : defined at TDC (SAE 2002-01-0495)

[3.3;8.9]

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Influence of sub-grid models Case A : 4000 rpm, full load (Φ = 0.71), bowl 2

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Influence of piston bowl shape Case B : 4000 rpm, full load (Φ = 0.71), bowl 3

Relative variations between cases A and B : - indicated power : measured -3 %, computed -6 % - soot emissions : measured +11 %, computed +18 % 21

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Influence of JWI parameter (1) Case C8 (JWI = 8.1 mm) : 4000 rpm, full load (Φ = 0.71), bowl 1 KMB

KMB + CLE + ECFM3Z

Fuel vapor mass fraction 22

0 ≤ Yv ≤ 0.2

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Influence of JWI parameter (2) Case C : 4000 rpm, full load (Φ = 0.71), bowl 1

-7 %

∆zinj = 0.9 mm

-10 %

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Influence of EGR (1) Case F : 1640 rpm, partial load, bowl 2 Experiment

KMB + CLE + ECFM3Z

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Influence of EGR (2) Case F : 1640 rpm, partial load, bowl 2

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Computed

Soot emissions (mg/s)

Measured

NO emissions (mg/s)

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Influence of pilot injection Case H : 1640 rpm, partial load (Φ = 0.64), 20% EGR, bowl 2

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Conclusions (1) New sub-grid models CLE and ECFM3Z are applicable for DID engine simulations with multi-hole injectors and multi-injections. ⇒ Reduced mesh sensitivity of the spray model. ⇒ Without any tuning, improved prediction of hthe influence of operating conditions (engine speed and load, bowl shape, nozzle tip protrusion, EGR, pilot injection) on DID engine performance. hthe sensitivity of pollutant (NO, CO and soot) emissions. 27

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Conclusions (2) The new sub-grid models were successfully used to optimize the design of HCCI engines. Nevertheless, relative variations between cases are sometimes under or over-estimated. ⇒ Additional developments are still required to become fully predictive : hCalculation of an auto-ignition delay accounting properly for the ambient conditions, in particular high EGR rates. hDescription of the mixing process between fuel and air.

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