In-cylinder flows and combustion modeling: application and validation to real and enginelike configurations

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Chloe Wilson
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1 Second Two-Day Meeting on Internal Combustion Engine Simulations Using the OpenFOAM technology, Milan th November 216. In-cylinder flows and combustion modeling: application and validation to real and enginelike configurations T. Lucchini, G. D'Errico, A. Della Torre, T. Cerri, A. Maghbouli, E. A. Tahmasebi, L. Sforza, D. Paredi Politecnico di Milano, Department of Energy

2 Topics 2 In-cylinder flows and combustion modeling using OpenFOAM technology OpenFOAM Lib-ICE CFD methodologies Validation Application Next steps

3 Lib-ICE 3 Internal combustion engine modeling using the OpenFOAM technology OpenFOAM-x.x.x Engine simulation workflow Mesh generation Development/validation Lib-ICE Fuel-air mixing Spray modeling Library: physical models, mesh management Engine flows Applications: solvers (cold flow, SI, Diesel, aftertreatment), utilities Combustion Diesel combustion SI combustion

4 Engine simulation workflow 4 Methodology Diesel engines Mesh management Cold flow Fuel-air mixing Combustion SI engines

5 Engine simulation workflow 5 Methodology Diesel engines Mesh management Cold flow Fuel-air mixing Combustion SI engines Automatic mesh generation Mesh motion Topological changes Discretization Turbulence models Mesh quality Lagrangian spray Sub-models Nozzle flow Simplified or detailed kinetics Ignition Pollutants

6 Engine simulation workflow 6 Methodology Diesel engines SI engines Fully integrated approaches Mesh management Automatic mesh generation Mesh motion Topological changes Cold flow Discretization Turbulence models Mesh quality Fuel-air mixing Lagrangian spray Sub-models Nozzle flow Open-Source code Combustion Simplified or detailed kinetics Ignition Pollutants

7 Diesel Engines

8 Diesel engines 8 Methodology / model development Engine CAD data Nozzle flow Combustion models Automatic mesh generation Mesh handling Cold flow Spray models

9 Diesel engines 9 Mesh management Automatic mesh generation a) Main engine data b) Spray oriented block mesh Mesh handling Dynamic layering d) Spray-oriented mesh c) Combustion chamber points fit

10 Diesel engines 1 Mesh management Automatic mesh generation a) Main engine data b) Spray oriented block mesh Mesh handling Dynamic layering Bowl #1 Bowl #2 Bowl #3 Bowl #4 Bowl #5 Bowl #6 d) Spray-oriented mesh c) Combustion chamber points fit From CAD to SIMULATION: 1 minutes

Average Liquid Length [mm] 18 mm Mixture Fraction [-] 2d computational mesh Diesel Engines: spray modeling 11 Spray A from Engine Combustion Network Spray model setup

inj : 5-15 MPa T amb : 7-12 K r amb : 7.6 22.8 kg/m 3 Baseline (p inj = 15 MPa; T amb = 9 K; r amb = 22.8 kg/m 3 ) Dashed: exp Continuous: calc.

11 Average Liquid Length [mm] 18 mm Mixture Fraction [-] 2d computational mesh Diesel Engines: spray modeling 11 Spray A from Engine Combustion Network Spray model setup Injection: blob Breakup: KHRT Evaporation: Spalding CFD setup Turbulence model: standard k-e with modified C 1 Test conditions Fuel n-dodecane Nozzle diameter: 9 mm p inj : 5-15 MPa T amb : 7-12 K r amb : kg/m 3 Baseline (p inj = 15 MPa; T amb = 9 K; r amb = 22.8 kg/m 3 ) Dashed: exp Continuous: calc. Liquid Vapor z = 22.5 mm Exp PoliMI z = 45 mm Distance from axis [mm] Parametric variations (T amb, r amb ) Experimental Computed Ambient Temperature [K]

12 Diesel Engines: spray modeling 12 FPT C11 Spray (collaboration with TU/e DI N. Maes and Prof. B. Somers, FPT support) TU/e optical vessel 3D mesh (a) CFD Setup (b) Validation Liquid: exp vs computed extinction profiles Liquid penetration: DBI Vapor penetration: Schlieren Operating conditions Nozzle diameter:.25 mm Ambient temperature: 9 K ANR C1 C2 P inj [MPa] r amb [kg/m 3 ] Consistent with the engine grid in size and structure Spray Huh-Gosman atomization Pilch-Erdman breakup Turbulence modeling k-e with modified C 1

13 Diesel Engines: spray modeling 13 FPT C11 Spray (collaboration with TU/e DI N. Maes and Prof. B. Somers, FPT support) TU/e optical vessel 3D mesh (a) CFD Setup (b) Validation Liquid: exp vs computed extinction profiles Liquid penetration: DBI Vapor penetration: Schlieren Operating conditions Nozzle diameter:.25 mm Ambient temperature: 9 K ANR C1 C2 P inj [MPa] r amb [kg/m 3 ] Consistent with the engine grid in size and structure Spray Huh-Gosman atomization Pilch-Erdman breakup Turbulence modeling k-e with modified C 1

Vapor penetration: Schlieren Operating conditions Nozzle diameter:.25 mm Ambient temperature: 9 K ANR C1 C2 P inj [MPa] 15 8 15 r amb [kg/m 3 ] 22.

14 Diesel Engines: spray modeling 14 FPT C11 Spray (collaboration with TU/e DI N. Maes and Prof. B. Somers, FPT support) TU/e optical vessel 3D mesh (a) CFD Setup (b) Validation Liquid: exp vs computed extinction profiles Liquid penetration: DBI Vapor penetration: Schlieren Operating conditions Nozzle diameter:.25 mm Ambient temperature: 9 K ANR C1 C2 P inj [MPa] r amb [kg/m 3 ] Consistent with the engine grid in size and structure Spray Huh-Gosman atomization Pilch-Erdman breakup Turbulence modeling k-e with modified C 1 Vapor: exp (Schlieren), calc. (mixture fraction threshold)

Diesel Engines: cold flow 15 Steady state flow bench

Setup Steady-state flow Turbulence model: standard k-e Porous

computation of the swirl torque Verification of angular

Cartesian, body fitted grids with boundary layer generated with

15 Diesel Engines: cold flow 15 Steady state flow bench simulations (FPT Industrial, Gilles Hardy) Mesh generation CFD Setup Steady-state flow Turbulence model: standard k-e Porous media acts as a flow straigthner in the computational mesh: computation of the swirl torque Verification of angular momentum conservation across the mesh boundaries. Cartesian, body fitted grids with boundary layer generated with cartesianmesh (cfmesh) or snappyhexmesh (OpenFOAM) This work was part of Davide Paredi MSc Thesis

Diesel Engines: cold flow Steady state flow bench

flow field.8.6.4.2 Lift = 5 mm Flow coeff. C.

16 Diesel Engines: cold flow Steady state flow bench simulations (FPT Industrial, Gilles Hardy) Computed flow field Lift = 5 mm Flow coeff. C.8 d [-] Lift = 1 mm Exp. Calc Swirl number N s [-] from Torque Lift = 5 mm Lift = 1 mm Exp. Calc. This work was part of Davide Paredi MSc Thesis

17 Diesel Engines 17 Combustion modeling Characteristic time-scale model (CTC) Well-mixed model Medium-duty engine operating at low-load with iso-octane fuel. Passenger-car Diesel engine mrif model N-dodecane spray combustion at constant volume conditions ECN Spray-A experiment Variation of ambient temperature, density, oxygen and injection pressure Kinetic mechanism: Luo et al. (111 species, 467 reactions) Ignition delay Density Inj. Press. O 2 conc. Amb. Temp Computed Experimental

18 Diesel Engines 18 Combustion modeling Characteristic time-scale model (CTC) Well-mixed model Medium-duty engine operating at low-load with iso-octane fuel. Passenger-car Diesel engine mrif model N-dodecane spray combustion at constant volume conditions ECN Spray-A experiment Variation of ambient temperature, density, oxygen and injection pressure Kinetic mechanism: Luo et al. (111 species, 467 reactions) Flame lift-off Density Inj. Press. O 2 conc. Amb. Temp Computed Experimental

Diesel Engines: validation 19 Spray B in Engines (from

Musculus) Optically accessible engine with three hole

reacting Liquid length Vapor distribution CALC.

possibility to perform same studies in engine and

This work is part of Amin Maghbouli PhD project Same

combustion models tested: mrif and well-mixed.

19 Diesel Engines: validation 19 Spray B in Engines (from ECN, collaboration with Dr. Eagle, Dr. Malbec, Dr. Musculus) Optically accessible engine with three hole injector CFD setup and tested points Validation: non reacting Liquid length Vapor distribution CALC. CALC. Nozzle design very similar to spray A: possibility to perform same studies in engine and constantvolume vessel. This work is part of Amin Maghbouli PhD project Same CFD setup used in Spray A simulations, two different combustion models tested: mrif and well-mixed. Tested conditions T@SOI: 8-1 K P inj [bar]: 5 15 bar O 2 [%]: % SOI: kg/m 3 Fuel: n-dodecane EXP EXP

20 Diesel Engines: validation 2 Spray B in Engines (from ECN, collaboration with Dr. Eagle, Dr. Malbec, Dr. Musculus) Optically accessible engine with three hole injector CFD setup and tested points Validation: reacting Nozzle design very similar to spray A: possibility to perform same studies in engine and constantvolume vessel. This work is part of Amin Maghbouli PhD project Automatically generated grid Same CFD setup used in Spray A simulations, two different combustion models tested: mrif and well-mixed. Tested conditions T@SOI: 8-1 K P inj [bar]: 5 15 bar O 2 [%]: % SOI: kg/m 3 Fuel: n-dodecane

21 Diesel Engines: validation 21 EU 6 FPT Engine MD (support from FPT, DI Gilles Hardy) Cylinder pressure validation (mrif and well-mixed) 75% load, 15% EGR, 2 injections 4 14 Exp. m-rif Exp. 4 Grid automatically generated Crank Angle [deg] Initial conditions from 1D simulations 5 Well-mixed 35 7 Pressure [bar] 3 m-rif [rpm] 4 9 Well-mixed 12 Pressure [bar] 8 25% load, 2% EGR, 3 injections Heat release rate [J/kg] bmep/bmepmax Crank Angle [deg] 5 Heat release rate [J/kg] Five operating points: with different EGR levels

22 Diesel Engines: validation 22 EU 6 FPT Engine MD (support from FPT, DI Gilles Hardy) Cylinder pressure validation (mrif and well-mixed) 1% load, 35% EGR, 3 injections 4 7 Exp. m-rif Exp. 3 4 Grid automatically generated Crank Angle [deg] Initial conditions from 1D simulations 5 Pressure [bar] 35 5 [rpm] 4 16 Well-mixed 6 Pressure [bar] 8 Full load, % EGR, 1 injection Heat release rate [J/kg] bmep/bmepmax 1 m-rif Well-mixed Crank Angle [deg] 5 Heat release rate [J/kg] Five operating points: with different EGR levels

23 Cyl. Pressure [bar] Heat Release Rate [J/deg] Diesel Engines: validation 23 PCCI engine (support from FPT, DI Gilles Hardy) PCCI combustion conditions Combustion model: Well-mixed High EGR rate (5%) 3 rpm Exp Exp. Computational mesh generated automatically with the Polimi tool Well-mixed Well-mixed Crank Angle [deg] Crank Angle [deg] Diesel fuel: n-dodecane Kinetic mechanism: Faravelli et al. (11 species, 3 reactions)

24 PCCI combustion conditions High EGR rate (5%) 3 rpm Computational mesh generated automatically with the Polimi tool Diesel Engines: validation 24 PCCI engine (support from FPT, DI Gilles Hardy)

25 NOx (normalized) soot (normalized) Diesel Engines: validation 25 Heavy Duty engines (support from GE Global Research, Dr. Pasunurthi) Automatic mesh generation Operating conditions SOI variation Soot/NO x trade-off Dual-fuel combustion Diesel: mrif Dual-fuel: PaSR NOx: Zeldovich, soot: Moss P cyl /P max Conventional Diesel Combustion Engine 1: SOI variation SOI #1, Exp. SOI #1, Calc. SOI #2, Exp. SOI #2, Calc. SOI #3, Exp. SOI #3, Calc Crank Angle [deg] p/p max Engine 2: pollutant prediction OP Crank Angle [deg] Exp. Calc. p/p max OP.3 Calc. Exp. OP.1 OP.2 OP Crank Angle [deg] Exp. Calc.

26 Diesel Engines validation 26 Heavy Duty engines (support from GE Global Research, Dr. Pasunurthi) Setup Reduced mechanism for Diesel (C 7 H 16 ) and natural gas Combustion model: PaSR Dual-fuel combustion RoHR/RoHR max OP 1 Validation Exp. Calc. RoHR/RoHR max OP 2 Exp. Calc. Pollutants NO x : Zeldovich Soot: Moss Two operating points: same air/fuel ratio, different amount of injected Diesel fuel Crank Angle [deg] Crank Angle [deg] 1.2 Exp. 1 Calc..8 NO x / NO x,max OP 1 OP 2

single hole injectors are defined by ECN to

72 spray results C mdot (g/s) spray D mdot

51 POLIMI Presssure across the hole axis and

kinetics: Homogeneous reactors Unsteady RIF

27 Internal nozzle flow modeling (RANS, cavitation) Spray C & Spray D These two single hole injectors are defined by ECN to compare the effect of geometry on flow behavior. Spray C Spray D Spray C Diesel Engines 27 Next steps ECN contributors spray results C mdot (g/s) spray D mdot (g/s) Experiments 1.51 POLIMI Presssure across the hole axis and more mrif with multiple injections Tabulated kinetics: Homogeneous reactors Unsteady RIF blockmesh grid Spray C k factor=, sharp edge Spray D k factor=1.5, rounded edge Spray C cavitated Spray D Not cavitated Transported PDF combustion modeling: Eulerian Stochastic fields with tabulated kinetics! This work is part of Ehsan Tahmasebi PhD project

28 SI Engines

29 SI Engines 29 Methodology / model development Engine CAD data Nozzle flow Combustion models Automatic mesh generation Mesh handling Cold flow Spray models

30 SI Engines: cold flow 3 Darmstadt optical engine (collaboration with Dr. B. Bohm and DI C. P. Ding) Velocity Magnitude (m/s) Four-valve engine, fully optically accessible PIV measurement techniques: low repetition rate planar PIV high-speed PIV (HS-PIV) stereoscopic PIV (SPIV) tomographic PIV (TPIV).

31 Lift [mm] SI Engines: cold flow 31 Full cycle SI: Darmstadt optical engine automatic mesh generation STL + data Geometry-oriented block structured mesh snappyhexmesh Exhaust Intake Crank Angle [deg] Bore 8 mm Stroke 6 mm Conrod 16 mm The user provides combustion chamber geometry and data (bore, stroke, valve lifts) A python program automatically recognizes the direction of ducts, cylinder and valves and generates a geometryoriented background grid snappyhexmesh is then run using the geometry-oriented background mesh

Lift [mm] SI Engines: cold flow 32 Full cycle SI: Darmstadt optical

structured mesh snappyhexmesh 1 7.5 Exhaust Intake 5 2.

The user provides combustion chamber geometry and data (bore,

direction of ducts, cylinder and valves and generates a

32 Lift [mm] SI Engines: cold flow 32 Full cycle SI: Darmstadt optical engine automatic mesh generation STL + data Geometry-oriented block structured mesh snappyhexmesh Exhaust Intake Crank Angle [deg] Bore 8 mm Stroke 6 mm Conrod 16 mm The user provides combustion chamber geometry and data (bore, stroke, valve lifts) A python program automatically recognizes the direction of ducts, cylinder and valves and generates a geometryoriented background grid snappyhexmesh is then run using the geometry-oriented background mesh

SI Engines: cold flow 33 Full cycle SI: Darmstadt optical engine mesh management

Duration of each mesh: - User defined + quality criteria Initial mesh at Crank

for Dq Mesh quality and duration satisfied?

33 SI Engines: cold flow 33 Full cycle SI: Darmstadt optical engine mesh management Full-cycle simulations: - Multiple meshes - Mesh to mesh interpolation strategy. Duration of each mesh: - User defined + quality criteria Initial mesh at Crank angle q q = q curr Generate a new mesh with snappyhexmesh q curr = q Move mesh for Dq Mesh quality and duration satisfied? NO q curr = q curr + Dq YES Move surface geometry to current crank angle q curr NO YES q curr = q end? End of meshing

34 SI Engines: cold flow 34 Full cycle SI: Darmstadt optical engine case setup Models and boundary conditions Engine geometry data Bore Stroke 86 mm 86 mm Compression ratio 8.5 IVO IVC EVO EVC Speed Combustion 325 CAD 485 CAD 15 CAD 345 CAD 85 rpm no Boundary conditions Unsteady boundary conditions (from exp. data) imposed at inlet and outlet ports. CFD models Second-order discretization (TVD) Turbulence model: standard k-e

cylinder head, piston and liner boundaries; local refinement up to.25 mm close to the valves boundaries.

35 SI Engines: cold flow 35 Full cycle SI: Darmstadt optical engine case setup Computational mesh Mesh layouts 4 mm mesh size in the ducts region; 2 mm mesh size in the cylinder and valve region; local refinement up to 1 mm close to cylinder head, piston and liner boundaries; local refinement up to.25 mm close to the valves boundaries. a) Cartesian mesh (automatically generated + snappyhexmesh) b) Flow-oriented mesh (automatically generated + Polimi tool + snappyhexmesh)

36 SI Engines: cold flow 36 Full cycle SI: Darmstadt optical engine validation

37 U y [m/s] SI Engines: cold flow 37 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the cylinder head. 45 CAD mid-intake Similar behavior between the two grids, flow dominated by the incoming air jet Experimental Cartesian Flow-oriented Y = mm Y = -1 mm Y = -2 mm Y = -3 mm -1 y -2-3 x Flow-oriented Cartesian Experimental

38 U x [m/s] SI Engines: cold flow 38 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the cylinder head. 45 CAD mid-intake Similar behavior between the two grids, flow dominated by the incoming air jet Experimental Cartesian Flow-oriented Y = mm Y = -1 mm Y = -2 mm Y = -3 mm -1 y -2-3 x Flow-oriented Cartesian Experimental

39 U y [m/s] SI Engines: cold flow 39 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the cylinder head. 54 CAD BDC, intake Better prediction of the flow oriented grid: Vortex location, distribution of the two main streams Experimental Cartesian Flow-oriented Y = mm Y = -1 mm Y = -2 mm Y = -3 mm -1 y -2-3 x Flow-oriented Cartesian Experimental

U x [m/s] SI Engines: cold flow 4 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the

40 U x [m/s] SI Engines: cold flow 4 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the cylinder head. 54 CAD BDC, intake Better prediction of the flow oriented grid: Vortex location, distribution of the two main streams Experimental Cartesian Flow-oriented Y = mm Y = -1 mm Y = -2 mm Y = -3 mm -1 y -2-3 x Flow-oriented Cartesian Experimental

U y [m/s] SI Engines: cold flow 41 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the

41 U y [m/s] SI Engines: cold flow 41 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the cylinder head. 66 CAD mid-compression Flow-oriented grid better describe the tumble vortex structure Experimental Cartesian Flow-oriented Y = mm Y = -1 mm Y = -2 mm Y = -3 mm -1 y -2-3 x Flow-oriented Cartesian Experimental

42 U x [m/s] SI Engines: cold flow 42 Full cycle SI: Darmstadt optical engine validation x and y velocity components along four different measurement lines located at different distances from the cylinder head. 66 CAD mid-compression Flow-oriented grid better describe the tumble vortex structure Experimental Cartesian Flow-oriented Y = mm Y = -1 mm Y = -2 mm Y = -3 mm -1 y -2-3 x Flow-oriented Cartesian Experimental

Montanaro) Optically accessible GDI engine Injection pressure [bar]

43 SI Engines: GDI fuel-air mixing 43 Stratified engine (collaboration with IM-CNR, Ing. Sementa, Ing. Montanaro) Optically accessible GDI engine Injection pressure [bar] Operating points SOI [ BTDC] Charge stratification High Low High Low bmep = 7.2 bar, SA = 13 BTDC; l = 1.15 (lean)

SI Engines: GDI fuel-air mixing 44 Stratified engine

12 = 6 bar; SOI = 7 BTDC Possible sources of soot: Rich

44 SI Engines: GDI fuel-air mixing 44 Stratified engine Optically accessible GDI engine: optical/computed data correlation Fuel m.f. P inj = 1 bar; SOI = 11 BTDC Soot chemiluminescence P inj.12 = 1 bar; SOI = 11 BTDC Fuel m.f. P inj = 6 bar; SOI = 6 BTDC Soot chemiluminescence P inj.12 = 6 bar; SOI = 7 BTDC Possible sources of soot: Rich pockets Wall-film Correlated with optical soot chemiluminescence Wall-film l distribution Wall-film l distribution

SI Engines: combustion 45 Modeling Comprehensive combustion model

approach and suitable sub-models (breakdown, electrical circuit,

Eulerian phase (gas) Strict coupling between Eulerian and Lagrangian

Spark gap hq el r i Breakdown T i (>1 K) T u (3-6 K) Flame surface

spark-channel Mass and energy equations solved for the flame kernel

restrike Possibility to predict the effects of local flow, mixture

45 SI Engines: combustion 45 Modeling Comprehensive combustion model Detailed description of the flame kernel growth process via Lagrangian approach and suitable sub-models (breakdown, electrical circuit, wrinking) Coherent flamelet model for flame propagation in the Eulerian phase (gas) Strict coupling between Eulerian and Lagrangian phases Sub-models Secondary circuit energy transfer R p R s L p L s Spark gap hq el r i Breakdown T i (>1 K) T u (3-6 K) Flame surface density spk N f i 1 i S i V cell Lagrangian particles for the spark-channel Mass and energy equations solved for the flame kernel particles Particles convected by the flow, possibility to predict restrike Possibility to predict the effects of local flow, mixture conditions, turbulence, electrical circuit properties (voltage, current). Prediction of misfire also possible.

SI Engines: combustion 46 Assessment and validation

Multi-ignition systems Fan-generated flow velocity and

stage (Lagrangian Eulerian coupling) Fully turbulent

46 SI Engines: combustion 46 Assessment and validation Applications Results Pressurized vessels Multi-ignition systems Fan-generated flow velocity and turbulence fields at the spark-gap Initial combustion stage (Lagrangian Eulerian coupling) Fully turbulent flame (Eulerian model only) This work is part of Lorenzo Sforza PhD project

Enflammed volume [cm 3 ] Enflammed volume [cm 3 ] SI Engines:

field, flame propagation and plasma temperature details 2 1.6 1.

6 1.2 Calc., 1 rpm, l = 1. Calc., 3 rpm, l = 1. Calc., 125 rpm, l = 1.

47 Enflammed volume [cm 3 ] Enflammed volume [cm 3 ] SI Engines: combustion 47 Experimental validation: Herweg and Maly Engine Flow field, flame propagation and plasma temperature details Calc., 1 rpm, l = 1. Calc., 1 rpm, l = 1. Exp., 1 rpm, l = 1. Exp., 1 rpm, l = Calc., 1 rpm, l = 1. Calc., 3 rpm, l = 1. Calc., 125 rpm, l = 1. Exp., 1 rpm, l = 1. Exp., 3 rpm, l = 1. Exp., 125 rpm, l = 1..8 Peripheral Central Time after spark [ms] This work is part of Lorenzo Sforza PhD project Time after spark [ms]

Conclusions 48 CFD modeling of in-cylinder

Consolidated methodologies, currently applied

48 Conclusions 48 CFD modeling of in-cylinder phenomena at Polimi with OpenFOAM Detailed models continuously validated and improved: Fundamental studies Applied research Consolidated methodologies, currently applied in the context of industrial collaborations but there is still a lot to do!

49 Thanks for your attention!

Gas exchange and fuel-air mixing simulations in a turbocharged gasoline engine with high compression ratio and VVA system

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