ECN4 – Diesel Combustion REACTIVE FLOW ANALYSIS Coordinator: José M. García-Oliver, CMT September 6th, 2015

MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS CONTENTS MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS EXPERIMENTS VS CALCULATION Inert flow Reacting flow – Nominal spray A Reacting flow – Low reactivity cases CONCLUSIONS

MOTIVATION Existence of a database of PIV measurements by IFPEN available for CFD validation 900K, 22.8kg/m3, 0%O2 900K, 22.8kg/m3, 15%O2 Ref: Eagle et al ILASS 2014

Flow analysis @ECN2 MOTIVATION Large scattering in modelling results Boundary conditions? No analysis of velocity/reactive penetration data

MOTIVATION Reacting spray tip penetration Detailed knowledge on the transient dynamics of a reacting jet from high-speed schlieren imaging Mixture shifts from inert to reacting within a transient flow, so there are deviations compared to the well-known inert spray evolution How do tip penetration and radial dispersion evolve with time?

MOTIVATION Reacting spray tip penetration Acceleration of the reacting vs inert spray in terms of the Sr/Si ratio defines some stages in spray tip evolution Autoignition small ‘bump’ in the curve followed by a stabilization period Acceleration compared to the inert case Quasi-steady: Penetration speed is amplified in a constant factor compared to the inert case SOC window limit window limit Ref: Payri et al Applied Thermal Engineering 2015

MOTIVATION Radial dilation vs flame structure Radial expansion as detected by schlieren starts at around the OH* LOL Significant increase in spray width is observed for Spray A conditions R Inert Quasi-steady Transient Ref: Payri et al Applied Thermal Engineering 2015

OBJECTIVES Further investigation on the flow characteristics under reacting conditions PIV field analyis Comparison vs inert evolution Assessment of the capability of CFD models to reproduced the flow characteristics Reacting spray penetration Velocity field

MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS CONTENTS MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS EXPERIMENTS VS CALCULATION Inert flow Reacting flow – Nominal spray A Reacting flow – Low reactivity cases CONCLUSIONS

EXPERIMENTAL ANALYSIS Conditions Experimental information from IFPEN databases PIV LIF (ECN3) Schlieren reacting tip penetration from ECN3 CONDITION Ta [K] rhoa [kg/m3] XO2 [%] Pinj [bar] InjDuration [ms] SA 900 22.8 15/0 1500 1.5 T2 800 7.3 EX 780 14.8 5.0

DESCRIPTION OF REACTING FLOW NOMINAL Spray A PIV derived data

DESCRIPTION OF REACTING FLOW NOMINAL Spray A Evidences of: Increased spray tip penetration Flow acceleration Radial dilation

DESCRIPTION OF REACTING FLOW NOMINAL Spray A Evidences of: Radial dilation Flow acceleration Radial dilation

DESCRIPTION OF REACTING FLOW T2/EX Longer ID/LOL Flow before/after LOL Increased radial expansion

DESCRIPTION OF REACTING FLOW Radial dilation Radial dilation in the velocity field is found downstream of LOL, i.e. high temperature zone SA OH/355 LIF Ru,reac Ru,inert LOL OH*

DESCRIPTION OF REACTING FLOW Radial dilation Radial dilation in the velocity field is found downstream of LOL, i.e. high temperature zone Dilation increases with lower temperatura and density EX OH/355 LIF Ru,reac Ru,inert LOL OH*

MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS CONTENTS MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS EXPERIMENTS VS CALCULATION Inert flow Reacting flow – Nominal spray A Reacting flow – Low reactivity cases CONCLUSIONS

MODELLING CONTRIBUTIONS   ANL USYD CMT TUE POLIMI ETH Zurich UNSW Code name CONVERGE OpenFOAM (mmcFoam) OpenFoam OpenFOAM OpenFOAM with LibICE STAR-CD 4.20 FLUENT 14.5 TURBULENCE Turbulence model LES RANS Standard k-ε RANS k-ε RANS Realizable k-ε Sub-grid or turbulent scalar transport Dynamic structure Smagorinsky/Sparse-Lagrangian gradient transport SPRAY MODEL Used Lagrangian discrete phase model (Y/N)? Y Equivalent gas jet Y,N Injection Blob, Gas-jet Blob Atomization & Breakup KH-RT None KH-RT (with break-up length) KH-RT (w/wo break-up length), Huh, KH, Reitz-Diwakar, ... KH-RT (without break-up length) Reitz-Diwakar No breakup model Collision NTC collision No O'Rourke No collision Drag Dynamic Standard model standardDragModel (OpenFOAM) Dynamic,… Strokes-Cunningham Evaporation Frossling standardEvaporationModel (OpenFOAM) Spalding Heat Transfer Ranz-Marshall Dispersion Stochastic Stoachastic DRW

MODELLING CONTRIBUTIONS   ANL USYD CMT TUE POLIMI ETH Zurich UNSW Code name CONVERGE OpenFOAM (mmcFoam) OpenFoam OpenFOAM OpenFOAM with LibICE STAR-CD 4.20 FLUENT 14.5 GRID Dimensionality 3D domain, 80x80x80 mm 3D 2D axisymmetric Type Structured AMR unstructured Block structured Block structured Cartesian Cartesian 2D Grid size range (mm) 0.0625 mm to 1mm 0.01 mm to 1 mm 0.5x0.25 min 0.2x0.2 mm max 1x1 mm 0.1 mm - 1.25mm 0.5-2.0 0.15 x 0.42mm to 4x11mm Total grid number (#cells) 2.00E+07 6.36E+05 4.67E+04 2.33E+04 2.30E+04 1.60E+04 9.54E+03 TIME ADVANCEMENT Time discretisation scheme PISO Implicit PIMPLE SIMPLE Time-step (sec) Variable with max Courant number equal to 0.75 variable with max Courant No equal to 0.5 1.E-07 1.E-06 4.E-06 Identical injection rate/boundary conditions for all institutions Details on combustion model/chemical mechanisms in the following sections

NOMENCLATURE FOR PIV ANALYSIS Width Same methodology for both PIV and CFD Normalization to accomodate for nozzle differences (675 vs 678) ucl Area R5% 0.05ucl Area~Vdot= 0 𝑅 𝑢∗2𝜋𝑟 𝑑𝑟 Peak value

ETH > TUE-UNSW > CMT-Polimi INERT CASES Spray tip penetration Overall good agreement UNSW deviations in the early penetration zone ETH deviations during the whole time period ETH > TUE-UNSW > CMT-Polimi

INERT CASES Flow variables Overall good agreement ETH/UNSW highest differences in volumetric flow time = 1500 us

MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS CONTENTS MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS EXPERIMENTS VS CALCULATION Inert flow Reacting flow – Nominal spray A Reacting flow – Low reactivity cases CONCLUSIONS

REACTING SPRAY A Sr/Si as derived from CFD General features of the reacting flow are reproduced CMT/Polimi/TUE combustion models produce essentially a quantitatively similar effect on the inert flow UNSW, ETH slower reaction to onse of heat release CMT Polimi TUE UNSW ETH

The inert field does have an influence on reacting flow evolution! REACTING SPRAY A Rective penetration Results are stratified according to inert spray penetration TUe above Polimi-CMT ETH comes together to UNSW The inert field does have an influence on reacting flow evolution! For all cases, si = experiment TUE Polimi CMT ETH-UNSW

REACTING SPRAY A TUE Overpredicted velocity on axis and integral time = 1500 us EXP-REACT EXP-INERT

REACTING SPRAY A CMT/Polimi Good overall agreement time = 1500 us EXP-REACT EXP-INERT

REACTING SPRAY A ETH Good description of the flow under reacting conditions Very high expansion in the Inert-to-reacting transition time = 1500 us EXP-REACT EXP-INERT

REACTING SPRAY A UNSW ETH/UNSW very different flow, same penetration High radial expansion time = 1500 us ETH/UNSW very different flow, same penetration EXP-REACT EXP-INERT

MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS CONTENTS MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS EXPERIMENTS VS CALCULATION Inert flow Reacting flow – Nominal spray A Reacting flow – Low reactivity cases CONCLUSIONS

LOW REACTIVITY CASES Consistency of experimental data T2 ID(ms) LOL(mm) T2 IFPEN (schlieren) ECN3 (chemilum) 0.77 ± 0.06 0.95 24.6 27.5 EX 1.19 ± 0.18 39.5

LOW REACTIVITY CASES Reacting penetration Reasonable agreement of modelling results T2 EX

LOW REACTIVITY CASES T2 case Overall good agreement Polimi lower reactivity, resulting in longer LOL/ID TUE: At a late time instant, no indication of radial dilation time = 4500 us EXP-REACT EXP-INERT

MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS CONTENTS MOTIVATION AND OBJECTIVES EXPERIMENTAL ANALYSIS EXPERIMENTS VS CALCULATION Inert flow Reacting flow – Nominal spray A Reacting flow – Low reactivity cases CONCLUSIONS

EXPERIMENTS CFD CONCLUSIONS Quantification of combustion-induced flow changes Low reactivity cases: Inert to reacting transition in velocity can be quantified Extended flame CFD Accuracy highly improved compared to ECN3 Inert spray evolution has an influence on the reacting case Not a single model predicts penetration/flow characteristics under both inert and reacting conditions

Backup slides

DESCRIPTION OF REACTING FLOW EX Longest ID/LOL Flow before/after LOL Radial expansion ~T2

Dirty laundry…. Data consistency

INERT CASES Spray tip penetration Overall good agreement UNSW deviations in the early penetration zone ETH deviations during the whole time period Momentum flux plot to clarify penetration trend TUE-UNSW > CMT-Polimi time = 1500 us

REACTING SPRAY A ETH Good description of the flow under reacting conditions Inert-to-reacting transition? Much higher radial expansion compared to experiments/other CFD time = 1500 us Polimi

Sensitivity to TCI / Chemistry REACTING SPRAY A Sensitivity to TCI / Chemistry TCI affects ignition timing/LOL, but not subsequent reacting flow dynamics For WM models, Chemistry does have an effect on flow evolution

Sensitivity to TCI / Chemistry REACTING SPRAY A Sensitivity to TCI / Chemistry TCI affects ignition timing/LOL, but not subsequent reacting flow dynamics Chemical mechanism for WM models, strong effect on flow evolution

REACTING SPRAY A Sensitivity to TCI / Chemistry Later ID/LOL higher flow expansion due to autoignition progressing different spatially Later autoignition  higher radial dilation, which is observed experimentally!!

LOW REACTIVITY CASES T2 case Similar overall flow Lower reactivity of Polimi vs TUE  longer LOL/ID EXP-REACT EXP-INERT

LOW REACTIVITY CASES EX case Overall good agreement Polimi too long transition to reacting conditions time = 4300 us EXP-REACT EXP-INERT

Correlation between Mdot stablishment and end of acceleration??

SPRAY A ANALYSIS LOW REACTIVITY CASES CONCLUSIONS CMT/Polimi/TUE Good flow description of flow Reacting tip overprediction TUE overprediction was already happening for the inert case ETH/UNSW good sr prediction Very high radial dilation compared to the inert case LOW REACTIVITY CASES Polimi calculations predict a too long LOL/transition to reaction TUE does better, but radial dilation is not adequately quantified