ECN 3: Combustion Indicator- Experiment and Modeling 1/85 April 2014 ECN 3 Subtopic 2.1: Combustion Indicators Experiment and Modeling 3rd Workshop of the Engine Combustion Network April 4-5, 2014, Ann Arbor, USA Gianluca D’Errico, Seong-Young Lee, Michele Bardi, Jose M. Garcia-Oliver

ECN 3: Combustion Indicator- Experiment and Modeling 2/85 April 2014 Topic 2.1 Combustion Indicator- OUTLINE 1.Introduction of Combustion Indicator o Objectives and Questions to be Addressed 2.Experimental Part o Institutions, Techniques and Operating Conditions 3.Comparison for Global Indicators of Experiment vs. Experiment o Standard measurement for LOL, ID to confirm trend variation o LOL from OH-PLIF comparison o New measurement- FL, Sr, peak concentration in OH-PLIF image 4.Modeling Part o Institutions, models and operating conditions 5.Comparison for Global Indicator of Model vs. Model o Parameters: ID, LOL, FL, Sr, maxOH, maxCH2O: more detail from groups 6.Comparison of Model vs. Experiment in Quantitative Data o Experimental data with modeling data from various groups 7.Comparison of Model vs. Experiment in Time Resolved Data o Heat Release Rate and Flame Tip Srt 8.Conclusion Remarks o Future work and Information for upload data and data availability

ECN 3: Combustion Indicator- Experiment and Modeling 3/85 April 2014 Objectives/ Questions to be Answered OVERALL OBJECTIVES Analyze model and experimental results to determine different parameters that can serve for a global description of the combustion process, namely: Ignition Delay Lift-off Length Reactive Spray Penetration Heat Release Rate OVERARCHING QUESTIONS TO BE ADDRESSED What is the measured and computed dependency of the main “combustion indicators” on the recommended parametric variations of the operating conditions? What are the differences among experiments, among models and between models and experiments? What are the reasons for these differences? What is the influence of the chemical mechanism? What is the influence of the turbulence-chemistry interaction?

ECN 3: Combustion Indicator- Experiment and Modeling 4/85 April 2014 TECHNIQUES AND INDICATORS New CI Conventional CI

ECN 3: Combustion Indicator- Experiment and Modeling 5/85 April 2014 EXPERIMENT

ECN 3: Combustion Indicator- Experiment and Modeling 6/85 April 2014 PARAMETERIC VARIATIONS Conditions tested (n-dodecane) The institutions used different nozzles: SNL: (d 0 = mm) / -370 (d 0 = mm) CMT: (d 0 = mm) IFPEN: (d 0 = mm) IFPEN: , , TU/e: , -679 (d 0 = mm) Spray AT amb O2O2 ρ amb Inj. Pressure SNLXXXX CMTXXXXX IFPENXXX TU/eXX SNL: 800 – 900 – 1000 – 1100 K CMT : 750 – 800 – 850 – 900 K IFPEN: – K SNL: 13 – 15 – 21% CMT: 13 – 15 – 21% IFPEN: 13 – 15 – 17 – 21% SNL: 7.6 – 15.2 – 22.8 kg/m 3 CMT: 7.6 – 15.2 – 22.8 kg/m 3 CMT: 50 – MPa TU/e: 50 – 100 – 150 MPa IFPEN TU/e CMT SNL

ECN 3: Combustion Indicator- Experiment and Modeling 7/85 April 2014 INDICATOR CONTRIBUTIONS LOLIDFL LOL Sr OH* Time avg OH* Transient Broad band OH* Transient PressureBroadbandOH-PLIFSchlieren SNL X (O) X X CMT (O) X X IFPEN X (O) X (OH-LIF/ OH*) TUe (O) X (O) (O) X (OH- LIF/OH*) X ECN3 (Data from Sandia Web) X: New CI X: Conventional CI 1.Ambient temperature [K]: 900 – 800 – 1000 – Injection pressure [MPa]: 150 – Oxygen concentration [%]: 15 – 21 – 17 – 13 4.Ambient density [kg/m 3 ]: 22.8 – 15.2 – 30.4 – Injector:210677, ,

ECN 3: Combustion Indicator- Experiment and Modeling 8/85 April 2014 COMPARISON BETWEEN INSTITUTIONS AND ANALYSIS Ignition Delay (ID) and Lift-off Length (LOL) Reactive Spray Penetration (Sr) Flame length (FL) Heat Release Rate (HRR)

ECN 3: Combustion Indicator- Experiment and Modeling 9/85 April 2014 τSOC_CL Ignition Delays by T amb at Various Institutions τSOC_P τSOC_CL: strong and non-linear temperature dependency while ID slope decreases with increasing ambient temperature τSOC_P: strong and non-linear temperature dependency All ignition delays tend to converge as the temperature increases except for Sandia data at 1100K due to the different criterion, 0.03 kPa as threshold No significant variation with different institutions and injector models

ECN 3: Combustion Indicator- Experiment and Modeling 10/85 April 2014 T amb Effect on ID and Uncertainty Ignition Delay (All Data)Uncertainty Ignition delays appear collapse single profile while there are scatters at lower ambient temperature, 800K Uncertainty is estimated by the ratio of one-sigma over averaged ignition delay at a fixed ambient temperature Above T amb =900K, uncertainty is approximately below 10% for τSOC_CL while large uncertainty is observed in τSOC_P

ECN 3: Combustion Indicator- Experiment and Modeling 11/85 April 2014 T amb Effect on LOL and Uncertainty Lift-off length (LOL)Uncertainty OH*-LOLs converge one single profile with very low uncertainty, below 10% LOL profile shows non-linear behavior, similar to the ID profile No significant deviation in various institutions and injector models

ECN 3: Combustion Indicator- Experiment and Modeling 12/85 April 2014 LOL Dependency of Ta, O2, Density and P inj All data (ECN3) were compiled to build an empirical relationship to predict LOL variations There is a general good agreement with the literature It will provide a guideline for modeling of spray dynamics abcd SAE Benajes et al. 2013, CMT ECN [150MPa 15% 22.8kg/m 3 ] [150MPa 900K 22.8kg/m 3 ] [150MPa 900K 15%] [900K 15% 22.8kg/m 3 ]

ECN 3: Combustion Indicator- Experiment and Modeling 13/85 April 2014 [150MPa 15% 22.8kg/m 3 ] [150MPa 900K 22.8kg/m 3 ] [150MPa 900K 15%] [900K 15% 22.8kg/m 3 ] τSOC_CL Dependency of Ta, O2, Density and P inj All data (ECN3) were compiled to build an empirical relationship to predict τSOC_CL v ariations There is a general good agreement and It will provide a guideline for prediction of flame ignition abcd ECN

ECN 3: Combustion Indicator- Experiment and Modeling 14/85 April 2014 COMPARISON BETWEEN INSTITUTIONS AND ANALYSIS Ignition Delay (ID) and Lift-off Length (LOL) Reactive Spray Penetration (Sr) Flame length (FL) Heat Release Rate (HRR)

ECN 3: Combustion Indicator- Experiment and Modeling 15/85 April 2014 Reactive Flame Tip Penetration (Sr) There is a general good agreement among the institutions and among various injection duration Range of penetration scattering at fixed time is about 3-4 mm Significantly lower penetration by Tu/e over the injection period Diverging penetration when Sr>80mm. Methodology: Schlieren imaging Institution comparison at Ref condition (Spray A)

ECN 3: Combustion Indicator- Experiment and Modeling 16/85 April 2014 Reactive Flame Tip Penetration (Sr) Methodology: Schlieren imaging Inert and Reactive penetration comparison Reactive and inert penetration at a certain ASOI time after the ignition are diverging The information is not representative of the start of ignition. This information can be useful when modeling spray morphology at reacting conditions The indicator Sr/Si can bring valuable information Ignitionc Desantes et al. Combustion and Flames, 2014

ECN 3: Combustion Indicator- Experiment and Modeling 17/85 April 2014 Reactive Flame Tip Penetration (Sr) Methodology: Schlieren imaging Inert and Reactive penetration This parameter has been obtained at different conditions It provides important guidelines on the spray morphology Important information if we are attempting to model spray chemistry! It give consistent results between different institutions (even when the penetration showed some discrepancies)

ECN 3: Combustion Indicator- Experiment and Modeling 18/85 April 2014 COMPARISON AND ANALYSIS Ignition Delay (ID) and Lift-off Length (LOL) Reactive Spray Penetration (Sr) Flame Length (FL) Heat Release Rate (HRR)

ECN 3: Combustion Indicator- Experiment and Modeling 19/85 April 2014 Flame Length (FL) Methodology: Broadband chem./OH *chem. Soot incandescence radiation penetrates until a certain distance depending on injection pressure conditions This distance is related with spray stoichiometric surface, flame length Flame length is independent of injection pressure CMT Spray A - 21% O2 CMT Spray A - 15% O2 CMT % O 2 /150 MPa Ignition

ECN 3: Combustion Indicator- Experiment and Modeling 20/85 April 2014 SCALING LAWS FOR SPRAY LENGTHS CMTSNLTU/e (OH* chem) FL (mm)98.890>95 Similar measurements from all the institutions

ECN 3: Combustion Indicator- Experiment and Modeling 21/85 April 2014 SCALING LAWS FOR SPRAY LENGTHS

ECN 3: Combustion Indicator- Experiment and Modeling 22/85 April 2014 SCALING LAWS FOR SPRAY LENGTHS

ECN 3: Combustion Indicator- Experiment and Modeling 23/85 April 2014 Flame Length (FL) CMTSNLTU/e (OH* chem) FL (mm)98.890>95 SNL900 K1000K1100K FL90 mm88.5 mm84.6 mm Effect of temperature: flame length decrease at higher ambient temperature Similar measurements from all the institutions

ECN 3: Combustion Indicator- Experiment and Modeling 24/85 April 2014 Important remarks: To the moment the FL determination is based on thresholds that has to be further discussed Important fluctuations are involved in the measurement The long distance needed for the flame to stabilize makes FL measurable only at certain conditions The approach needs further discussion but it shows promising results The relationship between Sr, Si and FL and the related test conditions needs further understanding (new challenges for modelers!) Flame Length (FL)

ECN 3: Combustion Indicator- Experiment and Modeling 25/85 April 2014 COMPARISON AND ANALYSIS Ignition Delay (ID) and Lift-off Length (LOL) Reactive Spray Penetration (Sr) Flame length (FL) Heat Release Rate (HRR)

ECN 3: Combustion Indicator- Experiment and Modeling 26/85 April 2014ECN 3 26/4 Apr 2014 Pressure Trace Constant threshold for ignition delay analysis yields inconsistent results at high ambient temperature due to the effect of “ringing” Shortly after high-T ignition, ringing causes pressure traces to drop below zero. Use of averaged and smoothed trace requires a lower threshold at this ambient temperature to capture correct ignition timing. T amb τ press * τ chemi (>3kPa) (>3kPa) 0.23 (>1.5 kPa) (>3kPa) 0.16 (>1.2kPa) (>3kPa) 0.15 (>1kPa) 0.15 *The pressure shown in parenthesis indicates the threshold used for analysis

ECN 3: Combustion Indicator- Experiment and Modeling 27/85 April 2014 Pressure measurement for ID could give trouble especially when the ID premixed phase is reduced (i.e. short ID). This has been observed at high ambient temperature An adjustable polynomial fitting has been employed to fit raw data by SNL (filtering method developed at ETH) The sensitivity is high until the first peak in pressure, then the following fluctuation are heavily filtered Results are to the smoothed signal from the ensemble average Methodology: narrow range pressure sensor in CV vessel (Lillo et al. SAE ) Pressure Rise and ROHR

ECN 3: Combustion Indicator- Experiment and Modeling 28/85 April 2014 Pressure Rise and ROHR Methodology: narrow range pressure sensor in CV vessel (Lillo et al. SAE ) By obtaining the ROHR by the smoothed curve, we defined the ignition delay as the instant corresponding to the highest peak in the ROHR curve The method still needs to be applied to more test conditions SNL800 K900 K1100 K ID Chem [ms] ID PR [ms] ID ROHR [ms]

ECN 3: Combustion Indicator- Experiment and Modeling 29/85 April 2014 LOL CORRELATION BETWEEN OH* AND OH-LIF TUe (201.02) HS OH* images Schlieren movies at injection pressure of 50/100/150 MPa OH-LIF images Laser beam corrected images at 50/100/150MPa at 1100us and 5000us IFPEN (201.01) OH-LIF images Laser beam corrected images of AR, O1, O3, T2, T3 at 150MPa at 5000us AR: [ K 15% 150MPa] O1: [ K 13% 150MPa] O3: [ K 21% 150MPa] T3: [ K 15% 150MPa] T2: [ K 15% 150MPa] I1: [ K 15% 50MPa] I2: [ K 15% 100MPa] AR: [ K 15% 150MPa]

ECN 3: Combustion Indicator- Experiment and Modeling 30/85 April 2014 Beam corrected OH 18% BGs OH 21% BGs OH 25% BGs OH Max_I= % OHmax 29% BGs OH 36% BGs OH10% OHmax Background Subtraction Effect- TU/e [ K 15% 150MPa]

ECN 3: Combustion Indicator- Experiment and Modeling 31/85 April 2014 SENSITIVITY ANALYSIS of OH-LIF Threshold % of OH Max Intensity with Various Background Subtraction BG Subtraction Imax=55.6 Due to Background Interference Detection of OH Signal Start 4% 13.7 mm 17 mm 18.9 mm 25% Background Subtraction Background subtraction (% of maximum intensity) from raw image and normalization Apply 10% max OH to track the location of threshold from injector tip and define the LOL Note that relatively high noise level after laser beam correction

ECN 3: Combustion Indicator- Experiment and Modeling 32/85 April 2014 Relation between OH* and OH-LIF- TU/e A very good agreement of LOL between OH* and OH-LIF

ECN 3: Combustion Indicator- Experiment and Modeling 33/85 April 2014 Background Subtraction Effect- IFPEN Original OH-LIF 5% BGs OH 13% BGs OH 18% BGs OH Max_I= % OHmax 25% BGs OH 36% BGs OH10% OHmax [ K 15%O2 150MPa]:

ECN 3: Combustion Indicator- Experiment and Modeling 34/85 April % threshold of OH max intensity Sensitivity Analysis of 150MPa OH at 4700us- IFPEN BG Subtraction Imax=4747 [ K 15% 150MPa] LOL variation from 0% to 36 % background subtraction is about 16%

ECN 3: Combustion Indicator- Experiment and Modeling 35/85 April 2014 LOL Comparison of OH-LIF and OH*- IFPEN Background 5% subtraction were applied to all cases considered A very good agreement of LOL between OH* and OH-LIF

ECN 3: Combustion Indicator- Experiment and Modeling 36/85 April 2014 CONCLUSIONS ON EXPERIMENTAL PART The newly established experiment provides the rich database for the predictive model development and serves as the benchmark data for modeling Experimental data including quantitative and time-resolved global indicators are available Uncertainty for LOL and ID o LOL variation shows below 10% over various parametric sweeps o Chem-base ID relatively is reliable that Press-base ID o LOL and ID variations are minimal under various institutions and injector models Heat release rate can be used for the definition of ignition delay LOL-OH-LIF shows fairly good agreement with LOL OH* with limited conditions

ECN 3: Combustion Indicator- Experiment and Modeling 37/85 April 2014 MODELLING

ECN 3: Combustion Indicator- Experiment and Modeling 38/85 April 2014 Objectives/ Questions to be Answered OVERALL OBJECTIVES Analyze model and experimental results to determine different parameters that can serve for a global description of the combustion process, namely: Ignition Delay Lift-off Length Reactive Spray Penetration Heat Release Rate OVERARCHING QUESTIONS TO BE ADDRESSED What is the measured and computed dependency of the main “combustion indicators” on the recommended parametric variations of the operating conditions? What are the differences among experiments, among models and between models and experiments? What are the reasons for these differences? What is the influence of the chemical mechanism? What is the influence of the turbulence-chemistry interaction?

ECN 3: Combustion Indicator- Experiment and Modeling 39/85 April 2014 CONTRIBUTIONS ECN3: topic 2.1 Modelling contributions ANL: Argonne National Laboratories (Som, Pei) ETH: Swiss Federal Institute of Technology in Zurich (Bolla) POLIMI: Politecnico di Milano (D’Errico, Lucchini) TUE: Technische Universiteit Eindhoven University of Technology (Somers) UNSW: The University of New South Wales (Hawkes, Chishty) WISC: University of Wisconsin, ERC (Wang) CONTRIBUTOR2.1 T sweep O2 sweep Pinj sweep Rho sweep ANL (1.5 ms) XXXXXX ETH XXXXXX POLIMI XXXXXXX TUE XXXX X UNSW XXXXX X WISC XXXX X X

ECN 3: Combustion Indicator- Experiment and Modeling 40/85 April 2014 CODE(S)Turbulence model(s)Scalar transport ANLCONVERGE RNG k-  Gradient ETHStarCD RNG k-  Gradient PoliMiOpenFOAM + LibICE k-  Gradient TUEStarCD k-  (high Re) Gradient UNSWFluent k- , with round jet adjustment m0: Gradient m1: Weiner process (i.e. gradient) WISCKIVA-3vr gRNG k-  Gradient Models

ECN 3: Combustion Indicator- Experiment and Modeling 41/85 April 2014 ChemistryTurbulence –chemistry interaction ANL Luo et (111 species)Transient multiple representative interactive flamelets (T-RIF). 1 flamelet every ms, flamelet creation based on fuel mass. ETH Luo et al. (106 species)Conditional Moment Closure. Equations solved for conditional moments of species and temperature as function of mixture fraction, space and time. POLIMI Luo et (111 species)Transient multiple representative interactive flamelets (T-RIF). 1 flamelets every 0.1 ms, flamelet creation based on fuel mass. TUE Narayanaswamy (255 species) Flamelet generated manifolds. Tabulation on mixture fraction and progress variables. Beta PDFs for both. UNSW Pei et al (88 species)Transported PDF method. Lagrangian solution of full joint composition mass density function. Well-mixed for comparison. WISC Wang et al.(106 species)Well-mixed.

ECN 3: Combustion Indicator- Experiment and Modeling 42/85 April 2014 Grid type Grid rangeTime discretisation scheme Time step ANL3D, structured with AMR 0.25 mm - 4mmPISO5e-7s variable with max Courant 0.75 ETH2D axisymmetric0.5 mm mmPISO1e-06s CFD 1e-07 s CMC POLIMI2D axisymmetric0.1 mm - 1mmPIMPLE2.50e-7 s TUE3D, uniform Cartesian, ¼ sector 0.5mm X 0.5mm X 0.25 mm PISO5.0e-6 s UNSW2D, structured0.25 mm - 1mmSIMPLE4e-06 s WISC2D axisymmetric0.5 mm-1.5 mmSIMPLE5e-07 s

ECN 3: Combustion Indicator- Experiment and Modeling 43/85 April 2014 Injection/ Break-up CollisionDrag/ Dispersion Heat transfer/ evaporation ANL Inj: Blob Break-up: KH-RT without breakup length Collision: “no time counter” algorithm Drag: Dynamic model Dispersion: Stochastic HT: Ranz-Marshall Evap: Frossling ETH Inj: Blob Break-up: Reitz-Diwakar O’RourkeDrag: Dynamic Dispersion: Stochastic HT: Ranz-Marshall Evap: Ranz-Marshall POLIMI Inj: Blob Break-up: KH-RT without breakup length NoDrag: Dynamic Dispersion: Stochastic HT: Ranz-Marshall Evap: Spalding TUE Inj: Nozzle flow model - Modified MPI* Break-up: Reitz-Diwakar O’RourkeDrag: Star-CD standard Dispersion: Stochastic HT: Ranz-Marshall Evap: Standard UNSW Inj: Group Break-up: No (inject small droplets) O’RourkeDrag: Stokes-Cunningham Dispersion: stochastic HT: Ranz-Marshall Evap: Frossling WISC Inj: Blob Break-up: KH-RT O’RourkeDrag: Dynamic model Dispersion: none HT: Han and Reitz Evap: Discrete Multi- Component

ECN 3: Combustion Indicator- Experiment and Modeling 44/85 April 2014 Models for turbulence-chemistry interaction Well-mixed (UNSW, WISC): – Mixing is fast relative to chemistry. – Fast mixing causes the scalar PDFs to be close to  -functions. Presumed PDF/flamelet approaches (ANL, POLIMI, TUE): – The thermochemical state-space is low-dimensional and described by a few parameters. – The forms of the parameter PDFs are known and described by a small number of moments usually two, e.g. beta functions, Gaussian or one, e.g. delta function. – There is some way of obtaining thermochemical state conditional on the parameters.

ECN 3: Combustion Indicator- Experiment and Modeling 45/85 April 2014 Models for turbulence-chemistry interaction Presumed PDF/flamelets (ANL, POLIMI, TUE): Chemistry is fast relative to mixing. Ignition of a one-dimensional laminar non-premixed stagnation flow. (Or an approximation to this.) Different table parameter choices possible. TUe - mixture fraction and progress variables. Beta PDFs for both. ANL, POLIMI – transient multiple representative interacting flamelet with a beta PDF. Chemistry in online solved in the mixture fraction space. Each flamelet is representative of a fraction of the injected fuel mass. Average stoichiometric scalar dissipation rate values are passed to each flamelet.

ECN 3: Combustion Indicator- Experiment and Modeling 46/85 April 2014 Conditional Moment Closure (ETH) Chemistry Conditional turbulent flux Species Molecular mixing Conditional velocity Models for turbulence-chemistry interaction Equations are solved for species and temperature, conditionally averaged on mixture fraction. Conditional fluctuations are assumed to be small. Mixture fraction PDF is presumed as a beta function. In some respects similar to flamelets but the “tabulation” evolves in time and space. (In space, on a coarser grid than the CFD.)

ECN 3: Combustion Indicator- Experiment and Modeling 47/85 April 2014 Models for turbulence-chemistry interaction Transported PDF approaches (UNSW)

ECN 3: Combustion Indicator- Experiment and Modeling 48/85 April 2014 Comparison among used kinetic mechanisms Constant volume homogeneous ignitions were modelled using SENKIN. Ignition was defined computationally as the time of the maximum rate of change of temperature. The following three chemical mechanisms were compared: - Narayanaswamy et al.: a 255 species mechanism. -Som et al.: 111 species skeletal mechanism (based on Luo et al. with the skeletal mechanism for OH* added). -Pei et al.: an 88 species reduced mechanism (quasi-steady state assumptions to the 111 species mechanism). The model was compared with ignition delays from shock tubes: o Pfahl et al. : n-decane, pressure = 50 bar, phi = 0.67, 1.0 and 2.0 o Zhukuv et al. : n-decane, pressure = 80 bar, phi = 1.0 o Vasu et al. : n-dodecane, pressure = 20 bar, phi =1.0. (The raw data were scaled to 20 bar) Separately Wang provided information on the validation of 106 species mechanism formulated at UW-ERC, showing good agreement with Narayanaswamy et al, especially at high temperatures. Chemical mechanisms

ECN 3: Combustion Indicator- Experiment and Modeling 49/85 April 2014 Chemical mechanisms Comparison among used kinetic mechanisms Results from Som et al. and Pei et al. are nearly identical. The Som et al. mechanism and the Narayanaswamy et al. do not significantly differ at low temperatures. The main difference is in the high temperature range. For 50 bar or higher pressure, at temperatures below ~900K the mechanisms all over- predict the ignition delay, and there is little to distinguish between the mechanisms. This is significant because the spray A baseline ignites at a phi > 2.0 where the temperature is under 850K. Narayanaswamy et al. mechanism mainly improves the high temperature behaviour relative to the starting detailed mechanism of Som et al.

ECN 3: Combustion Indicator- Experiment and Modeling 50/85 April 2014 Modelling definitions

ECN 3: Combustion Indicator- Experiment and Modeling 51/85 April 2014 Models for turbulence-chemistry interaction Parametric variations Models vs Experiments First Ignition Delay/LOL analyis is shown for: 1. Ambient Temperature [K]: 900 – 800 – 1000 – Injection pressure [MPa]: 150 – Oxygen concentration [%]: 15 – 21 – 17 – Ambient density [kg/m 3 ]: 22.8 – 15.2 – 30.4 – 7.6 For each operating point, one value of experimental data is reported with the observed scatter of data among different institutions.

ECN 3: Combustion Indicator- Experiment and Modeling 52/85 April 2014 Ignition delay/LOL Temperature sweep For the experimental data, a mean value for each operating condition is shown with a scatter bar of all data collected at different institutions. All models over-predict the ignition delay, while LOL is generally better estimated. Computed and experimental trends are generally in good agreement.

ECN 3: Combustion Indicator- Experiment and Modeling 53/85 April 2014 Ignition delay/LOL Results do not explicitly depend on the chemical scheme ETH and TUE have a lower ID for the baseline condition, but this is not confirmed for other operating conditions. POLIMI and UNSW have a similar trend and values. ANL has globally the lower ID for all conditions. Temperature sweep (ID) The over-prediction of ID by all groups is consistent with the chemistry sub-models over- predicting the ignition delay at high pressures and temperatures less than around 900K. Models show that the ignition shifts to richer (and thus cooler) regions as ambient temperature is increased, such that the ignition still occurs at a temperature less than 900K. This effect is due to the NTC.

ECN 3: Combustion Indicator- Experiment and Modeling 54/85 April 2014 Ignition delay/LOL Overall trends are good, but differences among models are significant. POLIMI and UNSW have generally the closer values to the measured data. Most relevant errors are WISC at 900 K, ANL at 800 K and TUE at 1100 K… not a unique “worse” condition! Absolute values might depend on the definition Temperature sweep (LOL)

ECN 3: Combustion Indicator- Experiment and Modeling 55/85 April 2014 Ignition delay/LOL Higher Error in the prediction of the ignition delay than of the lift-off length (chemistry?) There is no evident correlation between the two combustion indicators in any of the models.

ECN 3: Combustion Indicator- Experiment and Modeling 56/85 April 2014 Ignition delay/LOL Do the conclusions depend on the ID definition? ETH and TUE provided results with both definitions: - OH mass fraction: First time at which Favre-average OH mass fraction reaches 2% of the maximum in the domain after a stable flame is established. -Temperature rise: Time of maximum rate of rise of maximum temperature Results are the same with both definitions.

ECN 3: Combustion Indicator- Experiment and Modeling 57/85 April 2014 Ignition delay/LOL Do the conclusions depend on the LOL definition? ANL and UNSW provided results with two definitions (2% and 14% of max OH). Computed trends are similar with an obvious shift towards higher values with the 14% maxOH definition. This difference is more significant for ANL results than UNSW.

ECN 3: Combustion Indicator- Experiment and Modeling 58/85 April 2014 Is it possible to use a LOL definition based on OH*? Ignition delay/LOL POLIMI - AR OH OH* Trend seems to captured despite the very low values. A different threshold would be needed to be consistent with the OH based definition.

ECN 3: Combustion Indicator- Experiment and Modeling 59/85 April 2014 Ignition delay/LOL What about turbulence-chemistry interactions? Only UNSW provided results with both TCI (Tpdf) and well-mixed approach, while WISC provided results only with well-mixed. Ignition delay (UNSW) does not depend significantly on TCI. In literature and at ECN2 some groups had shown opposite conclusions. UNSW well-mixed results are different from WISC. LOL with the well-mixed approaches for WISC and UNSW are closer.

ECN 3: Combustion Indicator- Experiment and Modeling 60/85 April 2014 Ambient oxygen sweep Ignition delay/LOL Ignition delay Overall over-estimation is confirmed. ANL and POLIMI (both mRIF) have similar trends (and values). UNSW and TUE have similar trends (not values).

ECN 3: Combustion Indicator- Experiment and Modeling 61/85 April 2014 Ambient oxygen sweep Ignition delay/LOL Lift-off Overall good prediction also quantitative (apart from WISC with well-mixed approach). ETH, POLIMI and UNSW have similar trends in good agreement with the experimental values.

ECN 3: Combustion Indicator- Experiment and Modeling 62/85 April 2014 Other indicator Position of maximum OH and CH2O Apart from the 800 K (where some results might not be stable yet): -POLIMI and UNSW have similar locations of OH and CH2O, either as trends and as absolute values. - TUE predicts a longer distance between OH and CH2O. -ETH results predicts very close locations for the AR case.

ECN 3: Combustion Indicator- Experiment and Modeling 63/85 April 2014 Ignition delay/LOL What about turbulence-chemistry interactions now? Some differences arise in the ignition delay (UNSW) for the oxygen sweep. LOL with the well-mixed approaches for WISC and UNSW are closer for the oxygen sweep too.

ECN 3: Combustion Indicator- Experiment and Modeling 64/85 April 2014 Ambient density sweep Ignition delay/LOL Ignition delay and Lift-off All models show similar trends for ID and LOL as function of ambient density.

ECN 3: Combustion Indicator- Experiment and Modeling 65/85 April 2014 Fuel injection pressure sweep Ignition delay/LOL Ignition delay and Lift-off have opposite trend as function of the injection pressure Some results (ANL, ETH, POLIMI, TUE) capture (with different degree of accuracy) both trends. Very interesting conditions to understand the flame stabilization mechanisms.

ECN 3: Combustion Indicator- Experiment and Modeling 66/85 April 2014 Other indicators Reactive spray penetration: temperature sweep Experimental reactive spray penetration were compared at 1.5 ms with the modelling results. Absolute values depend on the capability of the model to well describe the transient evolution of the flame. For this aspect, the good set-up of the spray model has a great influence too. Some institutions provided time resolved data which can help to understand the differences, as we will see later.

ECN 3: Combustion Indicator- Experiment and Modeling 67/85 April 2014 Other indicators Reactive spray penetration: oxygen sweep This sweep is very interesting for RSP data since it is done at constant thermodynamic conditions. POLIMI and WISC results are in good agreement with the measured data. Other models show a weak dependency of the RSP on the oxygen concentration.

ECN 3: Combustion Indicator- Experiment and Modeling 68/85 April 2014 Other indicators Reactive spray penetration: ambient density sweep All models are able to well capture the dependency of the RSP on the ambient density as trend.

ECN 3: Combustion Indicator- Experiment and Modeling 69/85 April 2014 Other indicators Reactive spray penetration: fuel injection pressure sweep ANL results have an opposite trend with the injection pressure. All other models well predict this dependency with particularly good agreement for POLIMI and WISC.

ECN 3: Combustion Indicator- Experiment and Modeling 70/85 April 2014 Other indicators: time-resolved Reactive spray penetration: reacting baseline (AR) The time-resolved RSP data helps in understanding the observed differences among models. In the baseline case, the differences due to the spray model set-up are particularly evident.

ECN 3: Combustion Indicator- Experiment and Modeling 71/85 April 2014 Other indicators: time-resolved Reactive spray penetration: reacting vs non-reacting For two models, it was possible to compare the Spray penetration computed in the non-reacting (topic 1.2) and reacting cases under the same thermodynamic conditions. POLIMI results are in good agreement with the measured data.

ECN 3: Combustion Indicator- Experiment and Modeling 72/85 April 2014 Heat release rate Other indicators: time-resolved Comparison for the baseline reacting case (AR) ETH, POLIMI and WISC have a similar “steady” value of HRR, which is lower (why?) than the measured data. UNSW has an increase of HRR after 2 ms (numerical issues with the pdf method?) Models with TCI have a similar description of the initial stages of combustion (cool flame, premixed, mixing-controlled).

ECN 3: Combustion Indicator- Experiment and Modeling 73/85 April 2014 Heat release rate Other indicators: time-resolved

ECN 3: Combustion Indicator- Experiment and Modeling 74/85 April 2014 Time-resolved Conclusions on the modelling part (#1) GLOBAL INDICATORS The available experimental database allows an extended validation of the model capability to well predict ignition delay and lift-off length. Generally all models tend to over-estimate the ID for all conditions. -Need more shock tube and flow reactor data in spray A relevant conditions to improve current kinetic mechanisms. -Current chemical mechanism give comparable results when applied to Spray A conditions. Models with TCI showed a good capability of predicting LOL absolute values and trends. Well-mixed approaches can capture the qualitative trend.

ECN 3: Combustion Indicator- Experiment and Modeling 75/85 April 2014 Time-resolved Conclusions on the modelling part (#2) TIME RESOLVED RESULTS Time resolved spray penetrations computed by all groups differ significantly. Models need to be well set-up under non reacting conditions first to well capture the transient behavior the flame. If properly set-up, model can capture the effect of the reactions on the spray penetration evolution. The comparison of heat release rate between models and experiments, showed some discrepancies not only in the ignition prediction but also in the “steady state” rate of combustion. More investigation is required.

ECN 3: Combustion Indicator- Experiment and Modeling 76/85 April 2014 BACK-UP SLIDE

ECN 3: Combustion Indicator- Experiment and Modeling 77/85 April 2014 IFPEN TUe OH*OH-LIF HS-OH*OH-LIF Fueln-dodecane Injector Injection pressure1500 bar 500/1000/1500 bar Injection duration 5 ms Laser-Q1(6): nm -Q1(9): nm Energy mJ/pulse -11 mJ/pulse Laser sheet length (width)-20 mm (<0.5mm) -30 mm Laser timing ACOI5.0 ms 5.0 ms + 3 µ s -5.0 ms – 1.1 ms Filters315 nm (15nm) 307 nm (5nm)315 nm (15nm) CameraPIMAX2-ICCD Lambert Hi-CAMPIMAX3-ICCD Exposure duration2.5 ms50 ns µ s 50 ns Ensemble averaged10 10 (5 at 1 &1.1 ms) Spatial resolution~0.1mm/pixel ~0.2mm/pixel~0.03mm/pixel IFPEN and TUe Conditions

ECN 3: Combustion Indicator- Experiment and Modeling 78/85 April 2014 OH* OH-LIF OH-OH* Overlap OH-Intensity 10% OHmax Visual Inspection (OH-LIF at 5 ms vs OH* at 4.2ms) By Definition (10% max OH-LIF)- No Background Subtraction Overlay of OH-LIF and OH* at 150 MPa- TUe

ECN 3: Combustion Indicator- Experiment and Modeling 79/85 April 2014 Background Subtraction Effect- IFPEN Original OH-LIF 5% BGs OH 13% BGs OH 18% BGs OH Max_I= % OHmax 25% BGs OH 36% BGs OH10% OHmax [ K 15%O2 150MPa]:

ECN 3: Combustion Indicator- Experiment and Modeling 80/85 April 2014 Beam corrected OH 18% BGs OH 21% BGs OH 25% BGs OH Max_I= % OHmax 29% BGs OH 36% BGs OH10% OHmax Background Subtraction Effect- TU/e [ K 15% 150MPa]

ECN 3: Combustion Indicator- Experiment and Modeling 81/85 April 2014 Oxygen Effect on ID τSOC_CLτSOC_P τSOC_CL: linear dependency with oxygen level except IFPEN (201.01) at 13% O2 level and largely scatters at high O2 level τSOC_P: linear dependency with oxygen No significant variation in different institutes and injector models but data scatter increases with increasing O2 level

ECN 3: Combustion Indicator- Experiment and Modeling 82/85 April 2014 Ignition Delay (All Data)Uncertainty Oxygen Effect on ID and Uncertainty Ignition delays appear linear profile with increasing O2 level while τSOC_CL shows slightly longer that τSOC_P at fixed O2 level For all O2 level considered, uncertainty is approximately below 10% for τSOC_P while τSOC_CL shows slightly higher uncertainty

ECN 3: Combustion Indicator- Experiment and Modeling 83/85 April 2014 Uncertainty Oxygen Effect on LOL and Uncertainty Lift-off length (LOL) decreases with increasing O2 level while slightly more scatters are observed at a given O2 level For all O2 level considered, uncertainty is approximately below10% and increase trend with O2 level Lift-off length (LOL)

ECN 3: Combustion Indicator- Experiment and Modeling 84/85 April 2014 Amb Density Effect on ID and LOL Ignition DelayLift-off length (LOL)

ECN 3: Combustion Indicator- Experiment and Modeling 85/85 April 2014 Injection Pressure Effect on ID and LOL IDLOL