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Bridging the gap: How Spray details (Topic 1) affect Combustion (Topic 2)Yuanjiang Pei, Sibendu Som: Argonne National LaboratoryJose Garcia: CMT-Motores Termicos4/5/2014ObjectivesDesigned to bridge-the-gap between spray (Topic 1) and combustion (Topic 2) for Spray AHow do the differences in the initial boundary conditions and spray characteristics influence combustion characteristics?Can simulations using the best boundary conditions available, capture these trends?Why differences in spray characteristics do not seem to influence the combustion behavior?What are the most sensitive variables for different targets of spray and combustion characteristics? - (global sensitivity analysis)

ECNMOTIVATION

A comparison between an inert spray and a reacting one seems to be pertinentInsight into the analysis of flame time evolutionValidation of modelling

Modelling results will be shown to enable the potential of such a comparisonNominal Spray A under inert (0% O2) and reacting (15% O2) conditionsETH CFD results (few available calculations for both inert and reacting conditions)

INERT VS REACTING SPRAYECN

INERT VS REACTING SPRAYOn-axis cl valuesRadial integralECN

PENETRATIONRADIUSFLUXON-AXISINERT VS REACTING SPRAYLAYOUTECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYBefore SOC Similar spray behaviourECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYAfter SOC Radial expansion of the sprayECNECN 3 Bridge the gap#April 5th 2014

Radius, Little effect on tip penetrationmdot (entrainment)Mdot unbalancedMdot = =M0nozzleucl, zclINERT VS REACTING SPRAYAfter SOC Radial expansion of the sprayECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYAfter SOC Radial expansion of the sprayECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYAcceleration of reacting tip over inert oneucl, zclECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYAcceleration of reacting tip over inert oneECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYAcceleration of reacting tip over inert oneECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYAcceleration of reacting tip over inert oneECNECN 3 Bridge the gap#April 5th 2014

Mdot = Mdot = =M0nozzleINERT VS REACTING SPRAYQuasi-steady penetrationmdot (entrainment)ECNECN 3 Bridge the gap#April 5th 2014

INERT VS REACTING SPRAYQuasi-steady penetrationECNECN 3 Bridge the gap#April 5th 2014

Stabilized Flame length??INERT VS REACTING SPRAYQuasi-steady penetrationucl, zclmdot (entrainment)Mdot = Mdot = =M0nozzleRadius ECNECN 3 Bridge the gap#April 5th 2014INERT VS REACTING SPRAYSequence of eventsInitial identical penetrationHeat release induces radial expansionFlow rearranges internally and undergoes an acceleration period as a quasi-steady flowSame momentumLower entrainmentHigher velocities

ECNECN 3 Bridge the gap#April 5th 2014Recent investigations of nozzle to nozzle variationsECN2 showed similar ignition delay and lift-off length measurements among different facilities despite the variations of (ECN2 proceedings: Ignition andLift-off Length, 2012):InjectorsAmbient compositions, e.g., CVP vs. CPFMeasurement techniquesDispersionLiquid length17%Vapor penetration length5% at 1 msIgnition delayLess than 5%Lift-off length7%A set of new Spray A injectors investigated at IFPEN (Malbec et al. SAE Paper 2013-24-0037):Significant difference on liquid lengthMuch smaller dispersion of the results in the far fieldECNRecap ECN2 and a recent study at IFPEN. Motivation of the study in this session.18Why differences in spray characteristics do not seem to influence the combustion behavior?---- Momentum driven!Questions to answer:Global Sensitivity AnalysisWhat are the most sensitive boundary conditions and variables affecting different spray and combustion targets?ECNKey Steps For GSASimulations varying all variables over uncertainty ranges simultaneouslyFit the response (ignition delay, liquid length, etc) to the uncertainties20The fit of the response to the uncertainties leads to a variance associated with each variable (partial variance: Vi)Calculate sensitivity coeffs., Si = Vi/V, Si 1, (V: total variance)

Y. Pei, R. Shan, S. Som, T. Lu, D. Longman, M.J. Davis, SAE Paper 2014-01-1117, 2014.D.Y. Zhou, M.J. Davis, R.T. Skodje, The Journal of Physical Chemistry A, pp. 3569-3584, 2013.ECNVariables and their Uncertainty RangeParametersMinMaxBoundariesVessel wall temperature (K)400800Initial gas velocity fluctuation (m/s)0.011Ambient temperature (K)887.5915.1Ambient pressure (MPa)5.916.09Ambient O214.915.1OH (ppb)016CO206.4H2O011.6Duration of injection (ms)1.491.65Fuel temperature (K)343403Discharge coefficient0.880.92Nozzle diameter (micron)83.790.8Fuel propertiesCritical temp (K)645659Density*0.981.02Heat of vopoization*0.981.02Vapor pressure*0.981.02Viscosity*0.981.02* Normalized by the baseline valuesMaybe even bigger!!Targets studied:Liquid lengthVapor penetration length at 1.5 msIgnition delayLift-off length

An example of liquid length results from 60 casesECN

WM: 60 cases x 250 cpu hoursRIF: 120 cases x 1000 cpu hoursLift-off length vs. ignition delay Clear correlation between lift-off length and ignition delay:Longer ignition delay -> longer lift-off lengthExpe: 900 KECN

Ignition delay and lift-off length vs. liquid lengthNo correlation was found for all the ambient conditions:Ignition delay vs. liquid lengthLift-off length vs. liquid lengthECNUncertainty Quantification Liquid lengthLiquid length at 900 K:Fuel temperature dominates liquid lengthsTrend predicted well compared with Pickett et al. 2010-01-2106 Meijer et al. AAS - 6083Ambient T is not picked up probably due to the large uncertainty of the fuel T.

Pickett et al.2010-01-2106ECNUncertainty Quantification Liquid lengthLiquid length:Fuel temperature dominates liquid lengths at 800 K and 1100 K.Nozzle diameter becomes important for 1100 K condition, probably due to the faster vaporization rate.ECNUncertainty Quantification Vapor penetration length

Nozzle diameter ranks #1 for vapor penetration length at 900 K.Similar for 800 K and 1100 K conditions.Different nozzles showed 5% dispersion in Malbec et al SAE 2013-24-0037. 900 KECNUncertainty Quantification ID800 K800 K:Ambient T dominatesAmbient O2 doesnt show up

1100 K:Ambient T rank #1Comparable OH and ambient O21100 K

[Pickett et al. SAE 2005-01-3843]ECN27Uncertainty Quantification ID

900 KAmbient O2 dominates at 900 K.Ambient T is not sensitive around 900 K, probably due to NTC behavior?

[Pickett et al. SAE 2005-01-3843]ECNUncertainty Quantification LOL

900 KAmbient O2 dominates at 900 K.Comparable sensitivity of nozzle diameter:Bigger nozzle diameter, longer lift-off length.

In agreement with Siebers and Higgins, SAE Paper, 2001-01-0530.ECNUncertainty Quantification LOL800 K1100 K800 K:Ambient T dominatesComparable OH and nozzle diameter

1100 K:Ambient T is most sensitiveComparable ambient O2 and nozzle diameter[Siebers et al. SAE 2002-01-0890]

ECNClear correlation of ignition delay and lift-off length. No clear relation for ignition delay and lift-off length vs. liquid length.Fuel temperature is clearly important for liquid length.Ignition delay and lift-off length:Ambient composition and ambient temperature play significant roles.Even though fuel temperature uncertainty is so big, it does not seem to significantly affect ignition delay and lift-off length.Nozzle diameter seems to affect vapor penetration and lift-off length.

Summary and Conclusions:ECNHow do the differences in the initial boundary conditions and spray characteristics influence combustion characteristics?Can simulations using the best boundary conditions available?Questions to answer:ECNTemperature distribution in the vesselExperiments:Meijer et al., AAS, 2012ECN websiteTemperature distribution in the vessels due to buoyancySmall on spray axis after 4 mmSmall on horizontal planeSignificant on vertical directionThe near injector region, courtesy of Lyle Pickett.

Especially in the region < 2 mm, close the injectorvacuum cleaner

ECNDilatation and entrainment effect

Temporal evolution of dilation effect of reacting condition compared to the nonreacting condition at Tamb = 900 K. The black solid line is the reacting boundary.The green dash-dot line is the non-reacting boundary. The red dashed line is flame existing.The blue arrows are the ambient velocity vectors.Non-reacting case:(Vectors show the expected features of a transient jet)Axial velocities peak on the centre lineA radially diverging flow around the jet head.Entrainment is evident towards the nozzle. Combination of the radially diverging flow at the head and the entrainment flow behind creates a counter-clockwise vortex.Observed in experimental PIV measurements of the same case at IFPEN (ECN2 proceedings, 2012).

Reacting case:(Similar flow structure)Significant dilatation due to combustion, e.g., at 1.0 ms, strong outwardly expanding flow due to intense premixed burn.Couples with the entraining flow to create an even stronger counter clockwise vortex.Transport of hot products upstream of the flame base, accelerating ignition and promoting flame stabilisation further downstream.Y. Pei, PhD thesis, UNSW, 2013ECN

T ratio 900 K initializationInjector protrudes into vessel 1.1 mm.Smallest cell size 0.125 mm.Good initialization compared to measurements on the injector centerline.

Injector

Injector starts hereECN

T difference in the core region can be as high as 100 K, or even more!T profilesAt X = 2 mm, ambient T is lower than initial T indicates that the cold gas near the boundary layer is really pulled in. At X = 10 mm, the hot and cold ambient gas in upper and lower vessel is entrained into mixing layer.Low T reactionECNMovie Uniform T vs. Actual T%900 KLiquid length17.23Ignition delay16.0Lift-off length5.31100 K27.56.08.1Actual T delays ignitionAsymmetric flame found in simulation, but not systematically observed in experiments yet (SAE Paper, 2010-01-2106)

Retarded ignition will make the ignition delay predictions even worse in topic 2!

Better chemical mechanism!!ECNRandom variation in T on top of the mean

No T variationT variation +/- 10 KRandom variation in temperature on top of the mean (+/- 10 K for 900 K case)Pickett et al. SAE 2010-01-2106Three random cases tested:%900 KLiquid length0.8%Ignition delay2.3Lift-off length3.9ECNActual temperature distribution in the combustion vessel is very important.Asymmetric flameSignificantly affect spray and combustionSuggestions:Experiments: temperature distribution in the < 2 mm region should be measured with capable instrumentsSimulations: use this actual temperature distribution.Better chemical mechanism for n-dodecane!!Conclusion and Suggestions:ECNThanks Michal Davis for providing the code of global sensitivity analysis.Thanks Lyle Pickett, Maarten Meijer and Julien Manin for the useful discussions.AcknowledgementECN