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Bridging the gap: How Spray details (Topic 1) affect Combustion (Topic 2) Yuanjiang Pei, Sibendu Som: Argonne National Laboratory Jose Garcia: CMT-Motores Termicos 4/5/2014 Slide 2 Objectives Designed to bridge-the-gap between spray (Topic 1) and combustion (Topic 2) for Spray A How 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) Slide 3 MOTIVATION A comparison between an inert spray and a reacting one seems to be pertinent Insight into the analysis of flame time evolution Validation of modelling Modelling results will be shown to enable the potential of such a comparison Nominal Spray A under inert (0% O2) and reacting (15% O2) conditions ETH CFD results (few available calculations for both inert and reacting conditions) INERT VS REACTING SPRAY Slide 4 On-axis cl values Radial integral Slide 5 ECN 3 Bridge the gap 5 April 5 th 2014 PENETRATION RADIUS FLUXON-AXIS INERT VS REACTING SPRAY LAYOUT Slide 6 ECN 3 Bridge the gap 6 April 5 th 2014 INERT VS REACTING SPRAY Before SOC Similar spray behaviour Slide 7 ECN 3 Bridge the gap 7 April 5 th 2014 INERT VS REACTING SPRAY After SOC Radial expansion of the spray Slide 8 ECN 3 Bridge the gap 8 April 5 th 2014 Radius, Little effect on tip penetration mdot (entrainment) Mdot unbalanced Mdot = =M0nozzle ucl, zcl INERT VS REACTING SPRAY After SOC Radial expansion of the spray Slide 9 ECN 3 Bridge the gap 9 April 5 th 2014 INERT VS REACTING SPRAY After SOC Radial expansion of the spray Slide 10 ECN 3 Bridge the gap 10 April 5 th 2014 INERT VS REACTING SPRAY Acceleration of reacting tip over inert one ucl, zcl Slide 11 ECN 3 Bridge the gap 11 April 5 th 2014 INERT VS REACTING SPRAY Acceleration of reacting tip over inert one Slide 12 ECN 3 Bridge the gap 12 April 5 th 2014 INERT VS REACTING SPRAY Acceleration of reacting tip over inert one Slide 13 ECN 3 Bridge the gap 13 April 5 th 2014 INERT VS REACTING SPRAY Acceleration of reacting tip over inert one Slide 14 ECN 3 Bridge the gap 14 April 5 th 2014 Mdot = Mdot = =M0nozzle INERT VS REACTING SPRAY Quasi-steady penetration mdot (entrainment) Slide 15 ECN 3 Bridge the gap 15 April 5 th 2014 INERT VS REACTING SPRAY Quasi-steady penetration Slide 16 ECN 3 Bridge the gap 16 April 5 th 2014 Stabilized Flame length?? INERT VS REACTING SPRAY Quasi-steady penetration ucl, zcl mdot (entrainment) Mdot = Mdot = =M0nozzle Radius Slide 17 ECN 3 Bridge the gap 17 April 5 th 2014 INERT VS REACTING SPRAY Sequence of events Initial identical penetration Heat release induces radial expansion Flow rearranges internally and undergoes an acceleration period as a quasi-steady flow Same momentum Lower entrainment Higher velocities Slide 18 Recent investigations of nozzle to nozzle variations ECN2 showed similar ignition delay and lift-off length measurements among different facilities despite the variations of ( ECN2 proceedings: Ignition and Lift-off Length, 2012 ): Injectors Ambient compositions, e.g., CVP vs. CPF Measurement techniques Dispersion Liquid length17% Vapor penetration length5% at 1 ms Ignition 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 length Much smaller dispersion of the results in the far field Slide 19 Why differences in spray characteristics do not seem to influence the combustion behavior? ---- Momentum driven! Questions to answer: Global Sensitivity Analysis What are the most sensitive boundary conditions and variables affecting different spray and combustion targets? Slide 20 Key Steps For GSA Simulations varying all variables over uncertainty ranges simultaneously Fit the response (ignition delay, liquid length, etc) to the uncertainties 20 The fit of the response to the uncertainties leads to a variance associated with each variable (partial variance: V i ) Calculate sensitivity coeffs., S i = V i /V, S i 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. Slide 21 Variables and their Uncertainty Range ParametersMinMax BoundariesVessel wall temperature (K)400800 Initial gas velocity fluctuation (m/s)0.011 Ambient temperature (K)887.5915.1 Ambient pressure (MPa)5.916.09 Ambient O214.915.1 OH (ppb)016 CO206.4 H2O011.6 Duration of injection (ms)1.491.65 Fuel temperature (K)343403 Discharge coefficient0.880.92 Nozzle diameter (micron)83.790.8 Fuel propertiesCritical temp (K)645659 Density*0.981.02 Heat of vopoization*0.981.02 Vapor pressure*0.981.02 Viscosity*0.981.02 * Normalized by the baseline values Maybe even bigger!! Targets studied: Liquid length Vapor penetration length at 1.5 ms Ignition delay Lift-off length An example of liquid length results from 60 cases Slide 22 WM: 60 cases x 250 cpu hours RIF: 120 cases x 1000 cpu hours Lift-off length vs. ignition delay Clear correlation between lift-off length and ignition delay: Longer ignition delay -> longer lift-off length Expe: 900 K Slide 23 Ignition delay and lift-off length vs. liquid length No correlation was found for all the ambient conditions: Ignition delay vs. liquid length Lift-off length vs. liquid length Slide 24 Uncertainty Quantification Liquid length Liquid length at 900 K: Fuel temperature dominates liquid lengths Trend predicted well compared with Pickett et al. 2010-01-2106 Meijer et al. AAS - 6083 Ambient T is not picked up probably due to the large uncertainty of the fuel T. Pickett et al. 2010-01-2106 Slide 25 Uncertainty Quantification Liquid length Liquid 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. Slide 26 Uncertainty 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 K Slide 27 Uncertainty Quantification ID 800 K 800 K: Ambient T dominates Ambient O 2 doesnt show up 1100 K: Ambient T rank #1 Comparable OH and ambient O2 1100 K [Pickett et al. SAE 2005-01-3843] Slide 28 Uncertainty Quantification ID 900 K Ambient O 2 dominates at 900 K. Ambient T is not sensitive around 900 K, probably due to NTC behavior? [Pickett et al. SAE 2005-01-3843] Slide 29 Uncertainty Quantification LOL 900 K Ambient O 2 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. Slide 30 Uncertainty Quantification LOL 800 K 1100 K 800 K: Ambient T dominates Comparable OH and nozzle diameter 1100 K: Ambient T is most sensitive Comparable ambient O2 and nozzle diameter [Siebers et al. SAE 2002-01-0890] Slide 31 Clear 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: Slide 32 How 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: Slide 33 Temperature distribution in the vessel Experiments: Meijer et al., AAS, 2012 ECN website Temperature distribution in the vessels due to buoyancy Small on spray axis after 4 mm Small on horizontal plane Significant on vertical direction The near injector region, courtesy of Lyle Pickett. Especially in the region < 2 mm, close the injector vacuum cleaner Slide 34 Dilatation and entrainment effect Temporal evolution of dilation effect of reacting condition compared to the nonreacting condition at T amb = 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 line A 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, 2013 Slide 35 T ratio 900 K initialization Injector protrudes into vessel 1.1 mm. Smallest cell size 0.125 mm. Good initialization compared to measurements on the injector centerline. Injector Injector starts here Slide 36 T difference in the core region can be as high as 100 K, or even more! T profiles At 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 reaction Slide 37 Movie Uniform T vs. Actual T % 900 K Liquid length17.23 Ignition delay16.0 Lift-off length5.3 1100 K 27.5 6.0 8.1 Actual T delays ignition Asymmetric 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!! Slide 38 Random variation in T on top of the mean No T variation T variation +/- 10 K Random variation in temperature on top of the mean (+/- 10 K for 900 K case) Pickett et al. SAE 2010-01-2106 Three random cases tested: % 900 K Liquid length 0.8% Ignition delay2.3 Lift-off length3.9 Slide 39 Actual temperature distribution in the combustion vessel is very important. Asymmetric flame Significantly affect spray and combustion Suggestions: Experiments: temperature distribution in the < 2 mm region should be measured with capable instruments Simulations: use this actual temperature distribution. Better chemical mechanism for n-dodecane!! Conclusion and Suggestions: Slide 40 Thanks Michal Davis for providing the code of global sensitivity analysis. Thanks Lyle Pickett, Maarten Meijer and Julien Manin for the useful discussions. Acknowledgement