Ali, S.M.

Bastiaans, R.J.M.

English

The present study develops a computation strategy for accurately predicting NOx emissions in laminar H2-air flames diluted with N2 using commercially available Ansys-Fluent software. Reactive flow 2D-CFD computations were performed on 2D-axisymmetric opposed-jet counterflow configurations. The hydrogen chemistry was solved using the latest detailed kinetic model by Konnov (2019). The two approaches adopted for NOx prediction are- (1) the use of fluent inbuilt NOx model and (2) the use of detailed kinetic steps for NOx containing N species from Gri-Mech 3.0 mechanism. The fluent post-processing NO model is coupled with the solved H and OH radical concentrations field from Konnov (2019) mechanism for NO production. Comparison of NO profiles results from details kinetics with fluent inbuilt NOx models was performed for both H2-air premixed and non-premixed flames. For non-premixed flames, hydrogen mole fraction in the fuel was varied from 100 % to 77.5 % to cover the effect of peak flame temperature on NO production. For premixed flames, the equivalence ratio was varied from 0.17 to 2.0 to quantify the effect of NO production from rich to lean regime. Comparing these NO profiles generated from the fluent NOx model with the detailed chemistry (Gri-Mech 3.0) highlights the inconsistency of this inbuilt fluent NOx model. Hence, it is concluded that detailed kinetic models containing N species should be preferred over the inbuilt fluent NOx model for accurate NO predictions

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 Comparison of NOx Predictions in Premixed & Non-premixedLaminar H2-air Flames- Detailed kinetics vs Inbuilt Fluent NOxModelsCitation for published version (APA):Ali, S. M., & Bastiaans, R. J. M. (2022). Comparison of NOx Predictions in Premixed & Non-premixed LaminarH2-air Flames- Detailed kinetics vs Inbuilt Fluent NOx Models. Poster session presented at Physics@Veldhoven2022, Veldhoven, Netherlands.Document license:UnspecifiedDocument status and date:Published: 25/01/2022Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 04. Oct. 2023ABSTRACTThe present study develops a computation strategy for accurately predicting NOx emissions in laminar H2-air flames diluted with N2 using commercially available Ansys-Fluent software. Reactive flow2D-CFD computations were performed on 2D-axisymmetric opposed-jet counterflow configurations. Comparing these NO profiles generated from the fluent NOx model with the detailed chemistry(Gri-Mech 3.0) highlights the inconsistency of this inbuilt fluent NOx model. Hence, it is concluded that detailed kinetic models containing N species should be preferred over the inbuilt fluent NOxmodel for accurate NO predictions.Keywords:- NOx predictions; opposed jet counterflow configuration, H2-air premixed & non-premixed flames; Reactive flow 2D-CFD computations; NOx chemistryINTRODUCTIONPower & Flow Group, Department of Mechanical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612 AZ, Eindhoven, Netherlands*a.syed.mughees@tue.nlS.M. Ali*, R.J.M Bastiaans Comparison of NOx Predictions in Premixed & Non-premixed Laminar H2-air Flames-Detailed kinetics vs Inbuilt Fluent NOx ModelsFigure 1 shows one such gas-turbinecombustor design by Thomassen Energyworking on pure hydrogen as a fuel.Besides CO2, NOx emission prediction andits reduction is the other focus forcombustion researchers.GOALDevelopment of fast computationalmethodology for NOx prediction inHydrogen GT Combustion.Fig. 1: Design of FlameSheetTM combustion system byThomassen Energy retrofitted for High Hydrogen GasTurbine Retrofit Project [1,2]Natural gas               HydrogenCOMPUTATIONAL METHODOLOGYISSUEGas turbine working on natural gas leads to CO2 emissions leading to climate change.SOLUTIONUse of Hydrogen as fuel instead natural gas eliminate CO2 emissions completely.COMPUTATIONAL DOMAIN AND BOUNDARY CONDITIONSSOLVER DETAILS FOR SIMULATION• 2D axisymmetric domain constructed for opposed jet counterflow configuration.• Konnov (2019) kinetic mechanism used.• A fixed value of 100 s-1 of global strain rate (𝒂𝒈) was used.• Non-premixed combination of H2/N2 and air.• Premixed mixture of H2/Air at equivalence ratio of 0.25.Fig. 2: Schematic of the computational domain with imposed boundary conditions (a) Non-premixed flame, (b) Premixed flameRESULT AND DISCUSSION𝑿𝟐𝟎𝟎𝝁𝒎𝑿𝟏𝟎𝟎𝝁𝒎𝑿𝟓𝟎𝝁𝒎𝑿𝟐𝟓𝝁𝒎𝑿𝟏𝟎𝟎𝝁𝒎𝑿𝟓𝟎𝝁𝒎𝑿𝟐𝟓𝝁𝒎CONCLUSION• Inconsistency in the Fluent NO models with detailed kinetics is confirmed.• This inconsistency is much larger for Non-premixed flames in comparison to premixedflames.• The accuracy of the detailed kinetic model should also be established by comparing theresults with experimental data.REFERENCESACKNOWLEDGEMENTSRijksdienst voor Ondernemend Nederland for financial support for this study (RVO-HighHydrogen Gas Turbine Combustor High Pressure Test DEI120081).1. High Hydrogen Gas Turbine Retrofit Project Update - Thomassen Energy BV2. Stuttaford, P., Jorgensen, S., Hui, T., Chen, Y., Rizkalla, H., and Oumejjoud, K., 2017. US Patent 9,752,781 B2.3. Fluent, A. N. S. Y. S. (2017). 18.0 ANSYS Fluent theory guide 18.0. Ansys Inc.4. Smith, G. P. (1999). GRI-Mech 3.0. http://www. me. berkley. edu/gri_mech/.5. S.M. Ali; R.J.M Bastiaans., 8th Brazilian Combustion Institute Summer School of Combustion, Soc 2021, Brazil, 18-22 October 2021.6. S.M. Ali; R.J.M. Bastiaans. Efficient Computational Methods for Turbulent Boundary-layer H2-air Flashback Prediction, In ComburaSymposium, Soesterberg, The Netherlands, 10-11 Nov 2021.7. S.M. Ali; R.A.J Julien; Mukundakumar, N; R.J.M Bastiaans. ASPACC 2021- 13th Asia-Pacific Conference on Combustion, ADNEC AbuDhabi- United Arab Emirates, 5–9th December 20218. Konnov, Alexander A. Combustion and Flame 203 (2019): 14-22.(a) (b)RESULT AND DISCUSSIONFUEL INLETOXIDIZER INLETAXIS (axi-sym)OXIDIZER INLETFUEL INLETFig. 3 Contour of temperature profile and H2O net reaction rate for 12.5H2/77.5N2-air diffusion flame at global strain of 100s-1Figure 3 shows temperature profile and H2Onet reaction rate for 12.5H2/77.5N2-airdiffusion flame at global strain of 100s-1A stable flame is obtained which is close tostagnation plane.The contours in Figure 4 shows NO molefraction production in the thermal zone.Fig. 4 Contour of NO mole fraction rate for 12.5H2/77.5N2-air diffusion flame at global strain of 100s-1REACTANT INLETREACTANT INLETAXIS (axi-sym)REACTANT INLETREACTANT INLETFig. 5 Contour of temperature profile and H2O net reaction rate for H2-air premixed flame at global strain of 100s-1 at equivalence ratio of 0.25Figure 5 shows temperature profile and H2Onet reaction rate for H2-air premixed flameat global strain of 100s-1 at equivalence ratioof 0.25.A twin H2-air premixed flame is obtained asexpected.Premixed flames have 2 order of magnitudeless NO production in comparison to non-premixed flames.Fig. 5 Contour of NO mole fraction for H2-air premixed flame at global strain of 100s-1 at equivalence ratio of 0.25Figs. 6(a,b,c,d) Comparison of NO and temperature profiles for Non-premixed and premixed flames- Detailed kinetics vs fluent NO modelFluent NO models areincapable for predicting NOmole fraction for H2-air non-premixed flames (3 order ofmagnitude difference).Identical temperature profileirrespective of NO modelsused.Two order of magnitude lessNOx production by H2-airpremixed flames incomparison to non-premixedflames.

Comparison of NOx Predictions in Premixed &amp; Non-premixed Laminar H2-air Flames- Detailed kinetics vs Inbuilt Fluent NOx Models

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Comparison of NOx Predictions in Premixed & Non-premixed Laminar H2-air Flames- Detailed kinetics vs Inbuilt Fluent NOx Models

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Comparison of NOx Predictions in Premixed &amp; Non-premixed Laminar H2-air Flames- Detailed kinetics vs Inbuilt Fluent NOx Models

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Comparison of NOx Predictions in Premixed & Non-premixed Laminar H2-air Flames- Detailed kinetics vs Inbuilt Fluent NOx Models