@article{kundu_scroggins_ameen_2020, title={A Novel In Situ Flamelet Tabulation Methodology for the Representative Interactive Flamelet Model}, volume={192}, ISSN={["1563-521X"]}, DOI={10.1080/00102202.2018.1539715}, abstractNote={ABSTRACT A priori flamelet tabulation methods have been used extensively to model premixed and non-premixed combustion in Reynolds-averaged Navier–Stokes (RANS) and large Eddy simulations (LES). Pre-tabulation of flamelet libraries have led to significant cost reduction of Computational Fluid Dynamics (CFD) simulations. However, these tabulation methods rely on certain simplifying assumptions. The dimensionality of the flamelet manifolds and size of flamelet libraries are also constrained due to memory and computational limitations. This limits the applicability and predictive capability of flamelet models. The traditional representative interactive flamelet (RIF) approach with multiple flamelets on the other hand involves online solution of flamelet equations and presumed probability density function (PDF) integration at each computational cell, making it attractive but computationally expensive and not suitable for LES with large cell counts. The current work discusses the development of a novel methodology that combines the advantages of an online flamelet solver along with the computational efficacy of tabulated models. The novel in situ tabulation approach consists of creating a flamelet table at each computational time step using the unsteady flamelet equations. The flamelets are then integrated in real time based on their respective scalar dissipation rate histories. This approach is capable of including history effects and unsteady chemical kinetic effects as it involves the online solution of unsteady flamelets. Implementation and comprehensive validation of the new framework is carried out against gas-jet flames as well as spray flames at high pressures. The approach is first validated for a partially premixed methane gas-jet flame in a RANS framework. The temperature and species mass fractions are compared against experimental results at different locations of a lifted flame. The approach is able to capture the transient flame characteristics. The model is then validated against an n-dodecane spray flame at high pressures in an LES framework with a 103-species n-dodecane chemistry mechanism. The model is able to capture ignition delays and flame liftoff of the n-dodecane spray over varying ambient temperature conditions. Due to the offsetting of presumed PDF integration cost, the proposed framework is shown to be faster than the traditional RIF approach, and the speedup over RIF increases with an increase in the cell count. This framework enables use of the RIF model for large cell count LES simulations.}, number={1}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Kundu, Prithwish and Scroggins, Joseph and Ameen, Muhsin M.}, year={2020}, pages={1–25} }
 @article{banerjee_kundu_gnatenko_zelepouga_wagner_chudnovsky_saveliev_2020, title={NOx Minimization in Staged Combustion Using Rich Premixed Flame in Porous Media}, volume={192}, ISSN={["1563-521X"]}, DOI={10.1080/00102202.2019.1622532}, abstractNote={ABSTRACT Two-stage combustion of methane/air is studied experimentally and numerically with a focus on achieving ultralow NOx emissions. The primary flame is a rich premixed flame in the porous medium. The flame is stabilized in the range of equivalence ratios from 1.1 to 1.7 using upstream heat extraction. The products of the primary flame are rich in the partial oxidation and reforming products such as CO, H2, and CH4. Due to the self-regulated heat losses from the flame the maximum flame temperature of the primary flame remains close to 1700 K. The rich-flame environment and low-flame temperatures limit NOx formation in the primary flame. The NOx emission index of the primary flame shows a maximum at the equivalence ratio of 1.1 and reduces for richer mixtures. The products of the primary flame are burned in the secondary nonpremixed flame. The products could be intercooled to reduce temperature and minimize NOx formation in the secondary nonpremixed flame. The emission index of the secondary flame increases with the equivalence ratio. Variation of combined emission index shows a minimum value at the equivalence ratio of 1.2. The trend remains consistent with the intercooling of the primary flame products.}, number={9}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Banerjee, Abhisek and Kundu, Prithwish and Gnatenko, Vitaliy and Zelepouga, Serguei and Wagner, John and Chudnovsky, Yaroslav and Saveliev, Alexei}, year={2020}, month={Sep}, pages={1633–1649} }
 @article{kundu_echekki_pei_som_2017, title={An equivalent dissipation rate model for capturing history effects in non-premixed flames}, volume={176}, ISSN={["1556-2921"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84995562566&partnerID=MN8TOARS}, DOI={10.1016/j.combustflame.2016.10.001}, abstractNote={The effects of strain rate history on turbulent flames have been studied in the past decades with 1D counter flow diffusion flame (CFDF) configurations subjected to oscillating strain rates. In this work, these unsteady effects are studied for complex hydrocarbon fuel surrogates at engine relevant conditions with unsteady strain rates experienced by flamelets in a typical spray flame. Tabulated combustion models are based on a steady scalar dissipation rate (SDR) assumption and hence cannot capture these unsteady strain effects; even though they can capture the unsteady chemistry. In this work, 1D CFDF with varying strain rates are simulated using two different modeling approaches: steady SDR assumption and unsteady flamelet model. Comparative studies show that the history effects due to unsteady SDR are directly proportional to the temporal gradient of the SDR. A new equivalent SDR model based on the history of a flamelet is proposed. An averaging procedure is constructed such that the most recent histories are given higher weights. This equivalent SDR is then used with the steady SDR assumption in 1D flamelets. Results show a good agreement between tabulated flamelet solution and the unsteady flamelet results. This equivalent SDR concept is further implemented and compared against 3D spray flames (Engine Combustion Network Spray A). Tabulated models based on steady SDR assumption under-predict autoignition and flame lift-off when compared with an unsteady Representative Interactive Flamelet (RIF) model. However, equivalent SDR model coupled with the tabulated model predicted autoignition and flame lift-off very close to those reported by the RIF model. This model is further validated for a range of injection pressures for Spray A flames. The new modeling framework now enables tabulated models with significantly lower computational cost to account for unsteady history effects.}, journal={COMBUSTION AND FLAME}, author={Kundu, Prithwish and Echekki, Tarek and Pei, Yuanjiang and Som, Sibendu}, year={2017}, month={Feb}, pages={202–212} }
 @inproceedings{wang_raju_pomraning_kundu_pei_som_2014, title={Comparison of representative interactive flamelet and detailed chemistry based combustion models for internal combustion engines}, booktitle={Proceedings of the ASME Internal Combustion Engine Division, Fall Technical Conference, 2014, vol 2}, author={Wang, M. and Raju, M. and Pomraning, E. and Kundu, P. and Pei, Y. and Som, S.}, year={2014} }
 @article{kundu_pei_wang_mandhapati_som_2014, title={Evaluation of turbulence-chemistry interaction under diesel engine conditions with multi-flamelet RIF model}, volume={24}, number={9}, journal={Atomization and Sprays}, author={Kundu, P. and Pei, Y. J. and Wang, M. J. and Mandhapati, R. and Som, S.}, year={2014}, pages={779–800} }