Premixed MILD Combustion of Propane in a Cylindrical Furnace with a Single Jet Burner: Combustion and Emission Characteristics Kin-Pang Cheong a, c, Guochang Wang a, Jianchun Mi a*, Bo Wang a, Rong Zhu b, Wei Ren c a College of Engineering, Peking University, Beijing 100871, China b School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China c Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China * Corresponding author. Email: jmi@pku.edu.cn; Tel: +86-010-62767074 Appendix A. Details of the present CFD simulations Figure A1 Grid for the computational domain. Computational fluid dynamic (CFD) simulations are performed using the commercial software packages ANSYS Fluent 16.0 [1]. The steady state Reynolds Averaged Navier- Stokes (RANS) equations of turbulence, species and energy are solved using the finite S1
volume method and the SIMPLE algorithm. The standard k-ε model with the standard wall function is taken for modeling the turbulent flow and the eddy dissipation concept (EDC) model with a reduced reaction mechanism of propane [2] is utilized to capture the combustion chemistry in the furnace. The present reaction mechanism of propane contains 30 species and 76 reversible elementary reactions and no nitrogen chemistry is included. Discrete ordinates model (DO) with domain-based weighted-sum-of-gray-gases model (WSGGM) are account for the radiation prediction. Regarding the geometric symmetry, the computational cost can be reduced by simulating only a quarter of the furnace. As Fig. A1 shows, the domain is discretized into about 520,000 hexahedral cells with refinement in the region of high gradients and shear layers. Grid independency is well checked by running coarser and finer grids with about 250,000 and 820,000 cells, see Fig. A2. The boundary conditions for the present simulations are velocity inlet, pressure outlet and temperature wall boundary. The temperature of wall boundary is set through the UDF feature of FLUENT to consist with the measured profiles. All discretization of the governing equations are of the second order and the convergence criterions are set as 10-6 for the energy and 10-5 for all other variables. Temperature (K) 1800 1500 1200 900 600 (a) centerline 1800 1600 1400 1200 1800 1600 1400 1200 (b) x = 400mm 1650 1600 1550 250,000 cells 520,000 cells 820,000 cells 1000 300 350 400 450 500 300 1000 0 200 400 600 800 x (mm) 1500 0 10 20 30 0 30 60 90 120 150 R (mm) Figure A2 Grid independency of the present CFD simulations. S2
Appendix B. Comparisons of different chemical mechanisms in predicting the oxidation and NO formation/reduction of C 3 H 8 in a PSR In order to find out the optimized chemical mechanisms for both the oxidation and NO emission of C 3 H 8 /air mixture in a perfectly stirred reactor (PSR), we have testified three oxidation mechanisms with three NOx sub-mechanisms, resulting in four main mechanisms in total. These four mechanisms are, respectively, the USCMech II [3] with NOx submechanism from GRI-Mech 2.11 [4] (USCIIGRI211), the San Diego mechanism with nitrogen chemistry [5] (SanDiego), the Konnov mechanism release 0.6 [6] (Konnov) and the USCMech II with NOx sub-mechanism from Konnov mechanism, as listed in Table B1. Note that the USCMech II is a well-optimized mechanism for the oxidation of hydrocarbons of C 1 - C 4 and the San Diego mechanism is a compact one that includes only the crucial elementary reactions for the oxidation of hydrocarbons. On the other hand, the Konnov mechanism [6] has considered new initiation step for the prompt NO route, i.e., using CH + N 2 NCN + H instead of CH + N 2 HCN + N, and more detailed reaction steps including higher hydrocarbon molecules/radicals in NO formation to better describe the nitrogen chemistry during combustion. Table B1 Summary for the chemical mechanisms of C 3 H 8 oxidation and NOx formation. C 3 H 8 Oxidation + NOx formation Species Reaction steps USCIIGRI211 (USCMech II [3] + GRI2.11 NOx sub-mechanism [4]) 111+17 784+102 SanDiego [5] 50+14 235+52 Konnov [6] 91+38 775+456 USCIIKonnov (USCMech II [3] + Konnov NOx sub-mechanism [6]) 111+38 784+456 S3
0.01 (a) USCIIGRI211 (b) SanDiego 0.001 1E-4 1E-5 0.01 (c) Konnov (d) USCIIKonnov 0.001 1E-4 1E-5 1000 1100 1200 1300 1400 1000 1100 1200 1300 1400 C3H8_EXP C3H8_CAL CO_EXP CO_CAL CO2_EXP CO2_CAL H2O_EXP H2O_CAL CH2O_EXP CH2O_CAL H2_EXP H2_CAL Figure B1 Predicted oxidations of C 3 H 8 in a PSR (τ = 0.12 s, 1 atm, C 3 H 8 = 2930 ppm, = 1.25) by different mechanisms comparing to the experimental results by Dagaut et al. [7]: (a) USCIIGRI211, (b) SanDiego, (c) Konnov and (d) USCIIKonnov. Figure B1 present the predictions of the oxidation of C 3 H 8 in a PSR under different temperatures by the four mechanisms, together with the experimental results from Dagaut et al. [7]. It is seen that the USCMech II provides better predictions for the oxidation of C 3 H 8 and the NOx sub-mechanism does not affect the result (Figs. B1(a) and B1(d)). Meanwhile, the predictions of NO reduction and HCN formation by Konnov mechanism agrees better with the measurements, as shown in Fig. B2. The predictions of NO and HCN by the USCIIKonnov is very similar with the Konnov mechanism, indicating that the NOx submechanism from Konnov [6] is more suitable than those from GRI-Mech 2.11 and the San Diego mechanism for predicting the NO formation during the combustion of propane. Hence, the combination of the USCMech II and the Konnov mechanism, i.e., the USCIIKonnov mechanism, is chosen to investigate the stability and NO emission characteristics of the premixed MILD combustion of propane in a PSR. S4
(a) = 1.0 0.0010 (a1) USCIIGRI211 0.0008 0.0006 0.0004 0.0002 (a2) SanDiego (a3) Konnov (a4) USCIIKonnov NO-EXP NO-CAL HCN-EXP HCN-CAL 0.0000 1150 1200 1250 1300 1350 1400 1150 1200 1250 1300 1350 1400 1150 1200 1250 1300 1350 1400 1150 1200 1250 1300 1350 1400 0.0010 0.0008 0.0006 0.0004 0.0002 (b) T = 1250 K (b1) USCIIGRI211 (b2) SanDiego (b3) Konnov (b4) USCIIKonnov NO-EXP NO-CAL HCN-EXP HCN-CAL 0.0000 0.8 1.0 1.2 1.4 1.6 1.8 0.0010 0.0008 0.0006 0.0004 0.0002 (c) T = 1400 K (c1) USCIIGRI211 0.0000 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0.8 1.0 1.2 1.4 1.6 1.8 0.8 1.0 1.2 1.4 1.6 1.8 0.8 1.0 1.2 1.4 1.6 1.8 (c2) SanDiego 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0.6 0.8 1.0 1.2 1.4 1.6 1.8 (c3) Konnov (c4) USCIIKonnov NO-EXP NO-CAL HCN-EXP HCN-CAL Figure B2 NO reduction of C 3 H 8 in a PSR (τ = 0.12 s, 1 atm, NO = 1000 ppm) predicted by different mechanisms comparing to the experimental results [7] under : (a) varying temperature with = 1.0 (C 3 H 8 = 2930 ppm), (b) varying with T = 1250 K (C 3 H 8 = 2930 ppm) and (c) varying with T = 1400 K (C 3 H 8 = 2490 ppm). References [1] ANSYS Fluent, Release 16.0. [2] C. Jiménez, B. Cuenot, T. Poinsot, D. Haworth, Numerical simulation and modeling for lean stratified propane-air flames, Combust. Flame. 2002, 128, 1 21. [3] H. Wang, X. You, A. V Joshi, S.G. Davis, A. Laskin, F. Egolfopoulos, C.K. Law, USC mech version II. High-temperature combustion reaction model of H 2 /CO/C 1 -C 4 Compounds. [accessed on 2018 Jan 18]. Available from http://ignis.usc.edu/usc_mech_ii.htm. [4] C.T. Bowman, R.K. Hanson, D.F. Davidson, W.C. Gardiner Jr, V. Lissianski, G.P. Smith, D.M. Golden, M. Frenklach, M. Goldenberg, GRI-Mech 2.11. [accessed on 2018 Jan 18]. Available from: http://www.me.berkeley.edu/gri-mech. [5] F.A. Williams, Chemical-kinetic mechanisms for combustion applications. Center for Energy Research, UCSD, [accessed on 2018 Jan 20]. Available from: web.eng.ucsd.edu/mae/groups/combustion/mechanism.html. S5
[6] A.A. Konnov, Implementation of the NCN pathway of prompt-no formation in the detailed reaction mechanism, Combust. Flame. 2009, 156, 2093 2105. [7] P. Dagaut, J. Luche, M. Cathonnet, Reduction of NO by propane in a JSR at 1 atm: experimental and kinetic modeling, Fuel. 2001, 80, 979 986. S6