University of Wisconsin -- Engine Research Center slide 1 Counter-flow diffusion flame ME Project Chi-wei Tsang Longxiang Liu Krishna P

University of Wisconsin -- Engine Research Center slide 2Content Introduction Case Setup  General description  Model description Reaction mechanism Combustion Model PaSR(Partial Stirred Reactor) CTC(Characteristic Time Scale Model) Result & Comparison General Overview Combustion Model Reaction Mechanism Turbulence Model Conclusion

University of Wisconsin -- Engine Research Center slide 3 Introduction Counter flow gas burner used in both residential and commercial heating and power generation. Goal of the study is to understand the effects of  Combustion model  Chemical mechanism  Turbulence model We compare temperature, species mass fractions, equivalence ratio, and velocity profiles for each case

University of Wisconsin -- Engine Research Center slide 4 Reaction Mechanism & Chemistry Solver GRI 3.0 Mechanism -325 reaction 53 species Lindstedt and Jones - 4 reaction 7 species Global reaction - 1 reaction 5 species Chemistry Solver Used ode solver Rosenbrock43 (built-in); For global reaction and Jones mechanism Speedchem* For GRI mechanism 7 times faster than default ode solver in OpenFoam *Perini, F., Galligani, E., & Reitz, R. D. (2012). An analytical Jacobian approach to sparse reaction kinetics for computationally efficient combustion modeling with large reaction mechanisms. Energy & Fuels, 26(8),

University of Wisconsin -- Engine Research Center slide 5 Combustion Model PaSR Partially stirred reactor model  Computational cell splits into two different zone (reacting and non-reacting)  Model formulation Turbulent mixing time scale: Mixing ratio: C mix = 0.5 for our case

University of Wisconsin -- Engine Research Center slide 6 Combustion Model-Characteristic Timescale (CTC) Model is based on time scales  Rate given by  Characteristic time t l = laminar time scale, time to attain equilibrium t t = turbulent time scale t t = C 2 k/epislon C 2 depends on turbulence model f = delay coefficient = (1 – exp –r )/(0.632) Determines the controlling effects of turbulence r = (amount of product)/(total reactive species)

University of Wisconsin -- Engine Research Center slide 7 Case Setup

University of Wisconsin -- Engine Research Center slide 8 Fuel – Methane Thermal Properties – Janaf Tables Transport Property – Sutherland Transport Equation Schmidt and Lewis numbers are assumed to be unity Turbulence Properties – Turbulent Kinetic energy (k) – 3.75e-5 m 2 /s 2 Turbulent Dissipation ( ε ) – 50 m 2 /s 3

University of Wisconsin -- Engine Research Center slide 9 Test Cases MechanismTurbulenceCombustion BaselineGRIPaSR Case 1GRILaminarNone Case 2GRINone Case 3Single-stepPaSR Case 4Four-stepPaSR Case 5GRICTC

University of Wisconsin -- Engine Research Center slide 10 Results & Comparison

University of Wisconsin -- Engine Research Center slide 11 Qualitative Analysis of the Baseline Case

University of Wisconsin -- Engine Research Center slide 12 Velocity and temperature

University of Wisconsin -- Engine Research Center slide 13 Fuel (CH 4 ) and Oxygen

University of Wisconsin -- Engine Research Center slide 14 C 2 H 2 and NO

University of Wisconsin -- Engine Research Center slide 15 OH and H 2 O 2

University of Wisconsin -- Engine Research Center slide 16 Comparison of Combustion Model

University of Wisconsin -- Engine Research Center slide 17 Combustion Model Comparison

University of Wisconsin -- Engine Research Center slide 18 Combustion Model Comparison

University of Wisconsin -- Engine Research Center slide 19 Short Summary Combustion model seems to have a significant effect on the flame structure Laminar case has the highest temperature CTC seems to follow similar trend as laminar PaSR has the lowest temperature resulting in lower conc. of NO x It seems for laminar and CTC model the flame thickness is smaller hence might require greater resolution to resolve it

University of Wisconsin -- Engine Research Center slide 20 Comparison of Reaction Mechanism

University of Wisconsin -- Engine Research Center slide 21 Comparison of Reaction Mechanism

University of Wisconsin -- Engine Research Center slide 22 Comparison of Reaction Mechanism

University of Wisconsin -- Engine Research Center slide 23 Short Summary All three mechanisms predict the steady state flame location and temperature similarly. Single step has longer ignition delay while the 4-step mechanism has shorter ignition delay compared to GRI mechanism. It does not seem reasonable to predict species concentration using 4-step mechanism.

University of Wisconsin -- Engine Research Center slide 24 Comparison of turbulence model

University of Wisconsin -- Engine Research Center slide 25 Comparison of turbulence model Comparison of turbulence model

University of Wisconsin -- Engine Research Center slide 26 Comparison of turbulence model Comparison of turbulence model

University of Wisconsin -- Engine Research Center slide 27 Short Summary Turbulence results in the delay of combustion It expands the combustion region It has greater impact on the flame development than on steady state

University of Wisconsin -- Engine Research Center slide 28 Conclusion Combustion model impact ignition timing, flame structure and emission Single step mechanism is sufficient to predict the steady state flame location and temperature, but to get better transient analysis and emission prediction we require detailed mechanism. Turbulence makes the flame region larger

University of Wisconsin -- Engine Research Center slide 29Bibliography [1] [2] Jones, W. P., & Lindstedt, R. P. (1988). Global reaction schemes for hydrocarbon combustion. Combustion and Flame, 73(3), [3] Golovitchev, V. I., Nordin, N., Jarnicki, R., & Chomiak, J. (2000). 3-D diesel spray simulations using a new detailed chemistry turbulent combustion model(No ). SAE Technical Paper. [4] Perini, F., Galligani, E., & Reitz, R. D. (2012). An analytical Jacobian approach to sparse reaction kinetics for computationally efficient combustion modeling with large reaction mechanisms. Energy & Fuels, 26(8),

University of Wisconsin -- Engine Research Center slide 30

University of Wisconsin -- Engine Research Center slide 31