The interaction of a vortex pair with a premixed flame serves as an important prototype for premixed turbulent combustion. In this study, we investigate the interaction of a counter-rotating vortex pair with an initially flat premixed methane flame. We compare computational solutions obtained using a time-dependent, two-dimensional adaptive low Mach number combustion algorithm that incorporates GRI-Mech 1.2 for the chemistry, thermodynamics, and transport of the chemical species. We discuss the mechanical nature of the flame-vortex interaction and the features of the interaction that are strongly affected by fuel equivalence ratio, . We find that the circulation around the vortex scours gas from the preheat zone in front of the flame, making the interaction sensitive to equivalence ratio. For cases with 1, the peak mole fraction of CH across the flame is relatively insensitive to the vortex, whereas for richer flames we observe a substantial and rapid decline in the peak CH mole fraction, commencing early in the flame-vortex interaction. The peak concentration of HCO is found to correlate, in both space and time, with the peak heat release across a broad range of equivalence ratios. The model also predicts a measurable increase in C2H2 as a result of interaction with the vortex and a marked increase in the low-temperature chemistry activity.

The interaction of a vortex pair with a premixed flame serves as an important prototype for premixed turbulent combustion. In this study, the authors investigate the interaction of a counter-rotating vortex pair with an initially flat premixed methane flame. The authors focus on characterizing the mechanical nature of the flame-vortex interaction and on the features of the interaction strongly affected by fuel equivalence ratio. The authors compare computational solutions obtained using a time-dependent, two-dimensional adaptive low Mach number combustion algorithm that incorporates GRI-Mech 1.2 for the chemistry, thermodynamics and transport of the chemical species. The authors find that the circulation around the vortex scours gas from the preheat zone in front of the flame, making the interaction extremely sensitive to equivalence ratio. For nearly stoichiometric cases, the peak mole fraction of CH across the flame is relatively insensitive to the vortex whereas for richer flames they observe a substantial and rapid decline in the peak CH mole fraction, commencing early in the flame-vortex interaction. The peak concentration of HCO is found to correlate, in both space and time, with the peak heat release across a broad range of equivalence ratios. The model also predicts a measurable increase in C2H2 as a result of interaction with the vortex, and a marked increase in the low temperature chemistry activity.

The detailed dynamical response of flames in turbulent reacting flow involves a complex interaction between unsteady flow structures and flame chemistry. Two essential features of this interaction are the unsteady strain-rate and curvature disturbances to the reaction zone. In this work, the authors focus on a single flow length/time scale feature in two dimensions (2D), and its effect on a premixed flame for a range of mixture conditions. In particular, they study the interaction of a premixed freely propagating methane-air flame with a 2D counter-rotating vortex pair in an unbounded domain. In earlier work, they studied this flow using C[sub 1] kinetics, at stoichiometric conditions. Notable observations include the shift of the reaction zone into the products on the vortex-pair centerline, leading to depletion of H, O and OH, and the consequent general drop in reaction rates on the centerline flame segment. Curvature-induced focusing/defocusing effects were observed at the positively curved flame cusp, leading to modifications in internal transport fluxes of various species and radicals in the flame, and associated effects on H production and fuel consumption rates. These results were extended to more detailed kinetics, using other C[sub 1] and C[sub 2] mechanisms, which demonstrated the effect of choice of chemical mechanism on the observed transient flame response. The present study focuses on the dependence of the transient flame response on reactants mixture equivalence ratio. Two reactants mixture conditions are studied: case 1 is a stoichiometric conditions - equivalence ratio[Phi]= 1.0, and case 2 is rich at[Phi]= 1.2. In both cases, the reactants are 20% N[sub 2]-diluted.

The understanding of complex premixed combustion reactions is paramount to the development of new concepts and devices used to increase the overall usefulness and capabilities of current technology. The evolution from laminar spherically propagating flames to turbulent chemistry is a logical and necessary process to study the complex interactions which occur within any modern practical combustion device. Methane-air flames were chosen to observe the mild affects of thermo-diffusive stability. Five primary propane equivalence ratios were utilized for investigation: 0.69, 0.87, 1.08, 1.32, and 1.49. The choice of equivalence ratio was strategically made so that the 0.69/1.49 and 0.87/1.32 mixtures have the same undiluted flame propagation rate, dr/dt. Therefore, in the undiluted case, there are two flame speeds represented by these mixtures. Three vortices were selected to be used in this investigation. The vortex rotational velocities were measured to be 77 cm/s, 266 cm/s and 398 cm/s for the “weakâ€, “medium†and “strong†vortices, respectively. Ignition of the flame occurred in two ways: (1) spark-ignition or (2) laser ignition using an Nd:YAG laser at its second harmonic in order to quantify the effect of electrode interference. Accompanying high-speed chemiluminescence imaging measurements, instantaneous pressure measurements were obtained to give a more detailed understanding of the effect of vortex strength on reactant consumption rate over an extended time scale and to explore the use of a simple measurement to describe turbulent mixing. Further local flame-vortex interface analysis was conducted using non-invasive laser diagnostics, such as particle image velocimetry and planer laser induced fluorescence of the OH radical. The dependence of heat release rate on temperature provides an estimation of the strain rate dependence of the reaction rate.

This book aims to be the reference book in the area of oxyfuel combustion, covering the fundamentals, design considerations and current challenges in the field. Its first part provides an overview of the greenhouse gas emission problem and the current carbon capture and sequestration technologies. The second part introduces oxy-fuel combustion technologies with emphasis on system efficiency, combustion and emission characteristics, applications and related challenges. The third part focuses on the recent developments in ion transport membranes and their performance in both oxygen separation units and oxygen transport reactors (OTRs). The fourth part presents novel approaches for clean combustion in gas turbines and boilers. Computational modelling and optimization of combustion in gas turbine combustors and boiler furnaces are presented in the fifth part with some numerical results and detailed analyses.

A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.