Laminar Flamelet Combustion Model Research Articles

LES and Multi-Step Chemical Reaction in Compartment Fires

Numerical studies on two large-scale compartment buoyant fires were performed utilizing a fully coupled Large Eddy Simulation (LES) and strained laminar flamelet combustion model, extended from single-step to multistep chemical reaction. Two Subgrid-Scaled (SGS) turbulent models, Smagorinsky and WALE, were examined for center and corner fires. Compared with the experimental and existing numerical data, the WALE model with a multistep chemical reaction gave the best prediction for the upper hot layer and doorway gas temperatures. Specie concentrations including oxygen, carbon dioxide, and carbon monoxide were also found to compare well against the experimental measurements when the WALE model with a multistep chemical reaction was adopted.

Effects of Hydrogen Addition on the Entropy Generation of Biogas Conventional Combustion

Biogas has a great potential to be applied for heat and power generation throughout the world due to its availability from various resources. However, one of the most important barriers of biogas utilization development is its low calorific value. In order to increase the performance of biogas in industrial application, hydrogen enriched biogas could be substituted. In this paper a set of numerical simulations were conducted to estimate the variation of entropy generation in hydrogen enriched biogas flames due to hydrogen addition to the fuel. Reynolds Averaged Navier Stokes with a second order turbulence closure and laminar flamelet combustion model was applied to compute energy fields and flow in the flame. It was found that hydrogen enrichment resulted in an augmentation in the entropy generation rate of the biogas conventional flame. Such increase could be attributed to the increase in irreversibilities due to biogas flame temperature rise.

Entropy Generation in Turbulent Swirl-Stabilized Flame: Effect of Hydrogen Enrichment

A set of numerical simulations were conducted to estimate the change in entropy generation in swirl stabilized CH4/air flames due to H2 addition to the fuel. A robust finite volume computational model solving the Reynolds Averaged Navier Stokes with a first order turbulence closure and laminar flamelet combustion model was used to compute the flow and energy fields in the flame. Hydrogen enrichment resulted in an increase in the entropy generation rate of the flame. Such increase was attributed to the increase in heat transfer irreversibilities due to flame temperature rise.

Combustion characteristics of H2/N2 and H2/CO syngas nonpremixed flames

Turbulent nonpremixed H2/N2 and H2/CO syngas flames were simulated using 3D large eddy simulations coupled with a laminar flamelet combustion model. Four different syngas fuel mixtures varying from H2-rich to CO-rich including N2 have been modelled. The computations solved the Large Eddy Simulation governing equations on a structured non-uniform Cartesian grid using the finite volume method, where the Smagorinsky eddy viscosity model with the localised dynamic procedure is used to model the sub-grid scale turbulence. Non-premixed combustion has been incorporated using the steady laminar flamelet model. Both instantaneous and time-averaged quantities are analysed and data were also compared to experimental data for one of the four H2-rich flames. Results show significant differences in both unsteady and steady flame temperature and major combustion products depending on the ratio of H2/N2 and H2/CO in syngas fuel mixture.

Turbulence Modeling in a Model Combustor

As a benchmarking of turbulence modeling in diffusion flame combustors, the flow field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was investigated numerically. Solutions obtained from four turbulence models together with a laminar flamelet combustion model and a discrete-ordinates radiation model were compared with a comprehensive database obtained from a series of experimental measurements. It was found that the Reynolds stress model (RSM) illustrates superior performance over three popular two-equation eddy-viscosity models. Although the main flow features were captured by all four turbulence models, only the RSM was able to successfully predict the lengths of both recirculation zones and the turbulence kinetic energy distribution in the combustor chamber. In addition, the RSM provided fairly good predictions for all Reynolds stress components, except for the circumferential normal stress at downstream sections. However, the coupling between the RSM and combustion models needs to be improved to extend its application in practical combustion systems.

Study of premixed turbulent combustion including landau-darrieus instability effects

A new laminar flamelet combustion model has been developed for application to fully premixed turbulent combustion in spark-ignition engines. The new model is applicable to combustion at moderate turbulence intensities typical of conditions in many engines in which laminar flame instability effects can be important. It is formulated in such a way that it reverts to an earlier theoretiecal model by Bray, Moss, and Libby in the case of combustion at high turbulence intensities. At low turbulence intensities, it mimies results of the numerical simulations by Joulin and Cambray. A Markstein number charactereizing the stretch response of a laminar flame appears as a parameter in the model equations. An experiment using laser sheet tomography has been performed that confirms the predicted influence of Markstein number on flame brush structure. Turbulent burning velocities are also predicted using KPP theory. Results are in satisfactory agreement with published data.