Gas filtration combustion in porous media differs substantially from the combustion with free flame. A one-dimensional model is proposed, and a perturbation theory is used for the combustion front velocity analysis of the methane-air premixed combustion in an inert packed bed, The temperature distribution is predicted for either fully-developed or transient combustion state, based on direct solution and Green's function method. Finally, computational experiments are given and the results are satisfactory.

The instantaneous response of a laminar diffusion flamelet is investigated numerically. A detailed mechanism GRI-Mech 3.0(53-species and 325-reaction) is empolyed to describe the CH₄ oxidation and NO_x formation. A predication of steady flamelct structures is compared with the experimental data to validate the method. A step variation of strain rate is used to simulate the influence of a instantaneous flow field on the flamelet local structure. The response of flamelet structures(temperature and species concentration) to the strain rate variation is given and analyzed. We focus on the influence of the step size of the strain rate. It is found that the flamelet response to the strain rate variation is not symmetric,and the response time is inverse proportional to the strain rate variation as it is small. In addition, the mean response time of temperature is much longer than the flow time scale of a typical turbulent combustion field, which demonstrates the importance of unsteadiness in the numerical simulation of turbulent combustions.

A lifted turbulent H₂/N₂ jet flame in a hot and vitiated coflow is investigated numerically to explore the issues of autoignition as well as the flame lift-off. The composition probability density function (PDF) method is employed to facilitate the implementation of detailed chemical kinetics. A multiple-time-scale k-ε turbulence model is combined for the calculation of flow and turbulence fields. Detailed chemical reaction mechanisms of hydrogen oxidation are incorporated in the calculation. The predictions are compared with experimental data. The flame lift-off height and auto-ignition process are reproduced accurately by the model.

A piloted CH₄/O₂/N₂ turbulent jet non-premixed flame (Sandia flame D) is numerically investigated.The summary of the adopted models contains a two-scale k-ε turbulence model,the scalar joint probability density function (PDF) transport equation approach,the augmented reduced mechanism (ARM) for methane oxidation (consisting of 16 species and 12 lumped reaction steps),the Euclidean minimum spanning tree (EMST) small scale mixing model etc.The agreements between the numerical results and the experimental data are good,including the scatter plots and conditional PDFs of scalars as well as the scalar averages.The numerical results indicate that the present models are not only able to represent the macro flame structure accurately,but also can successfully predict the complicated local extinction and re-ignition processes in the turbulent combustion.

A consistent hybrid FV/MC algorithm developed on triangular unstructured meshes is implemented to simulate turbulent diffusion flame stabilized on bluff body. Monte Carlo method is used to solve joint fluctuating velocity-frequency-composition PDF equation, while Reynolds averaged mass, momentum and energy equations are solved by finite volume method. The coupling between the two methods reduces the statistical and bias error of stand-alone particle method, so accuracy and efficiency are improved greatly. Laminar flamelet model is incorporated. The simulation results are compared with the experimental data.

The laminar flamelet model in combination with joint probability density function (PDF) transport equation of mixture fraction and turbulence frequency is used to simulate fluctuating behavior of radiative source term in turbulent jet diffusion flames of hydrogen.The frequency distributions of radiative source terms in the combustion zone are calculated. The results show that, for the given ensemble, about 95% samples of radiative source term locate within the region of ±3.0 standard deviation of the mean radiative source term. The profile of frequency distribution indicates having a single peak.

A confined turbulent jet diffusion flame is studied using the probability density function(PDF) approach together with the k-ε two-equation model. The effect of solid wall and pressure gradient on the velocity and scalar is mainly concerned with. Then two confined turbulent combustion fields with different dimensions are simulated, of which the fluid structure, flame structure and flame shape are studied. In the end, the result is analyzed and conclusions are made.