Development of a Chemistry Dynamic Load Balancing Solver with Sparse Analytical Jacobian Approach for Rapid and Accurate Reactive Flow Simulations

In addressing the demands of industrial high-fidelity computation, the present study introduces a rapid and accurate customized solver developed on the OpenFOAM platform. To enhance computational efficiency, a novel integrated acceleration strategy is introduced. Initially, a sparse analytical Jacobian approach utilizing the SpeedCHEM chemistry library was implemented to increase the efficiency of the ODE solver. Subsequently, the Dynamic Load Balancing (DLB) code was employed to uniformly distribute the computational workload for chemistry among multiple processes. Further optimization was achieved through the introduction of the Open Multi-Processing (OpenMP) method to enhance parallel computing efficiency. Lastly, the Local Time Stepping (LTS) scheme was integrated to maximize the individual time step for each computational cell, resulting in a noteworthy minimum speed-up of over 31 times. The effectiveness and robustness of this customized solver were systematically validated against three distinct partially turbulent premixed flames, Sandia Flames D, E, and F. Additionally, a comparative analysis was conducted, encompassing different turbulence models, turbulent Prandtl numbers, and model constants, resulting in the recommendation of optimal numerical parameters for various conditions. The present study offers one viable solution for rapid and accurate calculations in the OpenFOAM platform, while also providing insights into the selection of turbulence models and parameters for industrial numerical simulation.Comment: 41 pages, 13 figure

Fundamental Study on Hydrogen Low-NOx Combustion Using Exhaust Gas Self-Recirculation

Hydrogen is expected to be a next-generation energy source that does not emit carbon dioxide, but when used as a fuel, the issue is the increase in the amount of NOx that is caused by the increase in flame temperature. In this study, we experimentally investigated NOx emissions rate when hydrogen was burned in a hydrocarbon gas burner, which is used in a wide temperature range. As a result of the experiments, the amount of NOx when burning hydrogen in a nozzle mixed burner was twice as high as when burning city gas. However, by increasing the flow velocity of the combustion air, the amount of NOx could be reduced. In addition, by reducing the number of combustion air nozzles rather than decreasing the diameter of the air nozzles, a larger recirculation flow could be formed into the furnace, and the amount of NOx could be reduced by up to 51%. Furthermore, the amount of exhaust gas recirculation was estimated from the reduction rate of NOx, and the validity was confirmed by the relationship between adiabatic flame temperature and NOx calculated from the equilibrium calculation by chemical kinetics simulator software

Primary soot particle distributions in a combustion field of 4 kW pulverized coal jet burner measured by time resolved laser induced incandescence (TiRe-LII)

To develop accurate models for the numerical simulation of coal combustion field, detailed experimental data using laser techniques, which can figure out the basic phenomena in a coal flame, are necessary. In particular, soot is one of the important intermediate substances in a coal flame. This paper is the first paper in the world reporting soot particle size distributions in a coal flame. The spatial distribution of the primary soot particle diameter were measured by the combination of the time-resolved laser induced incandescence (TiRe-LII) method and the thermophoretic sampling (TS) method. The primary soot particle diameter distribution was expressed by the log normal function based on the particle diameter measurement using SEM images obtained from the TS samples. The relative function between the signal decay ratio obtained by TiRe-LII and the primary soot particle diameter was defined based on the log normal function. Using the relative function, the spatial distributions of the primary soot particle diameter with the soot volume fraction were obtained. The results show that the small isolated soot regions instantaneously exist in the entire combustion field. This characteristics is different from spray combustion field. From the ensemble-averaged TiRe-LII images, it was found that the soot volume fraction and the primary soot particle diameter increases with increasing the height above the burner in any radial distance. It was also found that the volumetric ratio of small particles decreases with increasing radial distance at the region close to the burner exit. However, the variation of the soot particle diameter distribution along the radial direction becomes small in the downstream region. This tendency is caused by the turbulent mixing effect. It is expected that the accurate soot formation model will be developed in the near future by using the data reported in this paper