Combustion Modeling

Combustion, which involves the interaction of many processes — including heat and mass transfer, chemical reaction and fluid dynamics — can be modeled with relatively high certainty using computational fluid dynamics (CFD). A properly validated CFD model can predict profiles of velocity, temperature and species concentrations, particle trajectories, pollutant formation, reaction rates and heat fluxes. It can reduce the range of experiments required to understand and optimize an existing process, and can be used as a design tool for next-generation technologies.

Temperature distributions (K) for swirl numbers of (a) 0.9 and (b) 0.06.

A comprehensive CFD model for pulverized coal combustion includes sub-models for turbulence, particle injection, devolatilization, char combustion, radiation, ash fouling and slagging and pollutant formation for nitrogen oxides (NOx), sulfur oxides (SOx) and soot. At LACER and Washington University in St. Louis (WUSTL), we have powerful computational resources to perform high-quality CFD simulations. There are two clusters in LACER dedicated to computational studies. Small-scale simulations are performed with our SPOC LINUX cluster using four parallel INTEL I7-3930K six-core 3.2 GHz processors. For larger-scale simulations, we use our dedicated Chernobyl LINUX cluster, a high-performance cluster with 12 compute nodes and one head node, all running Scientific Linux. The cluster has 240 Intel Xeon E5 compute cores running at 2.5 GHz and 1536 GB ECC DDR3 RAM running at 1866 MHz. WUSTL also provides access to high-performance computing resources.

In LACER, CFD models are built to simulate various combustion processes. We closely compare numerical and experimental results to gain a greater understanding of the underlying physics and chemistry so that we’re able to design and optimize these combustion processes.

The figures above and below are CFD simulations of combustion under extreme conditions. The results show the effects of swirl on flame length and wall heat flux when burning coal in nearly pure oxygen. A longer and thinner flame can be obtained by reducing the swirl number, which subsequently leads to a more uniform and manageable wall heat flux. The CFD results suggest that with proper design the burning of coal in a nearly pure oxygen environment is possible and, that by elongating the combustion zone, the wall heat flux and boiler tube temperature can be maintained at acceptable levels.

Net wall heat flux distribution for the cases shown above.