CFD Design of Waste Heat Boiler Burner in the Education System of Masters Heat Engineering Specialties

Modern CFD methods for calculating combustion processes make it possible to take into account changes in temperatures, heat loads, rates of coolants, as well as further changes in fuel quality. To develop the skills of CFD design and understanding of combustion processes among future specialists in thermophysical specialties, work was carried out to simulate the burner device of a waste heat boiler. For the study, the design of the gas burner of the waste heat boiler RB-70-4.0-440, which operates as a part of the power unit at the LLC “Rubezhansky Cardboard and Container Plant” in the city of Rubezhnoe, was selected. When constructing a geometric model, the hydraulic resistance to the flow of the supply and distribution manifolds was taken into account. To simplify the calculations, the problem was carried out in a two-dimensional, axisymmetric formulation. Analyzing the computational combustion models, the Non-Premixe Combustion model was chosen, which made it possible to take into account the entry of fuel and oxidizer into the reaction zone by two different flows, as well as turbulent diffusion flame propagation. Six variants of models were investigated: the first three variants with a flame tube with a solid disc with diameters of 32, 48, 56 mm, the next three variants, had a burner with a discontinuous disk 32 mm in diameter at a distance of 6, 16, 32 mm from the flame tube. As a result of the research, the optimal shape of the burner was chosen, which corresponds to model 4, and provides a high-quality combustion process, as evidenced by the high temperature of the torch and the lowest temperature at the disk. The conducted research gives future masters the skills of modeling combustion processes in power equipment.

Computational Fluid Dynamics Study of a Nonpremixed Turbulent Flame Using openfoam: Effect of Chemical Mechanisms and Turbulence Models

This article presents a study of the influence of chemical mechanisms and turbulence models on Reynolds-averaged Navier–Stokes (RANS) simulations of the CH4/H2/N2-air turbulent diffusion flame, i.e., the so-called DLR-A flame. The first part of this study is focused on the assessment of the influence of four chemical models on predicted profiles of the DLR-A flame. The chemical mechanisms considered are as follows: (i) a C2 compact skeletal mechanism, which is derived from the GRI3.0 mechanism using an improved multistage reduction method, (ii) a C1 skeletal mechanism containing 41 elementary reactions amongst 16 species, (iii) the global mechanism by Jones and Lindstedt, (iv) and a global scheme consisting of the overall reactions of methane and dihydrogen. RANS numerical results (e.g., velocities, temperature, species, or the heat production rate profiles) obtained running the reactingFOAM solver with the four chemical mechanisms as well as the standard k − ɛ model, the partially stirred reactor (PaSR) combustion model, and the P − 1 radiation model indicate that the C2 skeletal mechanism yields the best agreement with measurements. In the second part of this study, four turbulence models, namely, the standard k − ɛ model, the renormalization group (RNG) k − ɛ model, realizable k − ɛ model, and the k − ω shear stress transport (SST) model, are considered to evaluate their effects on the DLR-A flame simulation results obtained with the C2 skeletal mechanism. Results reveal that the predictions obtained with the standard k − ɛ and the RNG k − ɛ models are in very good agreement with the experimental data. Hence, for simple jet flame with moderately high Reynolds number such as the DLR-A flame, the standard k-epsilon can model the turbulence with a very good accuracy.

On Predictions of Fuel Effects on Lean Blow Off Limits in a Realistic Gas Turbine Combustor Using Finite Rate Chemistry

The demand for aviation propulsion systems with ever higher power requirements, reliability, and reduced emissions has been steadily increasing. Desirable features for next generation high-efficiency gas turbine engines include improvements in combustion efficiency, fuel economy, and stable operation in the fuel lean limit. Despite recent advances, a significant issue facing gas turbine designers is sustaining flame stability during lean operation, which could otherwise lead to global extinction events, or lean blow out (LBO), resulting in a severe loss of operability, particularly at higher altitudes. Flame stabilization is a complex physical and chemical process which is determined by the competing effects of the rates of chemical reactions and rate of turbulence advection-diffusion of species and energy to and from the flame leading to a local ignition and extinction phenomena. The goal of the present study is to perform a high fidelity numerical investigation of the turbulent diffusion flame in a realistic turbine combustor to evaluate the potential to predict the local lean-blow-off dynamics and to gain more insights of the complex physics. A comparative study on LBO characteristics is performed using Finite Rate Chemistry, Large Eddy Simulation and Adaptive Mesh Refinement, for different fuels using a realistic gas turbine combustor. The fuels investigated include a petroleum based fuel and an alternative fuel candidate. The simulation was broken down in two phases: flame stabilization and a subsequent staged ramp-down of fuel flow rate to initiate LBO. It is shown that the simulations successfully predict LBO occurring at different equivalence ratios for the two fuels. Although, the simulations predict LBO occurring at slightly smaller equivalence (fuel-to-air) ratio than the experimental data, the difference between the equivalence ratios of the two fuels at LBO is very close to the experimental observation.