DETAILED CHEMISTRY, SOOT, AND RADIATION CALCULATIONS IN TURBULENT REACTING FLOWS
Open Access
- Author:
- Wang, Liangyu
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 17, 2003
- Committee Members:
- Richard C Benson, Committee Member
Robert John Santoro, Committee Member
Andre Louis Boehman, Committee Member
Stephen R Turns, Committee Chair/Co-Chair
Daniel Connell Haworth, Committee Chair/Co-Chair - Keywords:
- oxygen-enriched combustion
thermal radiation
soot modeling
detailed chemistry
turbulent combustion - Abstract:
- The present work aims at a comprehensive approach for the simulation of turbulent reacting flows. In particular, it focuses on the modeling of detailed chemistry, detailed soot formation and oxidation, and the modeling of detailed radiative heat transfer in gas-phase turbulent flames. In addition, the present work centers on numerical investigations of oxygen-enriched turbulent nonpremixed flames. Issues that arise in calculating detailed chemistry, soot formation and oxidation, and thermal radiation in turbulent reacting flows are reviewed and discussed. %The issues regarding detailed chemistry calculations include the difficulties %of using detailed chemistry, the strategies to overcome the difficulties, %the interactions between turbulence and chemistry, and the models for %the interactions. The issues regarding soot calculations include %current understanding of the sooting processes, the models of the %sooting processes, and the application of the models to turbulent flames. %The issues regarding radiation calculations %include the difficulties of the radiation calculations, the solution methods %of radiative transfer equations, the evaluations of radiative properties of %both gas-phase species and soot particles, the interactions between %turbulence and radiation, and the modeling approaches for the interactions. Two detailed models of turbulent combustion are developed using state-of-the-art models of detailed chemistry, soot, and radiation calculations in turbulent flames. One of the models is based on an empirical description of the turbulent flow field and the other is based on CFD modeling of the flow field. The empirical-description-based model is an extension of Two-Stage Lagrangian (TSL) model of turbulent jet flames. This extension includes the incorporation of a detailed soot model and the improvement of the radiation model. The soot model is a detailed one adopted from Appel-Bockhorn-Frenklach's soot model. The dynamics of soot particles are described by the method of moments adapted to the TSL formulation. The original constant-emissivity radiation model is improved by solving the radiative transfer equation on the spatial configuration of the TSL model using the spherical harmonic P1 method and the discrete ordinate S2 method. The gray medium assumption is employed and the Planck-mean absorption coefficient is used to determine the radiative properties of both gas-phase species and soot particles. With the extended TSL model, the characteristics of soot, radiation and NOx emissions in oxygen-enriched flames are studied. The CFD-based model is based on an engineering CFD code (GMTEC) and it solves the compressible flow equations on unstructured meshes. GMTEC is extended by incorporating a detailed chemistry model, a detailed soot model, and a detailed radiation model. The detailed chemistry model is based on the use of the CHEMKIN libraries, and the calculations of chemistry are accelerated by using the ISAT software. The effective use of ISAT for detailed chemistry in nonhomogeneous systems is outlined. The detailed soot model is adopted from Frenklach's detailed soot model with the method of moments. It is coupled to the three-dimensional CFD code through transport equations of soot moments. Two detailed radiation models are implemented, the P1-gray model and the P1-FSK model. Both models employ the spherical harmonic P1 method for the solution of the radiative transfer equation on three-dimensional unstructured meshes. The P1-gray model employs the gray medium assumption and Planck mean absorption coefficient for radiative property evaluations. The P1-FSK model addresses the nongray nature of the radiative heat transfer by using the full-spectrum k-distribution method. The CFD-based comprehensive model is then exercised to simulated an oxygen-enriched flame. The two detailed models developed have proven to be successful in the simulation of oxygen-enriched turbulent flames. The advantage of the TSL model is its computational economy. It is shown to be capable of predicting the general trends of soot, radiation, and NOx emission with oxygen index, fuel type, and initial jet velocity, but it failed to provide quantitative predictions of flame structure due to its simplistic treatment of the hydrodynamics. The advantage of the CFD-based model is its capability of performing detailed, quantitative predictions and of capturing the strong couplings among soot, radiation, flame structure, and NOx emissions in oxygen-enriched flames. It can be used to identify the key sensitivities in soot and NOx formations, to study the effects of nongray gas-phase and soot radiation, and to study the influence of mixing, fuel type, and oxygen index on the soot formation, NOx emission, and thermal radiation characteristics of oxygen-enriched turbulent flames. The deficiencies of the CFD-based model include the simple turbulent combustion model, neglect of turbulent fluctuations in composition and temperature, and the P1 approximation used to solve the RTE. These are the subjects of ongoing research.