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This thesis presents pioneering experimental and numerical studies on three aspects of the combustion characteristics of lean premixed syngas/air flames, namely the laminar flame speed, extinction limit and flammability limit. It illustrates a new extinction exponent concept, which enriches the combustion theory.

Above all, the book provides the following: a) a series of carefully measured data and theoretical analyses to reveal the intrinsic mechanisms of the fuel composition effect on the propagation and extinction of lean syngas/air flames; b) a mixing model and correlation to predict the laminar flame speed of multi-component syngas fuels, intended for engineering computations; c) a new “extinction exponent” concept to describe the critical effects of chemical kinetics on the extinction of lean premixed syngas/air flames; and d) the effects and mechanism of the dilution of incombustible components on lean premixed syngas/air flames and the preferential importance among the thermal, chemical and diffusion effects.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
Synthesis gas (syngas) combustion is an attracting topic in both industry and academia. Understanding the combustion properties of syngas is crucial for the efficient, effective and environment-friendly utilization of syngas fuels. This chapter presents an introduction to the propagation and extinction of the lean premixed laminar syngas/air flames. The relevant studies and previous efforts into this topic were systematically reviewed and the key problem and remaining scientific issues were identified. Detailed objectives of this dissertation were proposed and the organization of this dissertation was briefly introduced.
Yang Zhang

Chapter 2. Experimental Approach

Abstract
The experimental approach of this dissertation was introduced and described in detail. The laminar flame speed and extinction limit of the laminar lean premixed syngas/air flames were measured using the counterflow flame method integrated with a particle image velocimetry system. According to the futures of syngas flames, the data processing method was carefully designed and verified. In order to eliminate the disturbance caused by the natural convection, the extinction of weakly-stretched syngas/air flames were carried out under the micro-gravity condition. The uncertainty of the experimental measurements was cautiously estimated to guarantee the accuracy of the experiments, and the uncertainty analysis method was provided in detail.
Yang Zhang

Chapter 3. Numerical Approach

Abstract
This chapter provides an introduction to the numerical approach used in this dissertation. The laminar flame speed and extinction limit were computed using the Chemkin-II based PREMIX and OPPDIF codes, respectively. The controlling equations and its closure, mathematical algorithm and grid partition were described in detail.
Yang Zhang

Chapter 4. Laminar Flame Speed of Lean Premixed H2/CO/Air Flames

Abstract
This chapter provides an in-depth study on the laminar flame speed of lean premixed H2/CO/air flames. The experimentation covered a broad range of the H2/(H2 + CO) volumetric ratio. The performance of chemical kinetic mechanisms was verified using the new data. The flame temperature and the chemical kinetics was studied and a semi-empirical correlation for the prediction of the laminar flame speed of lean H2/CO/air mixtures were developed and validated.
Yang Zhang

Chapter 5. Extinction Limit of Lean Premixed H2/CO/Air Flames

Abstract
This chapter provides a detailed investigation into the extinction limit of lean premixed stretched H2/CO/air flames. Systematic experimentation was conducted detailed the simulation using Chemkin was carried out. Base on the experimental and numerical results, the chemical kinetic characteristics was in particularly studied and an “extinction exponent” was proposed. The molecular transport phenomena in the near-limit weakly stretched H2/CO/air flame was studied under micro-gravity conditions and the effect of the preferential diffusion of H2 was quantitatively assessed.
Yang Zhang

Chapter 6. Lower Flammability Limit of H2/CO Mixtures

Abstract
New experimental investigations into the lean flammability limit of syngas fuels was conducted. The validity of L-C rule was verified using the newly measured experimental data.
Yang Zhang

Chapter 7. Dilution Effect on the Propagation and Extinction of Lean Premixed Syngas/Air Flames

Abstract
The dilution effects of inert components N2 and CO2 on the propagation and extinction of lean premixed H2/CO/air syngas flames were experimentally and numerically investigated. It was found that CO2 dilution had more profound effect on flame propagation and extinction than N2 dilution. The three effects, probably caused by the presence of CO2 and N2 diluents, namely the thermal effect, the diffusivity change effect and the chemical effect, and their preferential importance were numerically assessed. The thermal effect dominated the overall dilution effect in reduction of laminar flame speed and extinction strain rate. The chemical effect caused by CO2 dilution was slightly stronger to the reduction of extinction limit than to that of laminar flame speed. The diffusivity change effect is negligible for both CO2 and N2 diluents. N2 only act as a thermal inert in the propagation and extinction of the H2/CO/air flames.
Yang Zhang

Chapter 8. Conclusion and Recommendation

Abstract
This chapter provides the conclusion of this dissertation and the recommendation to the further work.
Yang Zhang
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