With increased interest in reducing emissions, the axial (sequential) stage combustion concept for gas turbine combustors and high exhaust gas recirculation rates for internal combustion engines are gaining in popularity. Despite the air-quality benefits of these technologies, introduction of inert combustion residuals into a combustion media affects the flame reactivity and stability. This dissertation examines the dilution effect on laminar flame characteristics of iso-octane/air, high/low research octane number gasoline/air, and methane/air mixtures through both experiments and numerical simulations.Spherically expanding flames under constant pressure are employed in an optically accessible constant volume combustion chamber to measure fundamental characteristics of premixed flames. Spherically expanding flames are severely affected by flame stretch in the early stage of combustion and therefore stretch models are of great importance in determining the uncertainty of experimental laminar flame speeds and burned gas Markstein lengths. In order to prevent the existing large scatter in experimental data of these two fundamental flame parameters, the effect of the lower radius limit for the flame speed calculation on extrapolation results of the stretch models is investigated in Chapter 3. Results show that there is a critical lower radius limit, where all laminar flame speed and burned gas Markstein length values obtained by the extrapolation of the stretch models converge to the same laminar flame speed and burned gas Markstein length.Chapter 4 presents the exhaust gas recirculation effect on CO2-diluted iso-octane/air and high/low research octane number gasoline/air mixtures at 1 bar and 373-473 K. The results of the measurements reveal that flame speeds of commercial gasolines do not vary significantly with the research octane number whereas the iso-octane flame speeds are consistently slower than those of gasoline. Numerical analyses are used to determine the dilution, thermal-diffusion, and chemical effects of the CO2 dilution on the flame speed, stretch, and stability.Over the years, many studies have investigated diluted methane flame characteristics with one of the main exhaust gases or a mixture of two. Chapter 5 experimentally and computationally shows that real combustion residuals cannot be accurately represented with only one or two of the main exhaust gases, as the thermodynamic properties and chemical reactivities of the combustion residuals are very distinctive and vary with temperature, pressure, and equivalence and dilution ratios. In Chapter 5, laminar burning velocity and burned gas Markstein length correlations are developed from the methane/air flame measurements at 1-5 bar, 373-473 K, and with 0-15% dilution. The physical and chemical aspects of changes in the laminar burning velocity and flame front stability due to changes in temperature, pressure, and equivalence and dilution ratios are discussed in detail.
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