The role of physical and chemical properties of single and multicomponent liquid fuels on spray processes, flame stability, and emissions
Date
2019
Authors
Alsulami, Radi Abdulmonem, author
Windom, Bret, advisor
Marchese, Anthony, committee member
Olsen, Daniel, committee member
Venayagamoorthy, Karan, committee member
Journal Title
Journal ISSN
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Abstract
Ensuring reliable and clean combustion performance of IC engines, such as liquid-fueled gas turbines, is associated to our understanding of the impact of fuel composition and properties, as well as the processes that the liquid fuel experiences, e.g., atomization, vaporization, turbulent mixing, and chemical kinetics, on the combustion efficiency, stability, and emissions. This understanding is a key prerequisite to the development of fuel surrogates and the deployment of alternative jet fuels. Most of the surrogate formulation activities, especially with regard to aviation fuels, have targeted only the gas-phase behavior of the real fuels, often neglecting properties responsible for atomization, vaporization, and fuel/air mixing (i.e., physical properties). In addition, much research has been done to understand the flame stability (e.g., lean blowout limit and flame liftoff height) of gaseous and pre-vaporized fuels. Thus, the optimization of the fuels and the liquid fueled combustion devices, e.g., gas turbines, requires the consideration of the two-phase process and the coupling between the complex physical and chemical processes. This will improve the understanding of the mechanisms that controls flame lean blowout limit and liftoff height of liquid fuels. Therefore, an appropriate surrogates will be formulated and a faster processes to certify the alternative fuels will be achieved. In this work, the flame stability in spray burner, quantified by flame lean blowout liftoff height, for different single, binary, alternative, and conventional fuels were experimentally measured. The flame behavior from the spray burner was compared to the results which was done using gaseous flame platform, e.g., counterflow flame burner, to clearly demonstrate the significant importance of two-phase spray processes (i.e., atomization, vaporization, and turbulent mixing) on flame stability. It was found that the atomization process, which can lead to the variation of the droplet size and distribution, has significant impact on flame stability. This is because any change in the droplet size can enhance/diminish the vaporization and mixing processes, and therefore influence the clean and efficient energy conversion process. In addition, the sensitivity of the fuels properties on flame stability was evaluated to provide an explanation for why certain fuel properties govern flame stability, such as lean blowout and liftoff height. Thus, flame stability mechanisms can be developed. A number of approaches were used in this work to address these issues, such as multiple linear regression analysis, and previously developed correlations. The results indicate the importance of the atomization process (i.e. droplet size) on the vaporization rate and suggest that the liquid fuel fraction entering the flame plays a dominant role in controlling lean blowout limits. Thus, the large droplet and less volatile fuel was the most resistance fuel to flame blowout. The differences in liftoff height was shown to be a result of two-phase flame speed, which accounts for both pre-vaporized fuel reactivity defined by laminar flame speed (SL) and time scales associated with droplet evaporation. The influence of the physical and chemical properties of different jet fuels on spray process and thus on emissions is also investigated. This is done by measuring soot formation using Laser-Induced Incandescence (LII). The trends in spray flame soot formation are compared to the gas-phase Yield Sooting Index (YSI). Results indicate differences in planar soot distributions amongst the fuels and suggest a significant influence of the atomization and the vaporization processes on mixing and the soot formation.
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Subject
energy conversion
jet fuels
spray flame
flame stability
combustion
liquid fuels