Title:
Assessment and Analysis of Turbulent Flame Speed Measurements of Hydrogen-Containing Fuels
Assessment and Analysis of Turbulent Flame Speed Measurements of Hydrogen-Containing Fuels
Author(s)
Johnson, Henderson
Advisor(s)
Lieuwen, Timothy C.
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Abstract
Global efforts to reduce greenhouse gas emissions and achieve a carbon-neutral economy have spurred the exploration of integrating hydrogen into various aspects of the global energy infrastructure. This can involve incorporating hydrogen into existing power generation applications or utilizing fuels with significant hydrogen content, such as syngas. However, the introduction of hydrogen poses significant challenges due to its potential to greatly impact the combustion process, with many aspects of its behavior not yet fully understood under practical gas turbine operating conditions. This thesis aims to investigate the influence of thermodynamic, fluid mechanic, and fuel factors on the turbulent global consumption speed, ST,GC, across different fuel types containing up to 90% hydrogen. This parameter represents the average rate of conversion of reactants to products relative to a specific iso-surface.
The presented database encompasses three distinct fuel types: H2/CO, H2/CO/CH4/N2, and H2/CH4¬, which represent fuels that are either commonly encountered in practical applications or are of interest for future applications. The latter two fuels are new to the overall Georgia Tech database of turbulent flame speed measurements which increase the amount of high pressure data (up to 20 atm), and add data at preheat temperatures up to 500 K. The addition of this data is of great importance as it allows for further exploration of thermodynamic and fuel effects on ST,GC¬.
The analysis of this database reveals several key findings. Firstly, regardless of whether the unstretched laminar flame speed, SL,0, is held constant, higher pressures lead to an increase in ST,GC across all fuel types. The preheat temperature is also shown to increase ST,GC, but when normalized by the laminar flame speed, it demonstrates a decrease. Moreover, the effects of hydrogen addition in H2/CO and H2/CO/CH4/N2 fuel blends are more pronounced compared to those in H2/CH4 fuels. Building upon prior studies that link these observations to mixture stretch sensitivity, the database is analyzed within the framework of a quasi-steady leading points concept model. In this framework, the maximum stretched laminar flame speed, SL,max, serves as the normalizing parameter. This approach proves effective for the H2/CO fuels discussed in this work, as it captures fuel effects at a fixed pressure and preheat temperature. However, a notable limitation arises in its inability to account for systematic differences in pressure and preheat temperature, indicating the need for a second correlating parameter.
To identify this second parameter, a systematic investigation of three additional dimensionless numbers, namely the turbulent Reynolds number, Ret, time scale ratio, and acceleration ratio, is presented. Each of these numbers represents a different physical phenomenon that could potentially account for the observed variation in the data reported. The addition of Ret was considered in prior work; however, we identify that is insufficient as an appropriate scaling number due to its inconsistent correlation with preheat temperature. The acceleration ratio was introduced as a novel means of attempting to capture the ability of a flame to accelerate relative to the flow field. Similar to the Reynolds number, this approach showed limited ability to capture both pressure and preheat temperature effects; nevertheless, it does offer a new way to think about turbulence-flame interactions. Ultimately, the time scale ratio emerges as the optimal second correlating parameter due to its lesser degree of scatter compared to the acceleration ratio. This finding is significant, as it aligns with prior analyses that incorporated the time scale ratio to quantify non-quasi-steady chemistry effects at the leading point and demonstrates its promise as an appropriate scaling approach across a wide variety of conditions.
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Date Issued
2023-08-14
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Resource Type
Text
Resource Subtype
Dissertation