Department: Mechanical & Aerospace Engineering
Faculty Advisor(s): Kalyanasundaram Seshadri | Forman A. Williams

Primary Student
Name: Ulrich Niemann
Email: ulnieman@ucsd.edu
Phone: 858-534-6505
Grad Year: 2013

Computational fluid dynamic (CFD) codes require chemical-kinetic mechanisms to simulate combustion processes in practical systems. The principal goal of the present work is to provide experimental data of low molecular weight fuel flames at elevated pressures that can be used to validate these mechanisms. Results of measurements of critical conditions for extinction and of temperature profiles in counterflow diffusion flames are reported. In this configuration a flame is stabilized in the mixing layer that is formed between two counterflowing streams. One stream is made up of fuel mixed with nitrogen and the other stream is air. The fuels tested are hydrogen, methane, ethane and ethylene. An experimental facility was especially constructed for carrying out experiments at pressures up to 20 atm. The range of conditions explored is of interest in practical applications, for instance, gas turbines. This study shows that pressure has a significant effect on the extinction of non-premixed low molecular weight fuel flames. A strong non-monotonicity can be observed, resulting in an increase in flame stability with increasing pressure in the moderate pressure range. After a maximum value is reached the characteristic extinction strain rate decreases with an increase in pressure. This behavior can primarily be explained with competing pressure dependent chain branching and recombination reactions. Even though past theoretical findings already exhibit a good level of understanding of this subject with regards to hydrogen, this is the first experimental evidence that confirms the predicted non-monotonic pressure-dependent extinction behavior of non-premixed hydrogen flames and the first time this investigation has been expanded to hydrocarbon fuels. For the range of pressures investigated here, it has been found that the maximum flame temperature at extinction increases with pressure. In addition, the flame thickness decreases with increasing pressure. The results presented here, will help to improve knowledge of underlying chemical-kinetic and transport parameters at elevated pressures.

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