Doctor of Philosophy (PhD)


Mechanical Engineering

Document Type



Effect of a forced dilution air jet on air-fuel spray mixing and emissions has been investigated. Temperature measurements have been made at a number of forcing frequencies in the range of 100-1100 Hz and blowing ratios between 6-15. Open-loop flame response to forcing has also been acquired by recording pressure and heat release spectra. The results show that the mean temperature field inside the flame can be altered due to jet modulation. Significant effects are observed by forcing at locations close to the dump plane. Enhancements in temperature of the order of 100–200 ˚C, and reduction in pattern factor of the order of 40% were observed. Substantial reductions in nitric oxide emissions can be obtained over a range of flow conditions. More rigorous burning can be obtained due to enhanced fuel air mixing. A multi-resolution technique is utilized to analyze temperature fields to decompose the response of different hierarchical scales to forcing. Forcing is found to have most impact on large-scale structures that are in the order of characteristic jet length scale. Bulk mixing is not the only factor that determines pollutant emissions level. Consequently, there exist select frequencies, which affect both emissions and mixing positively. An artificial intelligence based extremum-seeking algorithm is introduced to optimize the combustor behavior. The second part of this dissertation deals with syngas combustion. Stability of a pre-mixed gas turbine combustor is quite sensitive to fuel composition. Behavior of a premixed confined hydrogen enriched methane flame is studied with regard to thermo-acoustic instability induced flashback, emissions, flammability limits and acoustics over a range of conditions. Hydrogen addition extends the flammability limits and enables lower emissions levels to be achieved. Contrarily, increased RMS pressure fluctuation levels, and higher susceptibility to flashback is observed with increasing hydrogen volume fraction inside the fuel mixture. In addition, a semi-analytical model has been utilized to capture the flame holding and flashback dynamics utilizing G-equation. A limit cycle behavior in the flame front movement is observed due to a non-linearity in the feedback term. Experiments including phase locked radical imaging and PLIF measurements have been performed at varying fuel composition.



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Committee Chair

Sumanta Acharya