Zoom meeting link: https://kaust.zoom.us/j/97796826379?jst=2

 

Committee members:

• Ph.D. Advisor: Prof. William L. Roberts
• External Examiner: Prof. Reza Kholghy (Carleton University, Ottawa, Canada)
• Committee Chair: Prof. Yun Hau Ng
• 4th Committee Member: Prof. Bassam Dally

Abstract

Fossil fuels remains essential for the global energy supply, but their combustion produces greenhouse gases. Direct use of carbon-free fuels such as hydrogen (H2) and ammonia (NH3) faces challenges of storage, safety, costs, and altered combustion behavior. Blending these fuels with hydrocarbons provides an intermediate pathway for decarbonization but inevitably leads to soot formation, which influences climate, human health, and combustion performance, including systems used for H2 production. This work investigates the effects of pressure and fuel dilution on soot produced in laminar coflow diffusion flames.

Elastic angular light scattering and extinction were first used on normal diffusion flames (NDF). At atmospheric pressure, H2 substitution enhances soot volume fraction (f_v) and optical parameters (ρ_SA, ω_A), while NH3 substitution suppressed f_v and decreased ρ_SA and ω_A. At elevated pressures, ρ_SA and ω_A exhibit mid-height maximum values, with H2 producing the lowest and NH3 the highest values. Aggregation and restructuring, quantified by radius of gyration (R_gm) and fractal dimension (D_f), indicated a downward shift of the oxidation zone with pressure.

The second part assessed flame stability in inverse diffusion flames (IDF), where data is scarce. Results showed hydrodynamic instabilities dependence on Reynolds numbers and oxygen concentration, which governed toroidal vortex formation. Pressure increased frequency in oscillating buoyancy-driven flames, while jet flow rate dominated frequency in momentum-driven flames. Empirical correlations were established between Strouhal, Froude, and Reynolds numbers.

Next, the effects of fuel dilution with inert and reactive diluents were studied in methane IDFs. Buoyancy enhanced inward radial convection and axial OH expansion. Dilution delayed PAH formation by increasing convection and advection, and displaced soot downstream. CO2 exhibited additional chemical effects, increasing OH concentration which suppressed PAH and soot. 

Finally, soot optical and size parameters were evaluated in methane IDFs at elevated pressures with N2 and CO2 dilution. Pressure promoted soot growth and coalescence of soot particles, while optical parameters correlated negatively with particle number density.

Biography

Raul Serrano-Bayona is a Ph.D. candidate in Mechanical Engineering in the PSE division at KAUST, supervised by Prof. William L. Roberts. He received his Bachelor’s and Master’s degree in Mechanical Engineering from the Universidad Industrial de Santander (Colombia) in 2020. He joined the High-Pressure Combustion research group at the former Clean Combustion Research Center (CCRC) at King Abdullah University of Science and Technology (KAUST) as a Ph.D. Student, in Spring 2021. His research focuses on applying elastic angular light scattering to determine the optical and morphological parameters of soot aggregates in laminar coflow diffusion flames at elevated pressure. His work also includes the use of laser diagnostic techniques for the qualitative measurement of chemical species (OH, NO, PAH), and the analysis of flame instabilities of these flame configuration