Although concerns about carbon dioxide (CO2) emissions and their impact on climate change has led to an increase in renewable energy electricity generation, natural gas power plants remain the dominant source of electricity generation in the United States. Until the capacity of renewable energy sources can meet growing electricity demand, natural gas power generation will likely remain an important source of electricity generation. Supercritical CO2 (sCO2) power generation cycles offer an alternative to traditional gas turbines by reusing and sequestering CO2 from the combustion process to prevent its release into the atmosphere. This study seeks to understand natural gas ignition in highly CO2 diluted mixtures at conditions relevant to sCO2 cycles, as well as rocket engines, using a high-pressure shock tube facility. Experiments were performed using a natural gas mixture (C1-C4 alkanes) with and without CO2 dilution for varying equivalence ratios at pressure up to 213 atm for a temperature range of 1016 K to 1286 K. Experiments were also performed using a second natural gas mixture (C1-C2), as well as using methane for a baseline comparison with similar studies. Ignition delay times were measured using OH radical emission measurements and compared to model predictions. Laser absorption spectroscopy measurements at a wavelength of 3.39 µm were used as a qualitative indicator of methane depletion during ignition. It was found that misinterpretation of OH radical emission measurements for experiments with significant reflected-shock bifurcation suggests better agreement with model predictions than observed using a combination of emission and absorption measurements. A comparison of chemical kinetics models shows inconsistent agreement with methane ignition measurements at 200 bar with CO2 and argon as the primary bath gases. Reaction pathway analysis was conducted to investigate the predicted effects of CO2 on chemical kinetics for these conditions. In addition, model predictions did not capture the effect of CO2 on natural gas ignition at 200 bar for the mixtures and temperature ranges studied. More data is needed to support the refinement of chemical kinetics mechanisms to better model methane and natural gas ignition in CO2 at 200 bar.


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Graduation Date





Vasu Sumathi, Subith


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering




CFE0009004; DP0026337





Release Date

May 2023

Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Open Access)