Over the years methane and natural gas (NG) as a fuel have become an important source of energy in the power generation and transportation sectors, with the latter most prominently adopting propane used in public transportation shuttles. Notable interest in using liquid methane or NG fueled rocket engines has recently gained traction and are currently in development/production at SpaceX (raptor engine, full-flow staged combustion cycle) and Blue Origin (BE-4, staged combustion cycle). Given the variety of applications, sourcing and refinement of methane/NG may be completely different to ensure a certain purity is met, especially in an advanced rocket engine cycle like the raptor engine, that may be highly sensitive to minor fuel variances. The current study seeks to understand the ignition behavior of methane (with and without CO2 dilution) and NG surrogate mixtures, including CH4/C2H6/C3H8 and CH4/C2H6/C3H8/i-C4H10/n-C4H10, using a high-pressure shock tube facility at reflected shock conditions relevant to advanced rocket engines and gas turbine cycles. This included pressures near 16, 100, and 200 bar throughout a temperature range of 1000-1621 K. Ignition delay time data were compared with predictions of a chemical kinetic mechanism, and along with performed sensitivity and pathway analyses, further aided in the understanding of the observed ignition behavior. The combined effects of lower activation energy, increased concentration of OH and CH radicals, and increased heat of combustion all play some role in the observed promotion of ignition. These combined effects are primarily a function of fuel mixture and concentration, and combustion relevant pressure and temperature conditions (reflected shock conditions T5 and P5), which in addition dictate the propensity of preignition and deflagration-to-detonation transition behavior observed in the shock tube.


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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

Mechanical Engineering









Release Date

August 2024

Length of Campus-only Access

3 years

Access Status

Doctoral Dissertation (Campus-only Access)

Restricted to the UCF community until August 2024; it will then be open access.