As the supply of natural gas has increased in recent years, oxy-combustion using methane in fuel-rich conditions has become prevalent for generating valuable industrial raw materials such as syngas and ethene. At the same time, incomplete combustion products, e.g., polycyclic aromatic hydrocarbons (PAH) and soot, lower the efficiency of chemical production and put the entire environment in danger. Understanding the chemistry can help us improve the efficiency of these processes.<br/>In experiments done by Köhler et al., methane and oxygen (φ=2.5) were flowed into a high-temperature laminar flow reactor at atmospheric pressure, and major species along with intermediates were measured by molecular beam mass spectrometry (MBMS). In addition, concentrations of larger aromatic species like phenylacetylene, indene, and naphthalene are quantified in this work, which helps with validation of PAH formation.<br/>Reaction Mechanism Generator (RMG), which can automatically generate pressure-dependent chemical mechanisms for specified conditions, is used to investigate chemistry of C1 to C12 species in the methane rich combustion process. Pressure-dependent rate coefficients are estimated by RMG which first generates a detailed potential energy surface using the one-dimensional master equation, then applies the modified strong collision method to simplify the full master equation model to a single set of phenomenological rates. Simulating the RMG mechanism using a plug flow reactor model shows great agreement with the experimental results. Major species are predicted within 10%; acetylene, which is over-predicted by existing mechanisms like GRI 3.0 and USC-II, matches closer to the measurement. The prediction of benzene is highly accurate in terms of both magnitude and temperature dependence, and the other aromatics are within the measurement uncertainty. This study done by RMG demonstrates the capability in estimating pressure-dependent kinetics from potential energy surfaces and the applicability in predicting pathways from small molecules to aromatics.

Modeling of aromatics formation in fuel-rich methane oxy-combustion with an automatically generated pressure-dependent mechanism

256th National Meeting (2018)

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