Detailed Chemical Kinetic Modeling of Premixed Laminar Natural Gas Flames Odorized with Methanethiol (CH3SH): Formation and Evolution of Toxic Sulfur Species

Natural gas is routinely odorized with trace sulfur compounds, such as methanethiol (CH3SH), to enable leak detection. Although methane, the primary component of natural gas, is commonly used as the reference fuel in combustion studies, the oxidation behavior of CH3SH in premixed methane flames remains poorly characterized, despite its presence in natural gas, biogas, and refinery streams. This study presents a detailed kinetic mechanism for simulating CH3SH-doped premixed CH4 flames across a broad equivalence ratio range (Φ = 0.7–1.3). Results reveal a strong stoichiometric dependence: lean flames (Φ = 0.7) promote complete oxidation, yielding high concentrations of SO2 and SO3, which pose risks of acid deposition and corrosion. In contrast, rich flames (Φ = 1.3) suppress SOx formation but significantly enhance the production of reduced sulfur species (H2S and CS2) by up to an order of magnitude. Stoichiometric conditions (Φ = 1.0) yield a mixed speciation profile. These findings underscore the critical need for precise equivalence ratio control. We propose staged combustion strategies; employing slightly rich primary zones followed by oxidizing post-treatment as a promising approach for cleaner utilization of odorized natural gas.