Computational Study of NO Formation in Hydrogen-Enriched Propane–Air Flames under Different Initial Pressures, Temperatures, and Hydrogen Concentrations

Hydrogen-enriched propane is a potential substitute fuel for various engines, since it burns cleaner than fossil fuels and releases fewer harmful pollutants such as particulate matter, carbon dioxide, and nitrogen oxides (NO_x). Decreases in their levels are essential for reducing the negative impact of greenhouse gas emissions that contribute to climate change. Furthermore, adding hydrogen to hydrocarbon–air mixtures raises the amount of radical species present in the flame front, which in turn increases the reaction rate and laminar burning velocity. In the present study, stoichiometric C₃H₈–H₂–air mixtures with various hydrogen mole fractions (r_H = 0–0.9) under different initial pressures (0.5–2.0 bar) and initial temperatures (300–500 K) were studied to quantitatively examine NO formation in their flames. The NO mass fraction profiles in premixed C₃H₈–H₂–air flames, along with profiles of temperature and important species concentrations, were obtained by kinetic modeling of laminar flame propagation using the GRI 3.0 mechanism. The peak NO mass fractions were examined in correlation with the peak flame temperatures and important radical concentrations, as determined by the partial replacement of propane by hydrogen in the ternary C₃H₈–H₂–air mixtures and by the variable initial pressures and temperatures.