A numerical study of the auto-ignition temperatures of CH4–Air, C3H8–Air, CH4–C3H8–Air and CH4–CO2–Air mixtures

• A detailed kinetic model is used to predict the auto-ignition temperature of mixtures hydrocarbons.
• The change of components impact on the auto-ignition temperatures is investigated.
• The deviation is about 10% between predicted results and previous study.
• The method can be used to predict auto-ignition temperature of low hydrocarbons.

The auto-ignition temperature (AIT) is an important parameter in the process industries. In order to ensure a safe working environment in process industries, it is important to predict the AIT of combustible gases or vapors. In this study, the AITs of natural gas mixtures (CH4–Air, C3H8–Air, CH4–C3H8–Air and CH4–CO2–Air) are calculated based on a detailed kinetic model. To create a more practical model, different ignition criteria and convective heat transfer coefficients are investigated and compared against one another, resulting in the temperature criterion and a convective heat transfer coefficient of h = 50 W/(m2 K). The results showed that the AITs of CH4–Air and C3H8–Air decrease with an increase of equivalence ratios. While the propane ratio increasing, the AIT of CH4–C3H8–Air decreasing. Reaction path analysis of natural gas mixtures (CH4–C3H8) was also carried out to explain this phenomenon, yielding results showing that C3H8 is the main reaction during the ignition induction period. In addition the AIT of CH4 increases slowly in positive correlation with CO2, which plays a role of an inert gas. Comparing the results with literature work revealed a deviation of about 10%. Thus, it can be reasonably concluded that the AIT of a low hydrocarbons mixtures such as natural gas can be reliably predicted with detailed kinetic model.