Characteristic chemical time scale analysis plays a key role in the understanding of turbulence–chemistry interaction in turbulent combustion research and is also an important basis for the selection or development of combustion models in turbulent combustion modeling. A new method named main direction identification (MDID) was developed based on the modification of the CTS-ID (chemical time scale identification) method to achieve the function of identifying the characteristic time scale. Direction weight factor combined with mole fraction limit were used as a criterion in MDID to determine the characteristic time scale. MDID was applied to study characteristic chemical time scales of a CH4–O2 inverse diffusion flame in hot syngas coflow, which is a model flame developed before to study the combustion process in partial oxidation reformers. Results show that the chemical time scale given by the MDID method is about 10–5 s in the combustion area and 10–2 s in the reforming area. The main reaction pathway w...