What determines a substance’s autoignition point? Why do I find that the auto-ignition temperature of acetic acid is lower than that of propylene?

This post was last edited by 0237967500 on 2010-11-3 at 16:22. The autoignition point refers to the lowest temperature at which a combustible material can ignite spontaneously under specified conditions; this temperature is known as the material’s autoignition point. 　　The main ways in which combustible materials catch fire spontaneously are: (1) heat generation through oxidation ； (2) Dissociation heat ； (3) Polymerization exotherm ； (4) Adsorption exotherm ； (5) Heat release during fermentation ； (6) Reaction of the active substance with water ； (7) Mixing of combustibles with strong oxidizers. 　　 Main factors affecting the autoignition temperature of liquid and gaseous combustibles: Pressure: The higher the pressure, the lower the autoignition temperature ； Oxygen concentration: The higher the oxygen concentration in the mixture, the lower the auto-ignition temperature ； Catalysis: Active catalysts can lower the autoignition point, while inert catalysts can raise it ； Material and inner diameter of the container: Different materials for the container walls have different catalytic effects ； The smaller the container diameter, the higher the auto-ignition temperature. 　　 Main factors affecting the autoignition temperature of solid combustibles: Heating and melting: After melting, it can behave like a liquid or a gas ； Amount of volatiles: The more combustible substances that evaporate, the lower its auto-ignition point ； Particle size of solids: The finer the solid particles, the greater their specific surface area, and the lower their auto-ignition temperature ； Heating time: When combustible solids are exposed to heat for an extended period, their autoignition temperature decreases. The above is the content from Baidu Baike. I also checked that acetic acid is flammable and classified as Category A; the ignition temperature of propylene is 460 degrees, while that of acetic acid is 465 degrees. Therefore, acetic acid has a lower ignition temperature than propylene. The ignition temperature of methane is 540 degrees. In fact, there is no relationship between the ignition temperature of a substance and its vapor pressure. I look forward to answers from those with more knowledge

I checked in the \"Great Dictionary of Chemistry and Chemical Engineering\" and found that the natural boiling point of acetic acid is 426°C; it seems impossible to trust such information from a dictionary:dizzy: