In reality, combustion process involves several reactions
The overall stoichiometric chemical reaction is unlikely to occur in nature. The elementary reactions can be classified as;

• Chain initiating
• Chain branching
• Chain carrying
• Chain terminating

Chain branching

The ratio of number of free radicals in the product to the reactant > 1

Chain carrying

The ratio of number of free radicals in the product to the reactant = 1

Chain terminating

The ratio of number of free radicals in the product to the reactant < 1