Tryethylaluminium (TEA) is known to be hypergolic with oxygen. Hence it is used in semi-cryogenic liquid rocket engines (LRE) along with oxygen as an igniter fuel. The flame produced from such hypergolic combustion can be used as a source of ignition for the fuel-oxygen mixture to produce thrust in the LRE. The present study focusses on the development of a detailed reaction mechanism for ignition and combustion of TEA along with oxygen. Various reactions were identified using quantum mechanics based density functional theory. Optimised molecular structures of the reactants, products and the transition states were identified for the reactions using B3LYP theory with 6-311G ++ (d,p) basis set. The elementary reaction mechanism thus obtained was tested by simulating the ignition and combustion process in a 0-D homogeneous reactor.