Amodel for plasma assisted combustion of ethylene-air mixtures at conditions typical for scramjet combustion chamber is developed combining classical mechanisms of thermal combustion with non-thermal plasma chemistry. Numerical simulations showed that sufficiently strong reduction of ignition induction time at a reasonable energy cost can be realized with help of filamentary discharges. Starting from the discharge region, the gas mixture is heated due to exothermic reactions involving atomic oxygen and secondary chemical radicals. Temperature increment to the end of this stage for ethylene-air mixture is relatively small. An important effect of this stage is not heating but production of transient species. Then, a period with slow growth of temperature follows, which terminates by fast combustion. Processes causing the first fast growth of gas temperature are analyzed, and intermediate species controlling acceleration of ignition are determined numerically for plasma assisted combustion of stoichiometric mixture of ethylene with air. The value of the calculated induction time defined as a moment of the fast combustion is rather sensitive to the particular combustion mechanism adopted. This manifests a necessity to refine combustion mechanisms for conditions typical for scramjet combustion chamber with plasma initiation - one atmosphere pressure, static gas temperature around 700 K and appearance of atomic oxygen&dR.