Inhibition of plasma-assisted ignition in hydrogen-oxygen mixtures by hydrocarbons

The effect of C2H4 and C2H6 addition on the ignition of a stoichiometric hydrogen:oxygen mixture was experimentally analyzed using a shock tube with a discharge cell. Ignition delay time was measured behind a reflected shock wave after a high-voltage nanosecond discharge and in its absence using mixtures with small percentages of hydrocarbons. The obtained results were compared with ignition delay times in a mixture without hydrocarbon addition. It was shown that C2H4 and C2H6 inhibit the hydrogen-oxygen reaction and that the inhibition effect is much more profound when the mixtures are ignited after a high-voltage nanosecond discharge. A numerical simulation of the discharge and ignition phases was used to show the main mechanisms that control the inhibition of hydrogen:oxygen ignition by hydrocarbons. The densities of atoms, radicals, excited particles and charged particles produced in the discharge plasma were calculated and used as input parameters for ignition modeling. Reasonable agreement was obtained between the calculated and measured plasma-assisted ignition delay times in the mixtures under consideration. The analysis of primary reaction pathways for hydrocarbon species was used to demonstrate the inhibition mechanisms of ignition in hydrogen:oxygen mixtures excited by non-equilibrium discharge plasma.