Low temperature oxidation and pyrolysis of n-heptane in nanosecond-pulsed plasma discharges

Initiation of hydrocarbon oxidation and pyrolysis using non-equilibrium plasma discharges has potential applications in combustion and fuel conversion processes opening new fields for cleaner engines or for selective production of chemical products. The parametric effects of oxygen concentration Ar dilution and plasma discharge frequency on pyrolytic and oxidative reaction pathways of n-heptane assisted by non-equilibrium plasma discharge were studied. Low temperature reaction pathways of n-heptane/O₂/Ar mixtures with a nanosecond repetitively pulsed plasma discharge were examined in both in situ time-dependent TDLAS and steady state gas sampling diagnostics. Fuel consumption was more effective in higher Ar than higher oxygen concentrations indicating that higher electron number densities with Ar dilution were more effective than direct electron impact dissociation of oxygen. Steady state sampling results suggested a linear trend of n-heptane dissociation and product species formation with increasing plasma frequency with different major product species for oxidation and pyrolysis. Formation of a major intermediate species formaldehyde was significantly under-predicted while fuel and water production were overpredicted. Path flux analysis suggested that the fuel consumption and water production come from electron collision dissociation of O₂ leading to O and O(¹D) which go on to react with the fuel molecules leading to OH.