Seminars

Abstract: The ignition of methane/air and ethylene/air mixtures by nanosecond pulsed discharges (NSPD) is investigated numerically using a zero-dimensional isochoric adiabatic reactor. A combustion kinetics model is coupled with a non-equilibrium plasma mechanism, which features vibrational and electronic excitation, dissociation, and ionization of neutral particles (O₂ and N₂) via electron impact. Ignition simulations encompassing a wide range of pressures (0.5 - 30 atm) and pulsing conditions for each fuel are executed, and it is found that the time to ignition τ depends primarily on initial pressure and energy deposition rate. In order to quantify the benefit gained from plasma-assisted ignition (PAI), τ is compared with a thermal ignition time, which excludes kinetic enhancements brought by electron impact reactions. It is found that for both fuels, PAI leads to a faster ignition at low pressures, while at higher pressures (p₀  < 5 atm), methane/air ignition becomes inefficient. The drop in performance with pressure for methane/air PAI is explored through a series of reaction pathway analyses.

This work was also focused on developing and applying a novel methodology for the reduction of the large detailed mechanism to a smaller skeletal one. The methodology extends the Directed Relation Graph with Error Propagation (DRGEP) approach in order to consider the energy branching characteristics of plasma discharges during the reduction. To this end, new targets that include energy transfers are defined and incorporated in DRGEP. The performance of the novel framework, called P-DRGEP, is assessed for the simulation of ethylene/air ignition by nanosecond repetitive pulsed discharges at conditions relevant to supersonic combustion and flame holding in scramjet cavities, and is found to be greatly superior to the traditional reduction approach applied to plasma-assisted ignition.