| This dissertation presents an experimental study of the application and the underlying physics of transient plasma ignition. Transient plasma generated by nanosecond electrical discharges has demonstrated lean-burn capability and reductions in ignition delay in a variety of engines, resulting in higher combustion efficiencies and lowered emissions compared to conventional spark ignition. The experiments performed demonstrate the effects of transient plasma ignition and attempt to understand the basic physics behind it by examining the production of radicals, conditions for ignition, and combustion characteristics.;Critical to the study of the application of transient plasma is the enabling technology: pulsed power systems. To realize this technology in aircraft and automobile engines, the size, weight, cost, reliability, and electrical energy consumption of the pulsed power systems must be comparable to that of the current spark ignition systems. To that end, a compact, solid state 12 ns pulse generator was developed and successfully implemented in transient plasma ignition experiments.;Transient plasma was applied in both quiescent and flowing fuel-air mixtures in a pulse detonation engine (PDE), an internal combustion engine (ICE), and a constant volume reactor. Reduced ignition delays and lean-burn capability were demonstrated. A 12 ns, 70 mJ pulse was used achieve similar gains as those produced by an 85 ns, 800 mJ pulse, which means that more compact pulse generators may be used for this application. It was demonstrated that water inhibits the performance of TPI, and optical diagnostic techniques were used to determine that this was due to a significant decrease in production of atomic oxygen, which plays an important role in enhancing combustion kinetics.;It was demonstrated that after a transient plasma discharge, ignition kernels are formed at the ends of spatially separated streamer channels, where there is an enhanced reduced electric field (hundreds of Td) and significant energy transferred into electronically excited species. Evidence is presented that transient plasma ignition occurs in two phases; a distinct non-thermal phase of ignition, wherein the efficient production of electronically excited species accelerates reaction rates, and a subsequent thermal phase, driven by exothermic fuel oxidation in reactions with free radicals and the decay of active species. It is concluded that TPI has the potential to improve combustion efficiency compared to traditional spark ignition for wide-ranging applications to engine technology. |
