A Continuous Discharge Ignition System for EGR Limit Extension in SI Engines

A novel continuous inductive discharge ignition system has been developed that allows for variable duration ignition events in SI engines. The system uses a dual-coil design, where two coils are connected by a diode, combined with the multi-striking coil concept, to generate a continuous current flow through the spark plug. The current level and duration can be regulated by controlling the number of re-strikes that each coil performs or the energy density the primary coils are charged to. Compared to other extended duration systems, this system allows for fairly high current levels during the entire discharge event while avoiding the extremely high discharge levels associated with other, shorter duration, high energy ignition systems (e. g. the plasma jet [1, (2) under bar], railplug [(3) under bar] or laser ignition systems [(4) under bar, (5) under bar, (6) under bar, (7) under bar, (8) under bar]. Tests on a single cylinder of a 4-cylinder engine indicated that the addition of the continuous discharge mode resulted in a larger improvement in burn rate and stability than was achieved by either one coil in multi-strike mode or both coils in multi-strike mode with simultaneous discharge. The improvement in burn rate and stability translated into improved fuel consumption, particularly at low specific power levels and at high engine speeds. Finally, the improvement in EGR tolerance at low load conditions is seen as an important enabler for high dilution engines, as the requirement for engine stability during throttle tip-out is an important limiting factor in the ultimate EGR levels targeted by engine designers.