Spark Ignition Discharge Characteristics under Quiescent Conditions and with Convective Flows 2021-01-1157
The arc characteristics and discharge behavior of a representative inductive spark ignition system were characterized with a spark plug calorimeter and a constant volume vessel used to create high-pressure crossflow velocities through the gap of the spark plug. A 14 mm diameter natural gas engine spark plug was used for the measurements. The discharges were into a non-combusting gas, primarily nitrogen.
The spark plug calorimeter was used to determine the electrical-to-thermal energy conversion in the spark gap under quiescent conditions, while the constant volume vessel was used to study ignition arc structure in convective crossflows and imaged with a high-speed camera. Topics included the effect of crossflow velocity, pressure (up to 20 bar at 300 K), and gap distance on breakdown voltage, arc duration and delivered electrical energy. Also of interest was the amount of remaining electrical energy on the coil versus spark duration in a cross flow. Resistance of the arc plasma during the discharge was correlated with arc length and the delivered electrical energy was compared with that dissipated in the internal resistance of the spark plug. The relationship between arc stretch and arc width was studied, as well. The post-breakdown arc voltage and current were correlated with images of the convected plasma arc to elucidate features associated with short-circuiting and restrikes. The relationships among spark duration, arc length and gap flow velocity were also considered. An interesting finding was that the shortened spark duration under high crossflow velocity was due to the more rapid depletion of the electrical energy stored in the secondary side of the inductive ignition circuit rather than to arc instabilities associated with the disturbance of the arc by the flow.