High Energy Ignition Strategies for Diluted Mixtures via a Three-Pole Igniter 2016-01-2175
A three-pole spark igniter, with the concept to broaden the ignition area, is employed in this paper to investigate the effect of spark discharge strategies on the early ignition burning process. The prototyped three-pole igniter has three independent spark gaps arranged in a triangular pattern with a circumradius of 2.3 mm. Direct-capacitor discharge techniques, utilizing close-coupled capacitors parallel to the spark gap, are applied on the three-pole igniter to enhance either the transient spark power or the overall energy. In particular, the simultaneous discharge of high energy plasma on three spark gaps can produce a surface-like ignition process which intensifies the plasma-flame interaction, thereby producing a rapid flame kernel development. The ignition strategies are evaluated in both constant volume combustion vessels and a modified single-cylinder metal engine. In the results, for both the lambda sweep and the CO2 dilution tests performed in the constant volume combustion vessels, three-pole ignition exhibits significantly faster burning, compared to the single-pole ignition, which is indicated by the shortened time to 5% mass fraction burnt (MFB) and the time to 50% MFB. The ignition improvement by the three-pole arrangement is consistently observed for various energy levels and sparking modes. A preliminary test on a modified single-cylinder research engine, with a relatively low spark energy level, shows that the three-pole ignition can noticeably improve the combustion phasing control for a lean burn operation.