Very Lean and Diluted SI Combustion Using a Novel Ignition System with Repetitive Pulse Discharges

A newly developed small-sized IES (inductive energy storage) circuit with semiconductor switch at turn-off action is successfully applied to an ignition system of a small gasoline internal combustion engine. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges is investigated as an alternative to a conventional spark ignition system. The present study focuses on the extension of the operational limits for lean and diluted combustion using the repetitive nanosecond pulse discharges.

First, in order to investigate the flame kernel formation process when the repetitive nanosecond pulse discharges are used, the initial flame kernel is observed using Schlieren photography with a high speed camera. As a result, the flame kernel generated by repetitive pulse discharges is larger than by a conventional ignition system. Then, an application of repetitive nanosecond pulse discharges to a single cylinder SI engine is conducted and the operational limit of lean combustion is investigated. The result shows that the lean limit is extended from 20 to 23 in A/F at IMEP 440 kPa by replacing the ignition system from a conventional one. Also, the diluted limit is investigated. The result shows that the diluted limit is extended from 17.5 % to 22.5 % in EGR ratio at IMEP 630 kPa and that thermal efficiency is improved by 5%. The ignition delay and the combustion duration are decreased and the cycle-to-cycle variation of the ignition timing and IMEP are decreased.