In recent years, from a viewpoint of global warming and energy issues, improving vehicle fuel economy to reduce CO2 emission is required. One of the improvement ways is to enhance the engine thermal efficiency, and for that, automakers have been developing the technologies of high compression ratio, dilute combustion such as exhaust gas recirculation (EGR) and lean combustion. Since the excessive dilute combustion causes the failure of flame propagation, combustion promotion by intensifying in-cylinder turbulence has been indispensable. However, instability of flame formation by the gas flow fluctuation between combustion cycles is becoming an issue. Therefore, achieving stable flame formation and propagation under a high dilute condition is important technology. DENSO CORP. has developed the new ignition technology to be able to form flame surely under variable gas flow velocity conditions. The system consists of not only ignition coil but also electronic drive unit for discharge control. This paper reveals the most suitable discharge specification for stable high dilute combustion based on the mechanism of flame formation in various engine conditions, and then shows the expanding effects of dilute combustion limit compared with conventional ignition technology. The engine tests were conducted in various engine conditions. In the high gas flow condition, keeping the high discharge current achieved stable flame formation because of suppressing blow-off of discharge channel, and in the low gas flow condition, expanding discharge duration and so discharge channel improved dilute combustion limit because of heat loss reduction of discharge and also initial flame. As the result, the new ignition technology could achieve a superior engine thermal efficiency. In addition, it realized energy saving of ignition system.