Low pressure cooled exhaust gas recirculation (EGR) to suppress engine knocking is increasingly being used to downsize engines and increase the compression ratio to improve thermal efficiency.This study aims to develop an ignition system to extend the EGR limit and EGR operation area. The ignition system must be improved to enhance ignitability of a mixture of fuel and air. In this paper, we focus on ignition energy of the ignition coil and summarize experimental results on a test dyno obtained by using reinforced conventional ignition coil on the basis of ignition energy and engine speed.As engine speed (mixture flow velocity between ignition plug electrode-gap) and EGR ratio were increased, the secondary energy requirement of the ignition coil was increased. This increase was considered to be caused by an increase of mixture flow velocity at the plug gap and a decrease of laminar flame velocity as EGR ratio increased.An increase of the secondary energy of ignition coil extended the EGR limit. Fuel economy was improved more by the increase of EGR than by the lower EGR limit condition. On the other hand, electric power consumption by reinforced ignition was increased for the engine system. Therefore, ignition energy needs to be optimized in accordance with engine operation.