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To investigate the flame characteristics under a high efficiency spark ignition engine condition, a direct numerical simulation (DNS) of forced ignition of premixed mixtures in a constant volume vessel with a tumble flow has been performed for a lean Toluene Reference Fuel (TRF)-air mixture at a high exhaust gas recirculation (EGR) rate at high pressure. After a certain time, separated reaction region is observed. It is found that flame characteristics just after the ignition region are close to the corresponding laminar flame and flame characteristics of separated reaction region are different from laminar flame.

To adhere to stringent environmental regulations, SI (spark ignition) engines are required to achieve higher thermal efficiency. In recent years, EGR (exhaust gas recirculation) systems and lean-burn operation has been recognized as key technologies. Under such operating conditions, reducing CCV (cycle-to-cycle variation) in combustion is critical to the enhancement of overall engine performance. Flow-field CCV is one of the considerable factors affecting combustion in engines. Conventionally, in research on flow fields in SI engines, the ensemble average is used to separate the measured velocity field into a mean component and a fluctuation component, the latter of which contains a CCV component and a turbulent component. To extract the CCV of the flow field, previous studies employed spatial filter, temporal filter, and POD (proper orthogonal decomposition) methods.