Investigation on flame developments in a SI engine with tumble flow using OH PLIF

The present study is aimed at exploring the spatial and temporal development of the flame kernel using OH planar laser-induced fluorescence (PLIF) in a single cylinder optical SI engine with a gasoline surrogate fuel. A tumble enhancing intake port is used for the sake of improvement of ignition and flame propagation. The engine speed was set to 2000 rpm through the experiments. Equivalence ratio is changed from 1.0 to 0.6. With decrease of equivalence ratio, ignition timing is changed to be earlier for appropriate combustion. From the preliminary measurement using particle image velocimetry (PIV), it is found that the cycle-cycle variations of main stream direction of tumble flow at the ignition point are prone to be large in approaching to top dead center in the compression stroke, which significantly affects characteristics of flame and in-cylinder pressure developments. From results of OH PLIF in different crank angle degrees (CAD) after ignition, characteristics of flame behavior are investigated with considering temporal evolution of in-cylinder pressure and characteristics of discharge path. For the stoichiometric condition, overall flame locations are fluctuated by variations of main flow direction, while nevertheless the pressure evolves properly due to fast flame propagation. For the lean conditions, initial stage of flame kernel development has great influence on the completeness of whole combustion.