A single stroke compression expansion apparatus is used to investigate the flame propagation under SI engine conditions. The gas is ignited by a row of electrodes located along the center line of the cylinder head of a square cross section combustion chamber. This leads to a cylindrical flame geometry which allows spatially resolved measurements of the light emission. The quasi two dimensional flame geometry allows the determination of the origin of the light emission and the distinction between the flame zone and the regions of burnt and unburnt gas.The correlation of the light emission of the CH band at 431.5 nm with the mass burning rate is used to derive information about the mass burning rate distribution from CH band emission measurements. In the selected region of the CH band emission a considerable intensity of light emission emanating from the burnt hot gas region is also observed. From this part the emission originating from the flame zone is separated. It correlates well with the mass burning rate. By measuring the spatial and temporal distribution of this quantity the local flame speed relative to the unburned gas along the flame surface can be determined.