The present paper discusses the results obtained by experimental investigations of the diffusion-controlled flame near the valves due to fuel film deposition in a single cylinder, ported fuel injection (PFI), four-stroke spark-ignition (SI) engine with a four-valve production head. The engine was equipped with a transparent combustion chamber with a wide quartz window in the bottom. Optical techniques, based on 2D-digital imaging and natural emission spectroscopy, were used to follow the flame propagation and the chemical species involved in the fuel deposition burning near the valves. Two-colour pyrometry was applied to evaluate the flame temperature and soot concentration. Finally, exhaust particle size distributions were measured and correlated with the fuel deposition burning. The effects of different operating conditions in terms of speed, spark timings, and injection phasing were tested. Moreover, the effect of multi-component fuel was investigated by the comparison between commercial gasoline and pure iso-octane. (C) 2008 Elsevier Ltd. All rights reserved.