Non-intrusive optical measurements were carried out in the combustion chamber of an optical direct injection spark ignition (DISI) engine in order to characterize the chemical and physical processes involved using bio-ethanol fuel with respect to commercial gasoline. In particular, an optical four strokes small single cylinder engine for two wheels vehicles was used. It was equipped with an elongated piston with a wide sapphire window in the head and a quartz cylinder. Two different engine conditions based on different engine speed and load were investigated considering the effect of injection pressure. Exhaust emissions and engine performances were assessed during the imaging and spectral measurements in order to investigate the spray characteristics and flame propagation with high spatial and temporal resolution. The simultaneous application of high injection pressures and bio-ethanol showed to be a valid answer to pollutants reduction demand without worsening the performances in DISI engines, even if it needs a careful optimization of the injection system in order to better exploit the ethanol's properties. (c) 2012 Elsevier Ltd. All rights reserved.