Flame Diagnostics in the Combustion Chamber of Boosted PFI SI Engine

The growing demands on fuel economy and always stricter limitations on pollutant emissions has increased the interest in the ignition phenomena to guarantee successful flame development for all the spark ignition (SI) engine operating conditions. The initial size and the growth of the flame have a strong influence on the further development of the combustion process. In particular, for the new FIAT generation of turbocharged SI engines, the first times of spark ignition combustion are not yet fully understood. This is mainly due to the missing knowledge concerning the detailed physical and chemical processes taking place during the all set of the flame propagation. These processes often occur simultaneously, making difficult the interpretation of measurements.

In the present paper, flame dynamic was followed by UV-visible emission imaging in an optical SI engine. The measurements provided detailed information on flame formation and propagation with respect to the level of turbulence in the combustion chamber.

The experiments were realized in an optically accessible single cylinder boosted PFI SI engine. The elongated piston of the engine was flat and included a transparent quartz window to allow optical measurements through a 45° mirror located in the bottom of the engine. Different boost pressures were considered. All tests were realized by commercial gasoline.