High Spatial Resolution Visualization and Spectroscopic Investigation of the Flame Front Propagation in the Combustion Chamber of a Scooter Engine

The match between the increasing performance demands and stringent requirements of emissions and fuel consumption reduction needs a strong evolution in the 2-wheel vehicle technology. In particular many steps forward should be taken for the optimization of modern small motorcycle and scooter at low engine speeds and low temperature start. To this aim, the detailed understandings of thermal and fluid-dynamic phenomena that occur in the combustion chamber are fundamental.

In this work, experimental activities were realized in the combustion chamber of a single-cylinder 4-stroke optical engine. The engine was equipped with a four-valve head of a commercial scooter engine. High spatial resolution imaging was used to follow the flame kernel growth and flame front propagation. Moreover, the effects of an abnormal combustion due to firing of fuel deposition near the intake valves and on the piston surface were investigated. Natural emission spectroscopy in a wide wavelength range from ultraviolet to visible was applied to detect the radical species that marked the normal and abnormal combustion phenomena in the selected operating condition. All the optical measurements were supported by the conventional measurements of the engine parameters.