Optical characterization of the combustion process in a 4-stroke engine for 2-wheel vehicle

The match among the increasing performance demands and the stringent requirements of emissions and the fuel consumption reduction needs a strong evolution in the two-wheel vehicle technology. In particular, many steps forward should be taken for the optimization of modern small otorcycles and scooters at low engine speeds and high loads. To this aim, detailed understanding of thermo-fluid dynamic phenomena that occur in the combustion chamber is fundamental. In this work, low-cost solutions are proposed to optimize ported fuel injection spark ignition (PFI SI) engines for two-wheel vehicles. The solutions are based on the change of phasing and on the splitting of the fuel injection in the intake manifold. The experimental activities were carried out in the combustion chamber of a single-cylinder 4-stroke optical engine fuelled with European commercial gasoline. The engine was equipped with a four-valve head of a commercial scooter engine. High spatial resolution cycle-resolved digital imaging was used to characterise the flame propagation. It was investigated the presence of diffusion-controlled flames near the valves and on the cylinder walls that induced the formation of unburned hydrocarbons and soot particles. The in-cylinder optical investigations were correlated with engine performance and exhaust emissions.