Experiments on knocking and abnormal combustion through optical diagnostics in a boosted spark ignition port fuel injection engine

In this paper, flame front propagation during normal and abnormal combustion was investigated. Cycle-resolved flame emission imaging was applied in the combustion chamber of a port fuel injection-boosted spark ignition engine. The engine was fueled with a mixture of 90% iso-octane and 10% n-heptane by volume (Primary Reference Fuel 90: PRF90) and commercial gasoline. The combustion process was monitored from the flame kernel formation until the exhaust valves opened. Different phenomena associated with abnormal combustion were analyzed, including the fuel deposition burning. Moreover, the ignition surfaces and end-gas auto-ignitions were investigated in terms of timing, location and frequency of occurrence. The analysis was performed by considering different knocking intensities for both the selected fuels.