Knocking diagnostics in the combustion chamber of boosted port fuel injection spark ignition optical engine

High spatial resolution optical techniques have been used to get information about the timing and the location of knocking and about the chemical species involved in this phenomenon. The experiments were realised in the combustion chamber of a boosted single-cylinder spark ignition port-fuel injection optical engine fuelled with commercial gasoline. Engine conditions with different levels of knock were considered from the borderline case onto standard knocking and heavy knocking. Cycle-resolved digital imaging was used to follow the combustion and the flame propagation in normal combustion and knocking conditions. Moreover, the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface were investigated. The knocking influence on the flame front propagation and combustion speed was investigated following the time evolution of the mean flame radius in the different engine conditions. The appearance of the autoignition centres in the end gas during the knock was evaluated in terms of timing, location and frequency of occurrence. Finally, UV-visible natural emission spectroscopy was applied to detect radical species that marked the knock. HCO and OH were identified as markers of the knocking onset and OH of its intensity