Abstract
The progress of flame propagation and the autoignition behavior of the end gas at the time of knocking in a spark-ignition engine were examined on the basis of emission and absorption spectroscopic measurements and visualizations obtained by high-speed photography. The test fuels used were a 30 RON fuel and n-heptane. Emission and absorption spectroscopic techniques were applied to investigate the behavior of formaldehyde (HCHO) and OH radicals in the interval from the occurrence of a cool flame to autoignition. The results showed the occurrence of cool-flame reactions along with light absorption and faint light emission ascribable to HCHO in the end gas prior to knocking.
