Abstract
The study deals with the light absorption and emission behavior in the preflame reaction interval before hot flame reactions (1-3) . Emission spectroscopy was used to measure the behavior of HCHO, OH radicals and HCO during a progression from normal combustion to knocking operation. Absorption spectroscopic was measured in the same way. Those radicals are known to play a role in the combustion reaction of hydrocarbon fuel. Radical behavior in preflame reaction was examined on the basis of simultaneous measurements, the light emission behavior measured for the three radicals by emission spectroscopy was introduced into a polychromator and the absorption behavior measured by absorption spectroscopy was introduced into a monochromator for each species individually. When n-heptane were used as test fuel, it was observed that radical behavior differed between normal combustion and knocking operation. The measurements obtained for HCHO showed an increase in emission intensity in the early period of the preflame reactions under normal combustion, followed by a decline in intensity. These tendencies are thought to correspond to the passage and degeneracy of a cool flame. The OH radicals and HCO also show similar light emission behavior. Under knocking operation induced by an overheated cylinder head, the maximum emission intensity decreased.