抄録
There are strong demands today to further improve the thermal efficiency of internal combustion engines against a backdrop of various environmental issues, including rising carbon dioxide (CO_2) emissions and global warming. One factor that impedes efforts to improve the thermal efficiency of spark ignition engines is the occurrence of knocking. The aim of this study was to elucidate the details of knocking based on spectroscopic measurements and visualization of phenomena in the combustion chamber of a test engine that was operated on two primary reference fuels with different octane ratings (0 MON, 80 MON). The ignition timing was retarded in the experiments to delay the progress of flame propagation, making it easier to capture the behavior of low temperature reactions at the time knocking occurred. Spectroscopic measurements were made at the light emission wavelength and transmitted light wavelength corresponding to those of formaldehyde (HCHO) produced as an intermediate product during a cool flame. Measurements were also made at the light emission wavelength of the OH radical that plays an important role in combustion. As a result, pressure rise by low temperature reaction is considered to be one of the factors affecting knocking intensity.
