Spectra produced by shock waves, flames and detonations

Abstract

Emission spectra excited in various gases, including fuel and fuel+argon mixtures, by strong shock waves from a bursting diaphragm are compared with those given by flames and by spark-ignited and shock-ignited detonations. Shocks through hydrocarbon or hydrocarbon+argon mixtures, without oxygen, give carbon formation and C 2 emission but not CH. Formaldehyde, ether, alcohols, ethyl nitrate, carbon tetrachloride and chloroform have also been studied. Carbon monoxide+argon mixtures give strong C 2 but no CO bands; hydrogen or oxygen only slightly quench this C2, but mixed hydrogen and oxygen quench it strongly. Reactions involving C 2 and CH are discussed. In detonations, OH is very strong, and C 2 and CH are weak compared with burner flames. Time records, using a photomultiplier and oscillograph, indicate that C 2 emission comes from the reaction zone of the detonation, but OH and the continuous spectrum are emitted mainly by the hot gases behind the front. The relation of the results to the propagation mechanism is briefly discussed. Shock-excited spectra resemble those produced by flames rather than those from discharge tubes, and this appears to be a promising technique for studying fundamental processes in flames.