Hydroperoxides with zero, one, two or more carbonyl groups formed during the oxidation of n-dodecane

Experimental investigations and kinetic interpretation indicate the presenc e of several peroxidic species during the oxidation of n-dodecane. The oxid ation was performed either in the gaseous phase in a flow system, or with a liquid/gas interaction in a bulb, because in many combustion processes liq uid and gas coexist during preignition. The different peroxides were identi fied by mass spectrometry. Simple hydroperoxides with two oxygen atoms per molecule were observed at relatively low temperatures above 370 K with liqu id and gas present. Ketohydroperoxides with three oxygen atoms per molecule s are formed at similar to 500 K. Di-, and even tri, ketohydroperoxides wit h four or five oxygen atoms per molecule are also present under these exper imental conditions at 518 K. Their formation is explained by isomerization reactions of alkoxy radicals OR-2HO bearing a carbonyl group; these stem fr om the decomposition of carbonyl-hydroperoxides. Depending on the experimen tal conditions, the nature of the hydroperoxides is different and the respe ctive reactions of these species should be introduced in low temperature ox idation mechanisms. These reaction schemes should include the isomerization of peroxy radicals RO2 and of ketoalkoxy radicals OR-2HO, leading to the f ormation of peroxides with several carbonyl groups. (C) 2001 by The Combust ion Institute.