Experimental and theoretical investigation of the combustion characteristics of di-tert-butyl peroxide

Di-tert butyl peroxide is a commonly used cetane booster. It is a potential methyl radical source and therefore suited as a precursor for the investigation of elementary reactions including methyl radicals. In the present study, an independent approach of theory and pyrolysis experiments was used to determine the reaction rate constants for the most important DTBP-dissociation reactions which are the DTBP dissociation into two tert-butoxy (R1) and the subsequential β-scission (R2) to acetone and methyl. In the experimental part a Rapid Compression Machine (RCM) and a Shock Tube (ST) were used to measure pyrolysis times (PTs) and ignition delay times (IDTs) over a temperature range from 540 K to 650 K at pressures of 10 bar, 20 bar and 30 bar with different bath gases in airlike diluted atmospheres. The theoretical investigations considered the O–O dissociation of DTBP and the subsequent β-scission of tert-butoxy to acetone and methyl, treated via Transition State Theory (TST) and Phase Space Theory (PST) and at the DLPNO-CCSD(T)//DSDPBEP86 level of theory. The O–O dissociation rate constants were determined by experiments to k R1 = 2.941 · 10 15 · exp ( − 36672 cal · mol − 1 / ( R · T ) ) · s − 1 and the subsequent β-scission reaction rates can be expressed by k R2 = 5.077 · 10 13 · T 0.223 · exp ( − 11383 cal · mol − 1 / ( R · T ) ) · s − 1 . The experimentally determined rate coefficients of R1 are within the assumed uncertainty of the theoretically obtained reaction constants, which was estimated to be ± 1 kcal mol − 1 in the calculated energy barrier. In this work, a comparison of TST and PST-based rate coefficient showed the limits of TST for this kind of dissociation reactions and the predictivity of PST was proven. Additional, a comprehensive study of the oxidation of the DTBP products was carried out to outline the need for more research for key reactions of the methyl and acetone sub mechanisms.