Di-tertiary-butyl Peroxide Decomposition and Combustion with Air: Reaction Mechanism, Ignition, Flame Structures, and Laminar Flame Velocities

Abstract

This study investigates the ignition/combustion of di-tertiary-butyl peroxide (DTBP) over a wide range of fuel/air ratios using numerical flame calculations to gain insight into species profiles and ignition/combustion characteristics of DTBP/air mixtures. The results are flame zone and reaction zone structures as well as the corresponding laminar flame speeds and propagation speeds of reaction zones. Several detailed reaction mechanisms are evaluated in the flame simulations, and sensitivity of the computed results to important reaction steps was evaluated. The ignition of DTBP in the absence of oxygen belongs in the category of thermal runaway because there is no chain branching associated with the early stages of the reaction; i.e., decomposition steps lead to acetone and ethane. In the presence of oxygen, the development of a flame is more complex and exhibits a two-stage ignition, where the first stage, at lower temperatures, involves the thermal decomposition of DTBP to acetone, which further oxidizes to the final combustion products. This second high-temperature ignition process involves chain-branching reactions for the combustion of acetone and ethane and the usual chain-branching reactions of the H2/O2 system. The calculations reproduce this two-stage ignition behavior for fuel-rich flames, and the calculated flame structures reflect the interaction of decomposition of DTBP to acetone and ethane and the subsequent combustion. DTBP has a relatively weak RO–OR bond and readily undergoes dissociation at higher temperatures to two RO• radicals, and it is widely used as a radical source, reaction initiator. Five reaction mechanisms (M1–M5) were employed in this study for analysis of the reaction system, which differ mainly in the reaction rates for the initial DTBE decomposition reaction. When using relative high reaction rates for the initial decomposition reactions (M1 and M2), the flame velocities of DTBP/air mixtures exhibit two maxima over the entire range of the mixture fraction. The first maximum is located at stoichiometric conditions, while the second prevails under fuel-rich conditions. Decelerating the primary decomposition reactions (M3–M5) in favor of the combustion reactions of the DTBP decomposition products shows the second maximum disappearing as result of the relative low propagation speed of the reaction zone. The first maximum is only slightly altered by varying the reaction rates, because the decomposition step of DTBP and the combustion of the primary decomposition products merge at stoichiometric conditions and temperatures are high enough to result in high decomposition rates.