Mechanism of the Acetylene—Oxygen Reaction in Shock Waves

Abstract

The oxidation of acetylene has been studied using sufficiently high gas densities and concentrations of inert gas to keep the reaction isothermal and reduce boundary-layer effects. The induction periods and exponential time constants of the oxidation have been measured using the observations of: (a) chemiluminescence and gas conductivity in incident and in reflected shock waves, and (b) total ionization and product formation using a time-of-flight mass spectrometer in reflected shock waves. The results are internally consistent, and the time constants τ are best represented by the following equation: log10(τ[O2])=−11.29+17 000/4.58Tin units of seconds·moles/liter. Induction periods are about eight times longer. The following reaction mechanism is most consistent with the data: H+O2=OH+Ok1=1/(4τionization[O2]),O+C2H2=OH+C2Hk2,OH+C2H2=H2O+C2Hk3,C2H+O2=2CO+Hk4,C2H+O2=CO2+CHk5. Reaction (1) is rate-controlling, the above-defined value of k1 agreeing well with the work of others. The time constants τ for CO, CO2, and H2O are identical, indicating that they are all formed in the branching chain reaction, but those of ionization and luminescence are half as large. Diacetylene formation is observed in acetylene-rich mixtures. Experiments with added CO indicate that Reaction (5) is initially the main source of CO2. The reactionC2H+O=CH(A2Δ)+CO k6explains the observed chemiluminescence well. Experiments with the mass spectrometer show that C3H3+ is the first ion observed. Other experiments suggest that the simple reaction CH(A2Δ)+C2H2=C3H3++e— k7 is not responsible for the ionization. Other possible mechanisms for the formation of C3H3+ are discussed.

Reaction of Atomic Oxygen with Acetylene. II. Chemi-Ionization and Chemiluminescence

“…However, the reaction C 2 H + 0 -> CH (A 2A) + CO (E) has received some support,7 9 The present paper reports some results which pertain to the mechanism of chemi-ionization and chemiluminescence and which were obtained from a study of the reaction of atomic oxygen with acetylene in a moderately fast flow system, Chemi-ions were observed with a ToOFo mass spectrometer. The rate of ion formation and the absolute intensity of chemiluminescent radiation were also measured.…”

Investigation of the kinetics of OH∗ and CH∗ chemiluminescence in hydrocarbon oxidation behind reflected shock waves

“…They pointed out that reaction (R5) plays a minor role for CH * formation with a contribution less than 10 %. Glass et al [34] rejected the relevance of reaction (R5) as dominating pathway and introduced the reaction of ethynyl (C 2 H) radicals with atomic oxygen. Also Brennen and Carrington [35] and Grebe and Homann [23] privileged the following reaction as the main channel:…”

Shock-Tube Study of Cr* Chemiluminescence During the Induction Period of the C2H2–O2 Reaction

“…During the induction period of a chain branching reaction all the main chain carriers grow exponentially with the same growth constant (4,6). If a side reaction, for example chemiluminescence and chemi-ionization in the C2H2-0, reaction, occurs between two chain carriers, products from this reaction grow according to exp @at), where a is the chain branching constant.…”

“…If a side reaction, for example chemiluminescence and chemi-ionization in the C2H2-0, reaction, occurs between two chain carriers, products from this reaction grow according to exp @at), where a is the chain branching constant. In general, the exponential growth constant, E*, of a, particular phenomenon is related to the chain branching constant, a, by where n is the number of chain carriers involved in the reaction leading to the phenomenon (4,5). Since the knowledge of n in eq.…”

“…The early part of the C,H,-0, reaction has been shown to be a highly branched chain reaction (4,5). During the induction period of a chain branching reaction all the main chain carriers grow exponentially with the same growth constant (4,6).…”