Shock-Tube Study of Chain Branching during the Induction Period of the Hydrogen—Oxygen Reaction

Abstract

The growth of ``blue continuum'' emission has been measured during the induction period of the reaction of H₂ (0.5%, 1.5%, and 5%)–CO (3.3% and 33%)–O₂ (0.5%)–Ar mixtures between 1100° and 1700°K. For sensitivity, the reacting gas behind reflected shock waves was viewed axially through a large end plate window and lens. The observed intensity I, representing the integral of I′ (x)dx between reflected shock front and end plate, exhibited 2 to 3 decades of exponential growth, I = I₀ exp(αt). α is related to the branching chain kinetics of H₂–O₂ combustion through the proportionality of I′ (x) to the product [CO][O]. α was found to be satisfactorily proportional to density and independent of [CO], and its dependence upon [O₂] and [H₂] was analyzed to yield rate coefficients for $$\mathrm{H}+{\mathrm{O}}_2\to {\displaystyle {lim}^{k_1}}\mathrm{OH}+\mathrm{O}$$ and $$\mathrm{O}+{\mathrm{H}}_2\to {\displaystyle {lim}^{k_2}}\mathrm{OH}+\mathrm{H}$$ between 1290° and 1667°K. These are represented by $$k_1{\text{=10}}^{\text{10.89}}\hspace{0.17em}\exp \text{\hspace{0.17em}(−14.45\hspace{0.17em}}\mathrm{kcal}\mathrm{/RT)\hspace{0.17em}}\mathrm{liter}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$$ (±10%) over our range, and $$k_2{\text{=10}}^{\text{10.51}}\hspace{0.17em}\exp \text{\hspace{0.17em}(−10.0\hspace{0.17em}}\mathrm{kcal}\mathrm{/RT)\hspace{0.17em}}\mathrm{liter}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$$ from combination of our mean result with literature data at 400°K.