Effect of $\mathrm{SO}_2$ on the chain reaction of hydrogen oxidation: Intermittent flames

The effect of $\mathrm{SO}_2$ on the chain reaction of hydrogen oxidation in the autoignition region ($T=470-510^\circ$C and $p<200$ torr) is studied. In the absence of $\mathrm{SO}_2$ under flow conditions, the process occurs in a low-temperature flame mode with a characteristic pale blue glow. With the addition of sulfur dioxide, $\mathrm{SO}_2$ is transformed to elemental sulfur and a new phenomenon is observed. At a small contact time (less than $4$–$5$ s), the process enters the mode of intermittent flames. Dependences of the rate and intensity of light flashes on pressure, temperature, and contact time are studied. An interpretation of the observed phenomenon is given.