Self-heating in the H2+ O2 reaction in the vicinity of the second explosion limit

Abstract

The existence of self-heating accompanying hydrogen oxidation in closed vessels in the vicinity of the P–T_a second explosion limit has been demonstrated experimentally, apparently for the first time. Direct measurements of the extents of temperature rises in equimolar (H₂+ O₂) and stoichiometric (2H₂+ O₂) mixtures have been made using a fine-wire thermocouple-junction placed at the centre of the reaction vessel. Two cylindrical quartz vessels have been used; their volumes were 330 and 100 cm³, respectively.

Self-heating during slow reaction close to the second limit is negligible only at the lowest temperatures; it becomes significant as the vessel temperature is increased. The temperature rise exceeds 3 K at locations in the P–T_a diagram close to where the second and third limits coalesce. Still greater extents of self-heating are measured in the slow reaction zone at pressures higher than those at the second limit.

This study offers the first experimental test of the numerical predictions using chain-thermal theory: encouraging agreement is found.