Anomalous behavior during explosions of CH(4) in oxygen-enriched air

Explosion tests were performed for CH 4/O 2/N 2 mixtures in a non-adiabatic 5L cylindrical vessel. Experiments were run for mixtures with stoichiometric CH 4/O 2 ratio, changing the oxygen air enrichment factor, E=O 2/(O 2+N 2), from 0.21 (air) to 1 (pure oxygen). Oscillating pressure time histories with over-adiabatic peaks (up to 240bar) have been measured. The oscillating behaviors can be attributed to the occurrence of cycles of condensation and vaporization of the water produced during combustion. Such cycles culminate in the rapid phase transition of the condensed water, leading to the over-adiabatic pressure peaks.