The characteristics of the inhibition of the H2+02 reaction by methane are shown to differ markedly from those found with ethane and the hjgher hydrocarbons. In particular, the continuous decrease in explosion pressure down to the junction of the first and second limits, found when increasing amounts of ethane or propane are added, is now replaced by a sudden and complete suppression of explosion at a critical methane concentration with little decrease in the explosion pressure. A more marked effect of hydrogen mole fraction, and a significant diameter effect without an accompanying surface effect, have also been found with methane. Four types of mechanism have been examined : (a) a mechanism retaining the isothermal nature of the limit and assuming a direct inhibition by methane, (b) a thermal explosion, with direct inhibition by methane, (c) an isothermal limit, with inhibition due to formaldehyde which has reached an equilibrium concentration, (d) inhibition due to formaldehyde which has not reached a stationary concentration when the critical condition for explosion is reached. It is shown that the first three types of mechanism cannot explain the experimental results, and that the inhibition shows a number of features consistent with the thermal limit required by the fourth type of mechanism.
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