Hot surface ignition of methane-air mixtures has been experimentally studied in normal gravity and microgravity. The primary aim of this research is to explain the effects of natural convection and catalytic reaction on the hot surface ignition in a closed vessel. The hot surfaces used are platinum wire for catalyst and nickel wire for non-catalyst. In order to define the initial condition and make the analysis simple, the following control unit was developed; which heats the wire to the setting temperature in a very short time, and maintains the wire temperature constant until ignition. From experimental results, ignition temperatures with platinum wire are higher than those with nickel wire by the catalytic inhibition of ignition due to the reactant depletion on the surface of the wire. Ignition temperatures with platinum wire are highest near the stoichiometric mixture ratio and decrease with equivalence ratio depart from stoichiometric mixture ratio, while those with nickel wire increase with equivalence ratio. Ignition temperatures in normal gravity are higher than those in microgravity. Natural convection supplies reactants to the platinum wire surface, and therefore reactants are consumed because of promoting catalytic reaction in normal gravity.
