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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.

A surface reaction occurs at a certain surface temperature when the catalyst is heated up in a reactive mixture. If homogeneous ignition does not occur, a steady state is observed because the heat produced by the surface reaction is balanced with the heat loss caused by convection, conduction and radiation. The steady temperature is defined as the temperature at the steady state. This paper treats the pressure effects on the surface reaction. Hydrogen and oxygen are used as reactants and nitrogen as an inert gas. The height, width and length of the combustion chamber are 76 mm, 140 mm and 140 mm, respectively. A spherical Pt catalyst sample of 1.5 mm in diameter is sustained in the chamber with two wires of 0.1 mm in diameter. As results, there is a maximum steady temperature at a certain equivalence ratio (ERmax) and ERmax increases with total pressure. At the steady state, it can be approximated that the heat release is evaluated by the mass transfer which includes the effect of natural convection. The experimental results could be explained qualitatively by the approximation.

A surface reaction occurs on a catalyst surface when the catalyst sample is heated up to a certain temperature in a reactive mixture. After the surface reaction occurs, a steady state is observed without energy supply because the heat produced by the surface reaction is balanced with the heat loss caused by convection, conduction and radiation. The heat release of the surface reaction can be evaluated by the surface temperature of the catalyst sample at the steady state.This paper treats the effects of the equivalence ratio (ER) and the dilution ratio (DR) of the reactive mixture on the surface reaction. Hydrogen and oxygen are used as reactive mixture and nitrogen as inert gas. The height, width and length of the combustion chamber are 76mm, 140mm and 140mm, respectively. A spherical Pt catalyst sample of 1.5mm in diameter is sustained in the chamber with two wires of 0.1 mm in diameter. The chamber is filled with a hydrogen-oxygen-nitrogen mixture at the atmospheric pressure and the room temperature. The surface temperature is measured with a thermocouple. As the results, the heat produced by the surface reaction decreases with increasing dilution ratio, and hydrogen is adsorbed more easily compared with oxygen.