Explosions of coal-gas and air

Abstract

The experiments here described consist in an investigation into the propagation of flame through a mixture of coal-gas and air contained in a closed vessel and ignited at one point by an electric spark. A continuous record is taken of the variation of resistance of fine platinum wires immersed in the gas, at different points; and at the same time and on the same revolving drum the pressure is recorded. The arrival of flame at any wire is marked by a sharp rise in its resistance. Thus the progress of the flame can be traced. Moreover, the rate of rise of temperature of the wire after the flame has reached it is (after certain corrections have been applied) a measure of the velocity with which the gases round about it combine. In this manner it has been possible to settle in the case of certain mixtures, at any rate, the question of “after-burning,” which has long been a matter of controversy in the theory of the gas-engine, and to determine approximately the specific heat of the mixture of CO 2 , H 2 O, and inert gases which are the products of the combustion. Incidentally it has been necessary to find what relation the temperature of a fine platinum wire immersed in the heated gas bears to that of the gas. Burstall, who has measured the temperature in a gas-engine cylinder by means of platinum wires, did not fully investigate this point, and his results are, in consequence, open to doubt. Before proceeding to a detailed account of the apparatus and records obtained it will be convenient to state shortly the principal conclusions reached. The experiments were all made on mixtures of air and Cambridge coal-gas having an average “higher” calorific value of 680 British Thermal Units per cubic foot at 0°C. and 760 mm. The composition of the gas is given in an appendix. The mixture was fired at atmospheric pressure in a vessel of dumpy cylindrical form and of a capacity of 6⋅2 cubic feet, which is shown in section in fig. 1. The combustion was started by an electric spark at the centre of the vessel.