Explosion Limits

Attention has already been directed to the influence of inert gases upon the rate of travel of the explosion-wave through a combustible mixture. In general the velocity falls until a certain dilution is reached at and beyond which no explosion takes place. This is explained by the fact that the heat generated by union of the combustible gases is largely absorbed in raising the temperature of the indifferent gas instead of being employed in propagating the explosion. As is to be anticipated, therefore, by raising the initial temperature of the gases prior to firing, the dilution with inert gas may be carried further than in the cold. In other words, the lower limit of explosion of the combustible gas is depressed.

Teclu gives the following explosion limits for mixtures of combustible gases and air, the method of exploding consisting in firing by an electric spark:

Explosion limits in Air

Gas.	Lower Limit. Per cent, by Volume.	Upper Limit. Per cent, by Volume.
Hydrogen	9.73-9.96	62.75-63.58
Coal-gas	4.36-4.82	23.35-23.63
Methane	3.20-3.67	7.46-7.88
Acetylene	1.53-1.77	57.95-58.65

Closely connected with this is the problem of the completeness of combustion of gaseous mixtures when diluted with inert gases. This has been investigated by Parker3, who finds that the effect of increase of initial temperature is much less in the case of hydrogen mixtures than with methane or carbon monoxide mixtures. The lower limit of hydrogen is much the same whether mixed with air or oxygen, but for carbon monoxide, methane, and coal-gas, the lower limits in oxygen are greater than in air, probably on account of the greater specific heat of oxygen.