The dissociation of carbon dioxide at high temperatures

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The power of an internal combustion engine is greatest when operating with a “rich” mixture, that is to say, with a mixture which contains more fuel than is necessary for complete combustion. Similarly, it is found that if mixtures of carbon monoxide and air in varying proportions are exploded in a closed bomb at constant initial temperature and pressure, the explosion pressure is greatest when the ratio CO/O 2 is greater than 2. These phenomena are known to be connected with the dissociation of carbon dioxide at high temperatures, for if there were no dissociation we should expect the explosion pressure to be greatest when CO/O 2 = 2. No attention appears, however, to have been paid to the position of the maximum. It can be shown in the following way that there is a very simple relation between the composition of the mixture giving maximum pressure on explosion, and the dissociation of carbon dioxide at the maximum explosion temperature. Let the initial composition be represented by the expression 2 (1 + a ) CO + O 2 + b N 2 (Total mols = 3 + 2 a + b ), and let P i , T i represent the initial pressure and temperature; P e the maximum pressure observed after explosion, and T e the corresponding maximum temperature.