Dependence of stoichiometric ratio on the composition of the working mixture

Abstract

n order to use the well-known Stechkin’s expression   in relation to different fuels, it is necessary to substitute into it the values of the lowest working calorific value of  and the stoichiometric ratio of   characteristic for each specific fuel. The corresponding values depend on the chemical composition of the fuel and are given in the reference literature. The calculation of the stoichiometric ratio is carried out according to oxidation formulas, assuming that the volume fraction of oxygen in the air is 21% and the mass fraction is 23%. However, in the cylinders of reciprocating internal combustion engines, the fuel is burned not in the air, but in its mixture with combustion products, which should lead to a deviation in the value of the oxygen fraction from the above-mentioned values and, consequently, to an increase in the stoichiometric ratio of  .

In this regard, the task is to take into account the effect of the content of neutral combustion products in the working mixture on the value of the stoichiometric ratio. To solve it, a thermodynamic analysis of the ratios of partial volumes of the components of the working mixture was used.

The article presents the dependencies obtained as a result of the analysis to determine the stoichiometric ratio depending on the fraction of neutral combustion products in the working mixture.