This paper examines the influence of water on burned gases, with the object, above all, of obtaining a deeper knowledge of the processes which take place in the combustion chamber of a diesel engine alimented with water-in-fuel emulsions. This study, of a theoretical nature, utilizes a simplified model which consents to consider at the end of combustion, the composition, temperature, internal energy and nitric oxides calculated by taking into account the kinetic reaction. Although the model does not consider the real behaviour of the combustion chamber, but refers to a constant volume process far homogeneous mixtures, the results obtained furnish general.indications which can be used far comparative purposes, also of aid in the experimental interpretation of the phenomena involved.