Evaluation of variable mass moment of inertia of the piston–crank mechanism of an internal combustion engine

Abstract

The current paper presents an original method for evaluating the variable mass moment of inertia of the piston–crank mechanism of an internal combustion engine based on the principle of kinetic energy equality of the real mechanism and its reduced model. The method has been developed to evaluate the variable mass moment of inertia of a 12-cylinder V-engine having a piston–crank mechanism with main and auxiliary connecting rods. In order to study the influence of the piston–crank mechanism configuration on mass moment of inertia variability, the procedure has been also applied on virtual ‘shortened’ variants: 2-cylinder and 6-cylinder V-engines with main and auxiliary connecting rods, and a 6-cylinder in-line engine with simple piston–crank mechanism. The results are compared with values obtained using the usual simple method for determining the approximate constant mass moment of inertia based on Huygens–Steiner theorem. It is shown that there is negligible difference between the constant value obtained by the simple method and the mean value of variable mass moment of inertia evaluated using the proposed model. Variability of mass moment of inertia is relatively small for a large number of cylinders, but it rises with cylinder number reduction. The presented method with appropriate modifications may be applied to any piston–crank mechanism arrangement.