Two-Stroke Engines-Models for Charge Renovation

The behaviour of fluid flow in piston-ported crankcase-scavenged two-stroke engines is evaluated. Two complementary models of charge renovation are developed: The first model, named the “geometric submodel”, relates the equivalency bases between real designs and sketches of the ducts for the flowing fluid. The other one, named the “analytic submodel”, employs the unidimensional flow theory to study the characteristics variables in the reference sections of the ducts.

An instantaneous Admission Coefficient concept is established and plotted versus crantangle. A Global Admission Coefficient is calculated and its variation versus rpm is obtained.

The models are used to determinate the optimum engine geometry for a given Admission Coefficient.