Discharge of Exhaust Gases in Two-Stroke Engines

Abstract

The paper points out that the two-stroke engine still has a field of great importance, i.e. the compression-ignition engine, and that, although the two-stroke cycle has been known for so long, the theory of the discharge of exhaust gases from the cylinder is still in doubt, and some of the generally accepted assumptions have been challenged in recent years, in particular by Kadenacy. A description is given of apparatus built at the Engineering Laboratories, University of Cambridge, to simulate the discharge portion of the cycle only. This apparatus utilizes the gases nitrogen and hydrogen under compression, these being respectively denser and less dense than exhaust gases. Experiments were made to ascertain whether the older theories were valid, and to investigate the claims of Kadenacy of supersonic discharge and resultant vacuum pressures in the cylinder. These tests demonstrated that the older theories, based on the assumption of steady flow and Bernoulli's theory, were substantiated, provided that modifications were made to the index of expansion and the coefficient of discharge. Finally, a simplified system is derived for the calculation of the size of exhaust ports or valves, and this system is applied to a practical case.