Wave Action in Diffusers for Exhaust-Pipe Systems, with Special Reference to the Scavenging of Two-Stroke Engines

The work described was carried out in the Mechanical Engineering Department of Birmingham University and is an extension of the investigation into air flow in a naturally aspirated two-stroke engine described in an earlier paper (Wallace and Nassif 1954)‡. In that paper the scavenging process of an unblown, opposed-piston engine with simple parallel-pipe exhaust and inlet systems was analysed, and the results were compared with experimental observations. Only a brief reference was made to the very marked increase in air flow resulting from incorporation of a diffuser in the exhaust system.The present paper describes first a theoretical investigation of wave effects in the exhaust system using: (1) The small-wave theory; (2) The method of characteristics; (3) An approximate analytical treatment designed to give better accuracy than (1), but to avoid the extremely laborious computations associated with (2); and, secondly, an experimental programme comprising: (1) Air-flow tests with various diffuser arrange...