Characteristics of a Two-Stroke Opposed-Piston Compression-Ignition Engine Operating at High Boost

Abstract

The paper describes an experimental investigation arising out of theoretical work by one of the authors (1)†, of the thermodynamic performance of a production opposed-piston compression-ignition engine under conditions of very high boost. By operating the engine with substantial internal cooling in the form of excess scavenge air, b.m.e.p.'s of the order of 230 lbf/in2-at a boost pressure ratio of 3/1 were achieved without imposing excessive thermal or mechanical loading on the engine, and at very high brake thermal efficiencies, exceeding 40 per cent in several instances. The primary independent operating variables were: boost pressure ratio, trapped air/fuel ratio, scavenge ratio, engine speed and simulated compressor efficiency. Very satisfactory agreement with predicted performance figures was obtained and, in addition, a promising correlation of aggregate heat transfer from the engine cylinders with the above operating variables has been devised. The investigation is to be regarded as preliminary to a differential compound engine project, based on theoretical performance predictions by one of the authors (2), in which the engine is merely part of a power unit comprising, in addition, compressors, turbines and differential gearing.