Operating Characteristics of Compound Engine Schemes for Traction Purposes Based on Opposed Piston Two-Stroke Engines and Differential Gearing

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Abstract
In an earlier paper (1)†, the performance characteristics of combinations of two-stroke compression ignition engines with compressors and turbines were analysed under the headings (1) Turbosupercharged engines with mechanically driven scavenge blowers, (2) Gas generators, (3) Compound engines with fixed ratio geared connection between engine., compressor, turbine and output shaft. The object of the present paper is to extend the method of analysis outlined in the previous paper to cover various compound engine arrangements with differential rather than fixed ratio gear connection between the members of the aggregate. It is shown that such units meet to a very high degree the specific requirements of the traction application, namely (1) High unit power achieved by the use of high boost pressures, (2) Torque-speed characteristics approaching the ideal hyperbolic law, and permitting drastic simplification of the external transmission system, (3) Good part-load efficiency—superior to both the turbocharged and the gas generator engine—made possible by free power flow between the members of the aggregate, (4) High degree of engine-assisted braking, and (5) Good response to sudden changes in load demand. Two arrangements, both meeting these requirements to a high degree, are considered. These units constitute a significant advance over existing traction prime movers.

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