Technical Paper
Friction Losses of a Novel Prototype Variable Expansion-Ratio, Spark Ignition, Four-Stroke Engine
1997-08-06
972659
The novel engine concept represents an alternative approach to achieve the benefits ideally associated with so-called Otto-Atkinson engines in which, in earlier experimental units, the induction stroke was effectively shortened, at part load, by early, or late, inlet valve closure. In the new engine the need for variable valve timing is avoided because a specially designed mechanism shortens the induction/compression strokes and lengthens the expansion/exhaust strokes for part-load operation while maintaining constant the engine compression ratio. A concern with such an engine relates to the inherent friction loss. Accordingly, a theoretical study of the mechanical loss due to the new mechanism was conducted using a commercially available code. It was found that the friction loss of the new engine configuration was approximately 10% lower than that of an otherwise comparable conventional four-stroke engine.