Air-Standard Modelling for Closed-Cycle Diesel Engines

Abstract

The author posits that a model constructed from ideal processes is the most desirable starting point for analysis of real power machinery, and then presents means of following this concept in the case of a closed-cycle diesel engine. The traditional air-standard limited-pressure cycle is found unsuitable for this application in that it offers only an unrealistic constant-volume cooling as the model for the processes that must occur between cylinder exhaust and cylinder intake. The present paper substitutes isentropic expansion, throttling and constant-pressure cooling as being suitable ideal models for the actual processes. Equations are presented and sample calculations are given for the cylinder-to-cylinder part of an ideal cycle representing a four-stroke naturally aspirated engine. Two alternatives are also discussed via examples: an engine with partial bypassing of untreated exhaust gas to the cylinder intake and a two-stroke engine with blower or compressor driven by an exhaust gas turbine. A closing example is given to demonstrate one way in which the analyses can be used to find the effect of external process states an engine-cycle output.