文档介绍：外文翻译原文
Engine performance improved by optimized piston motion
(Otto cycle/optimized heat engines/optimal control)
ABSTRACT The methods of finite-time thermodynamics are used to find the optimal time path of an Otto cycle with friction and heat leakage. Optimality is defined by maximum power-is obtained. The result is an improvement of a conventional near-sinusoidal engine.
Finite-time thermodynamics is an extension of conventional thermodynamics relevant in principle across the entire span of the subject. From the most abstract level to the most applied. The approach is based on the construction of generalized thermodynamic potentials for processes containing time or rate conditions among the constraints on the system and on the determination of optimal paths that yield the extrema corresponding to those generalized potentials.
Heretofore,work on finite-time thermodynamics has concentrated on rather idealized models and on existence theorems, all on the abstract side of the subject. This work is intended as a step connecting the abstract thermodynamic concepts that have emerged in finite-time thermodynamics with the practical, engineering side of the subject, the design principles of a real machine.
In this report, we treat a model of the bustion engine closely related to the ideal Otto cycle but with rate constraints in the form ofthe two major losses found in real engines. We optimize the engine by”controlling”the time dependence of the volume-that is, the piston motion. As a result, without undertaking a detailed engineering study, we are able to understand how the losses are affected by the time path of the piston and to estimate the improvement in efficiency obtainable by optimizing the piston motion.
THE MODEL
Our model is based on the standard four-stroke Otto cycle. This consists of an intake stroke, pression stroke, a power stroke, and an exhaust stroke. Here we briefly describe the basic features of this model and the method used to find the op