Study of three valves command laws of the expansion cylinder of a hot air engine

Abstract

The family of hot air engines with external heat input is divided in two subgroups: the Stirling engines, invented in 1816, have no valves whereas Ericsson engines, invented in 1833, have valves in order to isolate the cylinders. The valves give some advantages to the Ericsson engine. Amongst them, the most important one is that the heat exchangers are not to be considered as unswept dead volumes whereas the Stirling engine designer is faced to the difficult compromise between heat exchanger transfer area maximization and heat exchanger volume minimization. However, the distribution system of the Ericsson engine introduces some complexity and a non-negligible mechanical energy consumption in order to actuate them. An original and very simple system called "bash-valve" is proposed to provide answers to the difficulties related to the distribution system of the Ericsson engine. The "bash-valve" technology has been used in steam piston engines and pneumatic piston engines. In this system, the piston itself actuates the opening of the valves when being around the top dead center. When its moves to the bottom dead center, the piston loses contact with the valves and it closes under the effect of the return spring. Three different valves command laws of the expansion cylinder of the proposed hot air engine are studied. A comparison between energy performance of the engine with the expansion cylinder equipped with two kinds of bash valve technology and the energy performance of the expansion cylinder of an incomplete expansion Joule Ericsson cycle engine is presented as well as their influence on the design of the system.