An Opposed Piston Rapid Compression Machine for Preflame Reaction Studies

Abstract

Mixtures of fuel and air ignite spontaneously if exposed to sufficiently high temperatures. Such ignition is not an instantaneous event, and there is always a delay of chemical origin between the establishment of the particular conditions of temperature and pressure and the rapid, exothermic chemical reactions that constitute ignition. This delay is of outstanding importance in any fuel application in which spontaneous ignition plays a part. It is determined by the progress of the near-isothermal chemical processes that precede ignition, and these processes therefore merit continued study. This paper describes the development of an experimental technique which allows these studies to be extended to much higher pressures than those accessible in glass vessels, while retaining many of the advantages of laboratory vessel experiments. This technique is centred on a rapid compression machine of novel design which is used to heat and compress fuel/air mixtures to conditions near those in a knocking engine. After this compression process, which occupies a few milliseconds only, the hot, high pressure charge is held at constant volume while thermochemical, spectroscopic or analytical observations are made. The principal new developments in the machine are the use of twin opposed pistons for compression with an associated hydraulic synchronizing system and a precisely triggered valve that enables rapid quenching and sampling of the reacting mixture to be made at an appropriate stage of reaction.