Novel experimental investigation of spontaneous ignition of gaseous hydrocarbons

Abstract

Studies of spontaneous ignition of gases under rapid compression^1–3 are directed mainly towards understanding ‘knock’ in spark-ignition engines and the duration of ignition delays in diesels. The relevance to engine combustion lies in the ability to investigate the effects of fuel structure on the development of spontaneous ignition (arising either in different isomers of a hydrocarbon or due to reaction of mixtures of different hydrocarbons), while avoiding complicating practical features such as droplet evaporation, induction and exhaust of the charge, reciprocating piston motion and cycle-to-cycle variations. We report here a novel development, in which a variable-speed impeller in the combustion chamber of a rapid compression apparatus is used, first, to bring about spatial uniformity of temperature and concentration throughout the ignition delay period and, second, to enhance the rate of heat dissipation by successive increases in the speed of rotation. We show that, at given conditions for rapid compression, spontaneous ignition ceases to be possible beyond a limiting rotor speed.