PRESSURE AND CONCENTRATION DEPENDENCES OF THE AUTOIGNITION TEMPERATURE FOR NORMAL-BUTANE PLUS AIR MIXTURES IN A CLOSED VESSEL

The conditions at which autoignition occurs in lean premixed n-butane + air mixtures over the composition range 0.2%-2.5% n-butane by volume (0.06 < phi < 0.66) were investigated experimentally. Total reactant pressure from 0.1 to 0.6 MPa (1-6 atm) were studied in a spherical, stainless-steel, closed vessel (0.5 dm(3)). There is a critical transition from nonignition to ignition, at pressures above 0.1 MPa, as the mixture is enriched in the vicinity of 1% fuel vapor by volume. There is also a region of multiplicity, which exhibits three critical temperatures at a given composition. Chemical analyses of the molecular products of low-temperature combustion are presented. The analyses show that partially oxygenated components, including many o-heterocyclic compounds, are important products of the lean combustion of butane at temperatures up to 800 K. The critical conditions for autoignition are discussed with regard to industrial ignition hazards, especially in the context of the ''autoignition temperature'' of alkanes given by ASTM or BS tests. The differences between the behavior of n-butane and the higher n-alkanes are explained. The experimental results are also used as a basis for testing a reduced kinetic model to represent the oxidation and autoignition of n-butane or other alkanes.