Characteristics of n-butane weak flames at elevated pressures in a micro flow reactor with a controlled temperature profile

Abstract

The very first successful experiments at elevated pressures up to 1.2MPa by an “in-pressure-chamber”-type micro flow reactor with a controlled temperature profile are demonstrated. n-Butane was applied to the micro flow reactor and the ignition characteristics at pressures of 0.1–1.2MPa were investigated by observing weak flames. Among three kinds of separated weak flames which can be observed by the present reactor, the blue flame was only observed at pressures higher than 0.2MPa and the cool flame was only observed at pressures higher than 0.3MPa. This interprets the multi-stage oxidation for n-butane was confirmed experimentally and computationally. The positions of the blue and cool flames shifted towards the lower temperature side along with the increase of pressure in the experiment. Computation results reproduced the experimental tendency of the blue and cool flames. The wall temperature value at the cool flame position in the experiment agreed with that in the computation at all pressures studied, and that at 1.0MPa agreed with the compressed temperature at which the cool flame was observed in the rapid compression machine at a compression pressure of 10bar. The computational weak flame structure at 0.1MPa was compared with that of 1.0MPa. High-temperature oxidation is important at 0.1MPa while low temperature oxidation is important at high pressures. At 1.0MPa, most of the fuel is consumed at the cool flame. Separated cool flames were found at 1.2MPa and four-stage oxidation was produced in the computation. Rate of production analysis indicated that the first cool flame was formed by fuel oxidation through low-temperature oxidation while the second one was formed by reaction of peroxyl radicals with H2O2.