The effects of pressure, temperature, and concentration on the reactivity of alkanes: Experiments and modeling in a rapid compression machine

Abstract

Experiments in a rapid compression machine have examined the influences of variations in pressure, temperature, and equivalence ratio on the au toigni tion of n-pentane.Equivalence ratios included values from 0.5 to ' 2.0, compressed gas initial temperatures were varied between 675K and 980K, and compresed gas initial pressures varied from 8 to 20 bar. Numerical simulations of the same experiments were carried out using a detailed chemical kinetic reaction mechanism.The results are interpreted in terms of a low temperature oxidation mechanism involving addition of molecular oxygen to alkyl and hydroperoxyalkyl radicals. Idealized calculations are reported which identify the major reaction paths at each temperature. Results indicate that in most cases, the reactive gases experience a two-stage autoigni tion. The first stage follows a low temperature alkylperoxy radical isomerization pathway that is effectively quenched when the temperature reaches a level where dissociation reactions of alkylperoxy and hydroperoxyalkylperoxy radicals are more rapid than the reverse addition steps. The second stage is controlled by the onset of dissociation of hydrogen peroxide. Results also show that in some cases, the first stage ignition takes place during the compression stroke in the rapid compression machine, making the interpretation of the experiments somewhat more complex than generally assumed. At the highest compression temperatures achieved, little or no first stage ignition is observed.

Ignition of isomers of pentane: An experimental and kinetic modeling study

“…Temperatures computed in this manner represent spatial averages because, due primarily to heat losses to the combustion chamber walls, different regions in the compressed gas have local temperatures that are different from the averaged temperature. Autoignition delay times computed from this average temperature can therefore produce results either longer or even shorter than the experimentally determined values [12].…”

“…There have been recent modeling studies of n-pentane [4,12,20], neopentane (2,2-dimethyl propane) [20][21][22], and isopentane (2-methyl butane) [21]. These mechanisms are refined continually, but the three mechanisms used here are at the same level and detail as that reported [21] for neopentane.…”

“…Hydrocarbon oxidation studies in the RCM have been summarized [10,11], and many classes of fuels have been studied. Detailed kinetic modeling is another tool to study autoignition in the RCM [4,12]. The present work was intended to determine experimentally the influence of variations in fuel molecular structure on autoignition and to use a kinetic model to understand those variations.…”

“…The present work was intended to determine experimentally the influence of variations in fuel molecular structure on autoignition and to use a kinetic model to understand those variations. This study is unique because although other studies have addressed effects of variations in pressure and equivalence ratio [12], this work addresses effects of variations in fuel molecular structure for all isomers of a single fuel, pentane, in an RCM. The three isomers of pentane possess many of the structural elements that determine such autoignition characteristics as octane number and variability in cool flame production.…”

Demonstration of a free-piston rapid compression facility for the study of high temperature combustion phenomena

“…In support of their experimental work, this group studied the development of the temperature field [9], performed computational fluid dynamics (CFD) modeling [10], and performed extensive kinetics modeling of reaction chemistry [11,2].…”