The Oxidation of Propane at Low and Transition Temperatures

Abstract

An experimental study of the oxidation of propane in the temperature range 563-743 K was carried out using a static reactor. The oxidation mechanism was found to undergo a transition from a low temperature reaction regime ( T < 600 K) t o that of a n intermediate temperature regime (T > 650 K) separated by a region of negative temperature coefficient (600-650 K). In the lower temperature regime alkylperoxy radicals are formed and become the dominant radical species. These can react in several ways, the most important of which leads to the formation of hydroperoxides. Hydroperoxides were determined to be the main chain branching intermediates responsible for the acceleration of the reaction and for the formation of cool flames. At the intermediate temperatures hydroperoxyl radicals are dominant and lead to hydrogen peroxide. which is the main branching intermediate in this regime. These conclusions are based in large measure upon the hydrocarbon products formed which consist mainly of oxygenated species at the lower temperatures and lower alkanes and alkenes at the intermediate temperatures. The negative temperature coefficient and the change in mechanism are due to the competition between reactions involving the addition of OZ to the alkyl radical forming the alkylperoxy radical and reactions involving the abstraction of hydrogen from the alkyl radical by Oz to form the conjugate alkene and the hydroperoxyl radical. The effect of increasing the reaction vessel surface-tovolume ratio was t o enhance heterogeneous termination, resulting in longer reaction times. Comparison of the reaction products from vessels with different surface-to-volume ratios showed there t o be n o significant effect of surface on the main reaction paths of the mechanism. Some aspects of the mechanism at these temperatures are compared to those in the high temperature regime (T > 1000 K).

Studies of a fuel-rich propane flame with photoionization mass spectrometry

“…Key undetected flame radicals include OH, C 3 H 7 , HCO, C 2 H 5 , and HO 2 . Hydrogen peroxide, H 2 O 2 , was also not observed, despite the prominent role assigned to it in propane flame chemistry [5][6][7][8][9][10]. This result is in contrast to other studies we have completed for fuel-rich H 2 /O 2 /Ar flames in which H 2 O 2 , formed in the primary flame zone, was observed to persist into the post-flame zone.…”

“…Propane is a simple hydrocarbon that exemplifies reaction characteristics of practical higher-hydrocarbon fuels. Current kinetic models rely on measurements of ignition delay in shock tubes, laminar flame speeds, and quartz microprobe sampling of species from jet-stirred flow reactors, turbulent flow reactors, diffusion flames, pressurized flow reactors, and constant volume reaction vessels [5][6][7][8][9][10]. Homann et al [11] reported the only previous study of a low-pressure premixed laminar propane flame using molecular beam mass spectrometry (MBMS).…”

“…A significant benefit is the ability to precisely tailor the photon energy to minimize interferences caused by ionization of multiple species of the same or nearly equal masses, and by dissociative ionization of species of higher mass than that of the target molecule. Detailed modeling of key kinetic reaction mechanisms in propane combustion, coupled with a variety of experimental measurements [5][6][7][8][9][10], has long been pursued in an effort to understand the rich chemistry of C 3 hydrocarbons. Propane is a simple hydrocarbon that exemplifies reaction characteristics of practical higher-hydrocarbon fuels.…”

Comprehensive kinetic model for the low temperature oxidation of hydrocarbons

“…The model predictions for propane oxidation are in good agreement with the experimental data (Wilk et al, 1986) and do a good job of reproducing the transition from dumped cool flames to slow combustion, as is clearly shown in Figure 6. Good agreement with experimental results has also been obtained in terms of species evolution, as reported in Figure 7 .…”

“…Propane, propene, and n-butane oxidation have been studied by Wilk et al (Wilk et al, 1986(Wilk et al, , 1987(Wilk et al, , 1995 in a conventional nonisothermal batch SR. The system consists of a cylindrical Pyrex vessel (volume 1,395 cm3, diameter 10 cm, surface-to-volume ratio 0.5 cm-') located inside a temperature-controlled compartment.. Reactants are first premixed and then rapidly admitted to the preheated, evacuated reaction vessel.…”