MODELING OF THE GAS-PHASE OXIDATION OF n-DECANE FROM 550 TO 1600 K

摘要

To improve the performances of diesel engines and to reduce the emission of pollutants at their outlet, it is necessary to be able to model the combustion and the oxidation of higher alkanes. Up to now, only a few detailed kinetic mechanisms were written for modeling the combustion of alkanes higher than n-heptane and iso-octane and even fewer for modeling their oxidation at low temperature in the cool flame region or in the negative temperature coefficient (NTC) regime. This paper presents a modeling study of the oxidation and combustion of n-decane in a range of temperatures, from 550 to 1600 K, aiming at reproducing experiments performed in a jet-stirred reactor and in a premixed laminar flame. The study covered an important part of the wide range of temperatures that is observed in engines. It is worth noting that n-decane is actually present in diesel fuel. Detailed kinetic mechanisms have been automatically generated by using the computer package EXGAS developed in our laboratory. The predictions of the mechanisms were compared to the experimental results without any adjustment of kinetic data. The mechanism used for simulation at low temperature included 7920 reactions. A satisfactory agreement was obtained for the two kinds of experimental apparatus, both for the consumption of reactants and for the formation of most products. In the flame, the formation of pollutants, such as unsaturated compounds, was well reproduced. In the perfectly stirred reactor, a flow rate (flux) analysis at 650 K in the cool flame region showed a scheme of reaction close to that of n-heptane. Nevertheless, the higher reactivity of n-decane compared with that of lower linear alkanes such as n-heptane seems to be due not only to faster metathesis reactions favored by additional secondary abstractable atoms of hydrogen, but also to a lower relative flow rate of oxidations giving alkenes and the very unreactive HO_2·radicals. The long linear chain favors internal isomerizations and then reduces the relative flow rates of reactions competing with the addition of oxygen.