A detailed chemical kinetic model for oxidation of CH 3 OH at high pressure and intermediate temperatures has been developed and validated experimentally. Ab initio calculations and RRKM analysis were used to obtain rate coefficients for key reactions of CH 2 OH and CH 3 O (dissociation, isomerization, reaction with O 2 ). The experiments, involving CH 3 OH/O 2 mixtures diluted in N 2 , were carried out in a high pressure flow reactor at 600-900 K and 20-100 bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Under the conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, while increasing pressure shifted the ignition temperature towards lower values. Model predictions of the present experimental results, as well as Rapid Compression Machine (RCM) data from the literature, were generally satisfactory. The governing reaction pathways have been outlined based on calculations with the kinetic model. Unlike what has been observed for unsaturated hydrocarbons, the oxidation 2 pathways for CH 3 OH under the investigated conditions were very similar to those prevailing at higher temperatures and lower pressures. At the high pressures, the modeling predictions for onset of reaction were particularly sensitive to the CH 3 OH+HO 2 ⇌CH 2 OH+H 2 O 2 reaction.

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The use of oxygenated compounds as additives to diesel fuels is considered nowadays as a promising alternative for minimizing soot emissions and maybe also NO x under appropriate conditions [1,2]. Classical oxygenated compounds include alcohols and ethers, and among them, ethanol (C 2 H 5 OH) and dimethyl ether (CH 3 OCH 3 , DME) are two of the most popular candidates to be used as additives. The use of ethanol has been extensively studied in the last years and it is already being used in reformulated gasolines, like E85 (85% ethanol and 15% gasoline) [3]. Similarly, DME has received considerable attention because of its high cetane number, vaporization characteristics, low toxicity, and low tendency to produce smoke and volatile organic compounds (VOCs) [4]. Additionally, DME can be produced from renewable materials [5,6].Ethanol and DME have the same molecular formula (C 2 H 6 O) but different structure and functional group, and, as it has been discussed in several previous works (e.g. [7,8]), the oxygen content and the specific structure of the oxygenated compound strongly influence the capacity for pollutant emission minimization. Song et al. [9] concluded that, under the conditions of their modeling study, both DME and ethanol were effective in reducing aromatic species (important soot precursors). However, DME exhibited a greater effectiveness due to its higher enthalpy of formation, which led to a higher final flame temperature and consequently to a decrease in aromatic species production in premixed flames [10], but also because of its structure. For fuel-rich conditions, the reaction flux analysis conducted by these authors [9] determined that reactions involving DME convert only approximately 15% of its carbon to C 2 -species (key species in the production of aromatic species), whereas reactions of ethanol convert approximately 35% of its carbon to C 2 -species. AbstractDimethyl ether (DME) is a promising diesel fuel additive for reducing soot and NO x emissions, because of its interesting properties and the possibility of a renewable production. An experimental and modeling study of the oxidation of acetylene (C 2 H 2 , considered as an important soot precursor) and DME mixtures has been performed under well-controlled flow reactor conditions. The influence of temperature, air excess ratio (λ) and presence of NO on the oxidation process has been analyzed. Under fuel-rich conditions, the presence of DME in these mixtures modifies the radical pool delaying the acetylene consumption. C 2 H 2 and DME, and the radicals generated in their conversion, interact with NO achieving different levels of NO concentration diminution depending upon the operating conditions. Under fuel-lean conditions, the presence of DME in the mixtures increases the NO diminution, whereas for the other values of λ considered, the maximum NO decrease reached is lower than that obtained in the case of pure acetylene.