Influence of dimethyl ether and diethyl ether addition on the flame structure and pollutant formation in premixed iso-octane flames

While the combustion reactions of many individual fuels in flames have been studied in detail, often providing numerous experimental species profiles in combination with the development and critical testing of kinetic models, similar work on fuel mixtures has remained scarcer, especially for blends of conventional and biogenic fuels. In the present study, we have thus chosen iso-octane, one of the primary reference fuels that determine octane number and knocking tendency of gasoline, as the base fuel, and dimethyl ether (DME) and diethyl ether (DEE) as potentially bio-derived fuel components. Premixed low-pressure flames of iso-octane without and with different amounts of DME or DEE, of up to 50% of the fuel in the mixture, have been investigated systematically to analyze the change of the flame structure and species composition upon blending. All flames were studied at a pressure of 40 mbar (4 kPa) with 50% argon dilution and a cold gas velocity of 60 cm s(-1). The carbon-to-oxygen ratio was fixed at 0.47 while the equivalence ratio changed from 1.47 to 1.84. Up to 70 species in the range of C-0-C-9 were identified and quantified in each flame by electron ionization molecular-beam mass spectrometry (EI-MBMS). Moreover, about 300 experimental species profiles were provided. The aim of this study is thus threefold. First, a new species dataset for a pure iso-octane flame is reported, since speciation data under premixed flame conditions for this fuel is surprisingly scarce. Second, the effects of DME and DEE addition in increasing amounts to the iso-octane base flame are investigated with special attention to the flame structure and pollutant species formation. Third, a joint combustion model for iso-octane, DME, and DEE mixtures consisting of 379 species and 1931 reactions is proposed that was examined against the present data and reference experiments for a larger range of conditions. Key pathways of interesting species, including aldehydes, alkenes, and soot precursors were revealed with the present mixture model. DME and DEE addition were found to have a similar influence on the flame structure of iso-octane, except for some C-2 and C-3 intermediates. The addition of DME as well as of DEE decreases the formation of soot precursors while it enhances the production of formaldehyde. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.