Add time:09/09/2019         Source:sciencedirect.com

This paper studies the oxidation of n-heptane, iso-octane, ethanol and their mixtures in a pressurized flow reactor, with a focus on the potential relation between the fuels oxidation reactivity and their octane ratings. The flow reactor experiments are conducted at 550–900 K, 10 bar and an equivalence ratio of 0.058. Carbon monoxide is measured as an indicator of the global reactivity. Evident low temperature oxidation and negative temperature coefficient (NTC) behaviors are observed for n-heptane and iso-octane over a similar temperature window (600–800 K). Ethanol, on the other hand, shows negligible reactivity up to 800 K but produces a substantial amount of CO above 850 K indicating significantly higher reactivity than iso-octane. Oxidation of these fuels is then classified into low temperature oxidation (LTO), NTC, intermediate temperature oxidation (ITO), and high temperature oxidation (HTO) regimes.A systematic study is then conducted on primary reference fuels (PRFs) and ethanol/iso-octane mixtures. PRFs show approximately linear blending in terms of CO formation in the LTO, NTC, and ITO regimes, which is consistent with the definition of the octane number scale. In contrast, adding ethanol into iso-octane disproportionally inhibits the CO formation over the same temperature range, with 20 vol% of ethanol completely suppressing the reactivity of iso-octane. Such behavior is also consistent with the synergistic octane blending of the two compounds recently reported [Foong et al. Fuel 115 (2014) 727–739]. These results suggest a potential connection between the oxidation reactivity of these fuels and their octane blending behaviors. Kinetic modeling is conducted using the latest combustion mechanisms for neat compounds and gasoline surrogate. Good agreement in CO formation is observed between the model and experiment for both neat fuels and their mixtures.

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