Impact of n-butanol substitution in ethylene on soot yields in laminar diffusion flames at pressures 3 to 10 bar

Abstract

Bioalcohols are perceived to be cleaner burning fuels and generally are assumed to be soot suppressants when blended with hydrocarbon fuels. Butanol isomers display some superior physical and chemical properties as compared to methanol and ethanol, and could be blended with hydrocarbon based transportation fuels without substantial modifications in engine hardware. However, the controversy in the literature about the influence of lower alcohols on soot when blended with hydrocarbons at various proportions has not been resolved yet. Further, there is a lack of information on the dependence of soot production on pressure obtained from tractable flames of butanol-hydrocarbon blends. Such benchmark information on the behaviour of soot characteristics at elevated pressures would be helpful to facilitate a better interpretation of the soot emissions from engines fuelled with butanol-hydrocarbon blends as well as providing data that could be used for numerical simulation efforts. Soot volume fractions and temperature fields of laminar coflow diffusion flames of a nitrogen-diluted ethylene base fuel and of the base fuel doped with 10% n-butanol were measured at operating pressures of 3, 5, 8 and 10 bar in a high-pressure chamber with optical access. Radially resolved temperatures and soot volume fractions were inferred from spectrally resolved radiation emitted by soot from the flames, stabilized on a 3 mm diameter burner, in which carbon and nitrogen mass flow rates in the fuel stream were kept constant. Maximum soot yield decreased by about 25% to 45% when 10% of the carbon in the fuel stream is provided by n-butanol throughout the pressure range; although local enhancements in soot production were observed at 3 bar. However, increases in local soot production disappeared when the pressure is increased to 8 and 10 bar. Current results were compared to ethanol substitution in the same base fuel under identical conditions.