Combustion and emissions of isomeric butanol/gasoline surrogates blends on an optical GDI engine

The combination of distinctive physicochemical properties of biofuels and recent engine technologies offer benefits in terms of efficiency improvement and emissions reduction. The recent development in butanol bio-based production pathways encourage researchers to study their combustion characteristics. This paper experimentally evaluates the combustion and emissions of a gasoline direct injection (GDI) engine fueled with the butanol isomer/gasoline surrogate blends, in which primary reference fuel (PRF) and toluene primary reference fuel (TPRF) are selected as the gasoline surrogates, respectively. The flame propagation behaviors, in-cylinder pressure, apparent heat release rate, along with PN emissions from this optical GDI engine are discussed. First, butanol addition to the gasoline surrogates is found to slow down flame propagation, reduce peak cylinder pressure and heat release rate, and extend ignition delay and combustion duration. Further, among the four butanol isomers, n-butanol and tert-butanol are the most and least reactive fuels, respectively, whereas iso-butanol and sec-butanol show reactivities in between, as supported by the measured flame propagation and pressure traces, calculated heat release rates, as well as time scales describing the combustion progress, e.g. ignition delay and combustion duration. Finally, butanol addition reduces the PN emissions from the GDI engine, and the PN emissions reduction capacity of the four butanol isomers ranks as sec-butanol > iso-butanol > n-butanol > tert-butanol. Also, compared to the PRF/butanol blends, the PN emissions are reduced to a less extent when butanol is blended with TPRF.