Soot Emissions of Various Oxygenated Biofuels in Conventional Diesel Combustion and Low-Temperature Combustion Conditions

Abstract

To investigate the effects of oxygenated biofuels on soot formation, oxidation, and distribution, a detailed comparative study using the forward illumination light extinction method was conducted in an optical constant volume combustion chamber. Various ambient temperatures (800 and 1000 K) and ambient oxygen concentrations (21, 16, and 10.5%) were investigated to mimic both conventional diesel combustion and low-temperature combustion conditions. Five oxygenated biofuels were used, including neat soybean biodiesel S100, neat butanol B100, and three alcohol−biodiesel blends that contained by volume 20% ethanol E20S80, 20% butanol B20S80, and 50% butanol B50S50. It is found that the composition of the biofuel has a larger effect on soot suppression efficiency at 800 K ambient temperature than that at 1000 K. Soot distribution is observed at larger distances from the injector, and less soot is located near the wall region with the additional oxygen content of biofuels at 21% ambient oxygen concentration. With a declining oxygen concentration, the soot concentration reduces at 800 K but increases at 1000 K. Soot formed in the spray jet region decreases at lower oxygen concentrations, and soot appears mainly near the wall region. Further, the soot distribution is more dispersed over a wider region at lower oxygen concentrations. B100 has shorter ignition delays at 10.5% oxygen concentration than B50S50 and S100 fuels, despite the fact that it has a lower cetane number. Therefore, the conventional correlation between ignition delay and cetane number does not hold for neat butanol at low oxygen concentrations. Soot concentrations are dramatically increased for soybean biodiesel from 800 to 1000 K at 10.5% oxygen, while such increases are not found for B50S50 and B100 fuels, indicating that proper choosing of the fuel will be very important to the high efficiency and clean low-temperature combustion.

Impacts of acetone on the spray combustion of Acetone–Butanol–Ethanol (ABE)-Diesel blends under low ambient temperature

“…The natural flame luminosity is an important parameter as it is an indicator of soot formation [1,4,31,35]. It can be seen that the natural luminosity first appears at the region between the injector tip and the chamber wall.…”

“…Butanol has recently been identified as a feasible alternative to diesel fuel in CI engines [1][2][3][4]. Acetone-Butanol-Ethanol (ABE) fermentation is one of the major methods used to produce bio-butanol.…”

“…Studies [1,4,14,15] have also shown superior clean combustion capabilities of alcohol fuels, relative to diesel and biodiesel, particularly under LTC conditions.…”

Experimental investigation of particle emissions under different EGR ratios on a diesel engine fueled by blends of diesel/gasoline/n-butanol

“…In recent years, butanol has been extensively investigated and regarded as a promising prospective additive for diesel and gasoline [10][11][12][13][14][15]. Compared with methanol and ethanol, n-butanol is more easily soluble in diesel fuel and hydrophilic, which decreases the risks of corrosion of carbon steels.…”

Impact of higher n-butanol addition on combustion and performance of GDI engine in stoichiometric combustion

“…Investigation of n-butanol usage as the engine fuel has been conducted for some researchers. In diesel engines, especially, the research groups, represented by Yao et al [10,11], Liu et al [12,13], Rakopoulos et al [14,15], and the author [16,17] have investigated the characteristics of n-butanol blended with diesel combusted in diesel engines. On conventional port fuel injection (PFI) spark ignition (SI) engines, on the other hand, the majority of studies on n-butanol have been performed either as pure fuel or blend fuel due to its high octane number.…”