Effects of Ethanol, n-Butanol, and n-Pentanol Addition to Diesel Fuel on Combustion and Emission Characteristics in a Common-Rail Diesel Engine with Exhaust-Gas Recirculation

Abstract

The study aims to evaluate the combined effects of alcohols as additives to diesel and exhaust-gas recirculation (EGR) on combustion and emission characteristics of a common-rail diesel engine. Tested fuels were prepared with 25% ethanol, 25% n-butanol, 25% n-pentanol, and 50% n-pentanol by volume, referred to as E25, B25, P25, and P50, respectively. The effects of different alcohol contents and a wide range of EGR ratios on combustion and emissions characteristics, especially particulate emissions, were investigated. The results demonstrate that with EGR ratios increasing, for each fuel, the peak of cylinder pressure decreases and the peak of heat release rate increases, both of which are delayed. The premixed combustion phase of alcohol/diesel blends is larger than that of pure diesel. Furthermore, alcohol contents and EGR ratios have obvious effects on indicated thermal efficiency (ITE). ITE increases after the addition of alcohol to diesel, but falls as EGR increases. Regarding emissions, the particulate number concentration of each fuel shows a unimodal distribution versus particulate size. At low and medium EGR ratio situation (<40%), the peak particulate number concentration increases quickly and the particulate size grows larger with increased EGR ratios. The total particulate number concentrations (TPNCs) of alcohol/diesel blends are much lower than pure diesel except for n-pentanol/diesel blends. But when EGR ratio continually increases, the peaks of particulate number concentration and the particulate size decrease. For almost all EGR ratios, the TPNCs of P25 and P50 are much higher than those of E25 and B25.