Diesel blends with high concentrations of biodiesel and n-butanol: Effects on regulated pollutants and polycyclic aromatic hydrocarbons

Abstract

Despite advances in alternative energy production (including electric vehicles and hydrogen fuel cells), fossil fuels remain ubiquitous and an ongoing threat to the environment. Alternative biofuels such as biodiesel and n-butanol have garnered substantial attention in recent years as additives to fossil diesel as a means to control emissions such as nitrous oxides (NOx) and carbon monoxide (CO). In addition, as biodiesel and alcohols do not contain aromatic hydrocarbons in their chemical structures, they provide potential additional advantages for reducing toxic emissions, including polycyclic aromatic hydrocarbons (PAHs); however, this is often only demonstrated for relatively low blend ratios (<20 %). In this study, the effects of neat diesel, waste oil biodiesel, and n-butanol blends on engine function, regulated, and unregulated emissions were investigated for blends containing 50/50 vol% diesel/biodiesel (D50B50), 50/25/25 vol% diesel/biodiesel/n-butanol (D50B25Bu25), and 50/50 vol% diesel/n-butanol (D50Bu50), in addition to neat standard road diesel (D100) and waste oil derived biodiesel (B100). In these blends NOx was reduced by up to 28.1 % relative to D100 for loads above idle, while increasing exhaust gas temperatures up to 33.5 % and increasing unburned hydrocarbons (HC) and CO by up to 84.2 % and 93.8 %, respectively. Measured against neat diesel, biodiesel and the diesel-biodiesel-butanol blend reduced PAH toxicity by up to 46.4 %, while diesel-biodiesel and diesel-butanol blends showed an increase up to 14.3% and 504%, respectively, due to higher concentrations of 5-ring PAHs. It has been concluded that in addition to fuel aromaticity, other factors such as fuel properties affecting the diesel combustion process (i.e. cetane number), can cause PAH formation.