Fuel effects on PAH formation, toxicity and regulated pollutants: Detailed comparison of biodiesel blends with propanol, butanol and pentanol

Abstract

Blends of biodiesel and high-carbon alcohols have the potential to increase the rate of biofuel use in diesel engines, while reducing harmful and toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Since biodiesel and alcohols do not contain aromatic ingredients in their chemical structures, this study examined biodiesel blends with propanol, n-butanol, and 1-pentanol (5 %, 20 % and 35 % by vol.) and the effects of these aromatic-free fuels on regulated emissions, PAH formation and toxicity as compared to straight diesel fuel in a diesel engine operating at a constant speed and varying engine loads. PAH samples were meticulously processed and extensively analyzed using rigorous analytical chemistry methodology (gas chromatography–mass spectrometry (GC–MS)). Biodiesel and biodiesel-alcohol blends significantly reduced NOx emissions and the level of formation of PAHs and toxicity levels when compared to diesel fuel. Overall, adding 5 % alcohol to biodiesel decreased total PAH emissions. However, with the exception of 20 % propanol, adding 20 % and 35 % alcohol to biodiesel increased total PAH emissions as compared to neat biodiesel. In contrast, all blended fuels resulted in a decrease in the toxicity of PAH compounds (up to 70 %) and the percentage of higher-ring PAHs. Among higher alcohols, propanol blends stood out as reducing PAH formation as compared to n-butanol and pentanol blends. Overall, biodiesel-alcohol blends that emit less carcinogenic pollutants and primarily low-rings PAHs were found to be advantageous for reducing the likelihood of wetstacking in diesel engines under low load or cold operating conditions.