Formation of polycyclic aromatic hydrocarbons in a diesel engine fueled with diesel and biodiesel containing low concentrations of n-propanol/n-butanol/n-pentanol

Diesel engines remain indispensable in energy production and transportation, necessitating effective strategies to mitigate toxic unregulated emissions. Despite extensive research on oxygenated fuels, the influence of higher alcohol molecular structure on polycyclic aromatic hydrocarbon (PAH) formation and toxicity remains poorly understood. This study systematically investigates the effects of 7.5% (v/v) n-propanol (C3), n-butanol (C4), and n-pentanol (C5) blending with diesel (D100) and biodiesel (B100) on total PAH emissions, relative distribution, and toxicity-weighted (BaPeq) emissions under identical operating conditions using gas chromatography–mass spectrometry (GC–MS) analysis. The addition of higher alcohol markedly reduced total PAHs and suppressed the formation of higher-ring carcinogenic species. Among the tested blends, n-propanol consistently delivered the greatest reduction in both total PAH concentration and toxicity. This superior performance is attributed to structure-dependent combustion effects, including enhanced charge homogeneity, moderated local temperature evolution, and suppression of aromatic growth pathways. Overall, these findings provide a basis for the rational design of oxygenated fuel mixtures to reduce unregulated emissions associated with toxicity in future diesel combustion systems.