Cold idle vs hot idle: Gaseous and particulate emissions using a third-generation oxygenated biofuel

Engine idling is a significant contributor to vehicle emissions, however, it is often unaccounted for. Presented in this study is a comprehensive analysis of gaseous and particulate emissions during cold idle compared to hot idle operations. Fuels used in this study were B20 (20 %) and B10 (10 %) (%v/v) blends of di-octyl phthalate (a third-generation microalgae-based biofuel) and ultra-low sulphur diesel (B00), used as a reference fuel. Compared to cold idle operation, hydrocarbon (HC) emissions during hot idle showed marginal variation (±10 %) using blended fuels, and a significant increase (+55 %) using B00. Compared to cold idle operation, hot idle showed increased oxides of nitrogen (NOx) emissions, using all fuels (with a more significant increase shown using B00). During cold idle, particle concentrations (PNT) were 50–65 % higher using the blended fuels, compared to B00; however, during hot idle, the (PNT) using the blended fuels were one order of magnitude lower than B00. During cold idle operation, the average particle count mean diameter (CMD) in the Lower Aitken and Aitken modes was 5–10 % and 20–30 % higher using blended fuels, compared to B00, respectively. Higher CMD with the blended fuels during the cold idle operation caused a higher percentage increase in the particle mass (PMT), compared to B00. Sub-23 particles (<23 nm) were observed during cold and hot idle operations, using all fuels.