Assessment of carbonyl and PAH emissions in an automotive diesel engine fueled with butanol and renewable diesel fuel blends

Abstract

A comparative experimental study assessing the unregulated emissions of carbonyl compounds, polycyclic aromatic hydrocarbons (PAHs) in solid particle and gaseous phase and the contribution to ozone formation potential, was carried out for an automotive diesel engine operating under two representative urban driving conditions with butanol and renewable diesel. Both renewable fuels were blended with ultra-low sulfur diesel (ULSD) fuel to replace 13% of aromatic compounds in the reference fuel (Butanol at 13%v/v –Bu13- and Renewable diesel –RD- at 13% v/v –RD13-) and in the case of RD, an additional concentration of 20% v/v was tested (RD20). The particle and gas phase sampling procedure for PAHs characterization was carried out without any air dilution. A total of 18 PAHs (16 requested by the US EPA + benzo[e]pyrene and dibenzo[a,l]pyrene which is acknowledged for its significant carcinogenic potential) were determined. Independently of the engine operating mode, Bu13 exhibited the highest carbonyl compound emissions among all tested fuels (M1:18.8 mg/kWh of formaldehyde, M2: 18.2 mg/kWh of acetaldehyde) and the highest ozone formation potential (307 mg O3/kWh). Both RD blends exhibited similar carbonyl emissions (RD13 = 7.0 mg/kWh, RD20 = 8.3 mg/kWh) compared to ULSD (10.2 mg/kWh). Independently of the fuel and engine operating mode, most of the PAHs were present in the gas-phase, with predominance of those between 3 and 4 rings (up to 70%). No trend was observed on PAHs emissions with the addition of butanol or RD to the ULSD. It was observed that some local combustion conditions might increase the emissions of PAHs for both renewable fuels, mainly those of lower molecular weight.