Effect of oxymethylene ether (OME3-5) e-fuel blends on unregulated toxic emissions of carbonyl compounds and polycyclic aromatic hydrocarbons

Oxymethylene ethers (OME_x) are renewable e-fuels synthesized from hydrogen and captured carbon dioxide. These compounds have emerged as promising e-fuels to reduce emissions from diesel engines. This study evaluates the impact of oxymethylene ether blends containing three to five carbon atoms (OME_3-5) on unregulated toxic emissions, focusing on carbonyl compounds and polycyclic aromatic hydrocarbons (PAHs). A Euro 6a diesel engine was tested with 5 %, 10 %, and 15 % OME_3-5 blends (OME5, OME10, and OME15) using the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). Unregulated pollutants were analyzed through a comprehensive sampling methodology upstream of the diesel oxidation catalyst and particulate filter. A total of 16 PAHs and 13 carbonyls were analyzed. The study revealed that OME_3-5 blends reduce carbonyl and PAHs emissions. Formaldehyde and acetaldehyde were identified as dominant carbonyls, with formaldehyde emissions decreasing by 30 % across blends. Carbonyl emission factors ranged from 22.5 ± 3.75 to 45 ± 1.7 mg/km, markedly exceeding gaseous PAHs emissions (∼20 ± 3 to 115 ± 7 μg/km). Gas-phase and particle-bound PAHs exhibited reductions ranging from 35 % to 70 % as the OME_3-5 concentration increased up to 15 %, with significant reductions in high-molecular-weight PAHs. Furthermore, ozone formation potential (OFP) and respiratory activity fraction (RAF) analyses showed the lower atmospheric impact of OME_3-5 blends compared to conventional diesel. These findings underscore the potential of OME_3-5 blends as e-fuel to support sustainable fuel transition.