Detailed assessment of exhaust emissions in a diesel engine running with low-carbon fuels via FTIR spectroscopy

Low-carbon fuels have been proposed as alternatives that can help with the transition to a sustainable and decarbonized transport sector. This study examines the potential of four different fuel blends with different renewable content to reduce pollutant emissions by evaluating both regulated and unregulated emissions produced by their combustion in a light-duty compression ignition engine. The study distinguishes between two measurement conditions: drop-in and optimized calibration. The drop-in calibration represents the operation of low-carbon fuels using baseline injection settings, while the optimized calibration involves a specific approach to reduce nitrogen oxide emissions. Unregulated emissions were measured using a Fourier Transform Infrared analyzer, which recorded various substances, including aldehydes (acetaldehyde, formaldehyde), saturated hydrocarbons (ethylene, propylene, 1,3 butadiene, and isobutylene), unsaturated hydrocarbons (methane and ethane), aromatics (benzene and toluene), and the greenhouse gas nitrous oxide (N2O). Results indicated that aldehyde production is not affected at low-load operation for fuels with higher oxygen content, but instead, the use of diesel from vegetable origin in the fuel blend could lead to slight increases in this species. On the other hand, the production of saturated hydrocarbons was impacted by the cylinder temperature and combustion duration, being the oxygenated fuels with longer combustion durations at low-load, which reported reductions, but at mid-load, this effect is mitigated. In addition, the production of aromatics and unsaturated hydrocarbon emissions were assessed as soot precursors. The production rate of these species was higher when the calibration was applied due to the reductions in NOx and increases in soot emissions. Lastly, the results of N2O emissions showed slight decreases in the combustion of oxygenated fuels when using the drop-in calibration, but these emissions returned to similar diesel levels when applying the optimized calibration. Overall, the results of the investigation show the potential of these LCFs to meet the regulations but also not sacrificing the emissions performance of unregulated species.