Technical evaluation of low-carbon fuels as a decarbonization pathway of the light-duty transport sector

Abstract

The need to rapidly reduce greenhouse gas emissions from the transportation sector has renewed interest in low-carbon fuels, both from the production and utilization standpoint. The maturing of alternative processes to synthesize fuels from atmospheric CO2 and renewable non-edible feedstocks constitutes an interesting proposition, which needs to be matched by favorable drop-in properties and environmental performance once applied to internal combustion engines. To this end, the authors investigate the use of diesel-like high-reactivity and low-reactivity LCFs in a light-duty compression-ignition engine by experimentally assessing their implementation with existing hardware (drop-in) and discussing possible modifications to achieve improved results through calibration. The results revealed that high-reactivity fuels could operate under similar conditions to the standard diesel fuel, exhibiting similar efficiency and soot emissions combined with important reductions in NOx emissions. On the other hand, low-reactivity LCFs show advantages in promoting alternative combustion concepts because of the longer ignition delays, which make it possible to use lower injection pressures and have more stratified air–fuel mixtures, but at the same time, the results revealed that the implementation of these fuels might suffer from hardware limitations which worsens the combustion stability and the operation at low-load. Although the fuels tested exhibited variations in Tank-to-Wheel due to their carbon content and fuel economy, it was found that Well-to-Wheel CO2 intensity is eventually dominated by the renewable content of the fuel and the CO2 is greatly impacted by its production pathway, rather than the fuel consumption optimization. Finally, the study confirmed that, for the successful adoption of oxygenated low-carbon fuels (including alcohols), appropriate material selection in the engine fuel system and fuel additives are necessary to prevent components and seal performance degradation.