A systematic study into the effect of lignocellulose-derived biofuels on the combustion and emissions of fossil diesel blends in a compression ignition engine

Screening of a variety of bioderived furanic molecules was performed in order to improve our understanding of how this class of molecules respond during compression-ignition combustion, after blending with diesel fuel. Reducing carbon emissions is possible through the use of “2nd generation” carbon neutral biofuels, the sources of which are from non-edible feedstocks, meaning that competition with food resources is negated. The tested molecules were selected for their potentially more economic and less energy intensive production routes, compared to more conventional alternative diesel fuels. These furan-based molecules were varied in their degree of molecular saturation, their branching and in the addition of an oxygenated functional group. It was found that the molecules liberated from lignocellulosic biomass need to be saturated to achieve stable combustion when blended at a volumetric ratio of 50:50 with fossil diesel. The aromatic ring of a furan molecule was postulated to be difficult to break down and increased the ignition delay substantially. This resulted in a significant increase in carbon monoxide (CO) emissions. Blending with butanol and increasing the proportion of diesel in the blend mitigated this effect, and enabled the effect on emissions of adding furan molecules into a blend to be evaluated with a wider range of candidate molecules. Biofuel combustion produced higher NOx emissions and particle number, while particle mass decreased compared to the fossil diesel. Between the molecules, an increase in the degree of saturation decreased the ignition delay, which tended to decrease the NOx emissions and increase the particle mass. Furthermore, the effect of adding alkyl chains to the ring structure tended to increase the molecules’ propensity to ignite by providing more radicals during the ignition delay period; longer single chains were more effective compared to numerous shorter chains. It was also noted that the addition of an oxygenated functional group to the molecule decreased the particle mass in all cases. Carbonyl groups decreased the ignition delay period relative to the base molecule while alcohol groups increased this period; in both cases, however, NOx emissions increased