Future fuel formulations including classic refining schemes (hydrotreatment) and synthetic blending stocks like Fischer-Tropsch, oligomerate and high cetane linear ethers were tested for their impact on diesel emissions in various engine conditions (transient and cold operations).
CO, HC, Aldehyde, Particulate and PAH emissions are highly sensitive to fuel quality whereas NOx emissions are only slightly modified.
Very low level of pollutants is obtained with the Fischer-Tropsch fuel. Oligomerisation fuel induces an increase in CO, HC, aldehyde emissions due to its very low cetane number but presents low emissions of particulates and smoke because of its paraffinic composition. Pentyl ether behaves essentially as a high cetane paraffinic hydrocarbon. The relationships between fuel parameters and emissions were also assessed:
CO, HC and aldehyde emissions depend on the cetane number.
Particulates, IOF, smoke and PAHs are controlled by aromatic content and density.
Density also controlled NOx emissions but with far less variation.
Fuel quality can also help to reach a better NOx/particulates trade-off with EGR. Tall-oil methyl ester containing fuel offers a good potential for low emissions because of the beneficial effect of oxygen on particulates.