The potential of two alternative Diesel fuels, NExBTL from NesteOil® and Fischer-Tropsch- Diesel from “Biomassekraftwerk Güssing”, was investigated during the engine operation, concerning the reduction of exhaust emissions in the course of a 14 month lasting project.
As result of the fact that those fuels are literally free of aromatic compounds, both fuels offer great potential to reduce HC, CO and particulate emissions. The results on the engine test rig demonstrated, that the advantage to lower particulate emissions can be transferred to favour of NOx emissions by adjusting parameters in the engine calibration.
As result of constant NOx emissions all fuels show the same level of NO2 emissions. The level of polycyclic aromatic hydrocarbons is on such a low level for fossil diesel fuel that it is below the detection limit of the FTIR measurement device as well as for the chemical offline analysis carried out afterwards. Aldehyde emissions can only be traced by chemical analysis, whereas a further reduction of those emissions can be obtained by the admixture of NExBTL.
Besides the study on the engine test rig all fuels where investigated on the roller dynamometer as well during the New European Driving Cycle (NEDC), where a significant reduction of HC and CO emissions can be achieved. On the roller test bench this reduction is even higher than compared to the results from the engine test bench. There were no significant differences in the efficiency behaviour for all fuels, which leads to a reduction of CO2 emissions by 5% for pure NExBTL during the NEDC as result of a lower C/H ratio.
For the regeneration of the particulate filter (DPF) high amounts of post injected fuel are necessary to produce the high temperatures upstream the DPF. For this matter the amount of post injected fuel has to be raised with pure NExBTL compared to fossil diesel, because an increasing amount of fuel is being converted inside the engine as result of the high cetane number. This means that this fuel cannot be provided to the catalyst to increase the temperature. As result, the amount of fuel being inserted into the lube oil is increasing with NExBTL compared to fossil diesel during this injection strategy. After the engine produces less soot when NExBTL is used, the number of regenerations of the particulate filter is being reduced. This means that the effect of oil dilution hast to be evaluated regarding the whole vehicle.
To sum up, both fuels are well suited for the use in an internal combustion engine and result in a reduction of HC, CO and particulate emissions. Although, when high admixing rates are used, there is an increasing risk of oil dilution during the particulate filter regeneration.