Future legislations claim further reduction of all restricted
emissions as well as the limitation of soot emissions in diesel
engines. Special alternative diesel fuels that do not contain
aromatic compounds, therefore, promise great potential for further
reduction of HC, CO and particulate emissions.
During a research project carried out at the Institute for
Powertrains and Automotive Technology at the Vienna University of
Technology, the potential of alternative diesel fuels was
investigated using a state-of-the-art diesel engine with common
rail direct injection. The testing took part using an engine test
rig as well as on the chassis dynamometer test bench to demonstrate
the emission levels in real life conditions. As real biofuel, pure
HVO (Hydrogenated Vegetable Oil) was investigated and additionally
in different blends with fossil diesel fuel.
The results on the engine test bench show that HVO can reduce
the NOx-particulate trade-off up to 50% compared to
conventional diesel, whereas this is not the case at all load
points. Especially in low-load conditions, the high cetane number
of the alternative fuel leads to a decreased ignition delay and
thereby reduces the potential to lower particulate emissions.
Besides the reduction of particulate emissions, the fact that
HVO does not contain any aromatic compounds also helps to reduce
unburned HC and CO emissions. For both, a reduction of up to 50%
could be achieved compared to fossil diesel, whereas the magnitude
of the decrease depends on the temperatures occurring during the
combustion. Due to the fact that today's diesel engines often
have low exhaust gas temperatures, the cold start phase is very
important. During the time before the light off of the oxidation
catalyst has taken place, low unburned raw emissions can mean a big
advantage in real life conditions.
Another important issue is the influence of different fuels on
the oil dilution, especially during late injection events as
necessary for the regeneration of particulate filters. In this case
HVO leads to an increasing wall impact and thereby dilution of the
lubricant oil.