Diesel engines are amongst the largest emission sources in
urban air. The emissions consist of soot particles of about 40-80 nm in
diameter. The engines emit also nanoparticles at less than 20 nm or so in
diameter, consisting of various hydrocarbons and possibly also sulphur (in case
of sulphur containing fuel).
Why it is so attractive to switch to diesel instead of a
less emitting gasoline engine? The answer is in fuel economy, which is one of
the main advantages of using diesel engines. In Finland, the national policy
towards diesel fleet has changed over the last couple of years. Today the price
per liter is almost equal for both diesel and E10 gasoline. The owner of the
diesel car needs to pay monthly tax, and the saving must come from the more
economic engine.
The emissions of diesel engines are rather well know and
there is continuous process to limit the emissions to even lower level. In
2013, the new EURO VI limits for heavy duty vehicles will be for PM
(particulate matter) 0.01 g/kWh and for NOx 0.4 g/kWh. If you compare these to
the EURO I values just 20 years ago the change is dramatic: EURO I for PM was
0.36 g/kWh and for NOx 8 g/kWh. Unfortunately, the diesel engines tend to be
strong and last forever, so we have to wait for a while until the fleet has
majority of EURO VI level engines.
In order to cut down the emissions to EURO VI level, the
changes in engine technology will not be sufficient alone. This points out to
the importance of the after treatment of the exhaust gases. Several different
types of catalysts and filters exist. How well do these work? What is the
efficiency of each one of them? These are the questions to be answered though
intensive research work.
In order to make the development towards lower emissions
even more challenging, one needs to consider also the effects of new type of
fuels. As diesel fuel is possible to be made of e.g. biomass based renewable energy
sources, there are activities to develop these alternative fuel types. These new
generation of fuels aim for lower CO2 footprint.
Recent PhD work has focused on all of these in performing a
wide set of experiments. I will examine the work on Friday 23rd
November. The overall message is clear, one can fight against particle and gaseous
emissions successfully together with lower greenhouse gas emissions.
The link for the press release of the thesis work can be
found here in Finnish:
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