Energy efficient reduction of exhaust emissions from vehicles: E4 Mistra

Research Project, 2006 – 2009

It is becoming more and more evident that the problem of global warming is the largest environmental challenge we face at present. The emission of anthropogenic CO2 is the largest factor contributing to global warming. Since a large fraction of the CO2 emissions originates from the transport sector measures have to be taken here. This can be in the form of sustainable (bio-) fuels, fuel cells using hydrogen produced from water and solar-cells. An important short-term contribution is to develop and stimulate the use of more fuel-efficient engines. Although new propulsion systems are emerging, such as hybrid power-trains and fuel cell systems, analysis shows that combustion systems with excess oxygen, such as the diesel engine, will be the most important engine concept for the next 20 years. However, while improving the fuel consumption it is important to also reduce the emissions of harmful substances like nitrogen oxides (NOx) and particulate matter (PM). These emissions can be reduced by different after-treatment systems, most of which involve a small fuel penalty. The goal of this project is to demonstrate very low emission levels (0.005 g PM/kWh and 0.1 g NOx/kWh) with an engine exhibiting low CO2 emissions. These levels can be compared with the most stringent legislative levels decided (0.013 g PM/kWh and 0.27 g NOx/kWh). The very low emission levels combined with the high fuel efficiency can be achieved by using advanced components such as innovative catalysts and substrates, reformer technologies and heat recuperation. As mentioned, a disadvantage with the present methods for PM and NOx removal is the increased CO2 production caused by the increased fuel consumption that is related to the after-treatment system. European manufacturers of light-duty vehicles have promised to reduce the CO2 emissions by 25% from 1995 to 2008, largely by using diesel engines instead of gasoline engines. The fuel consumption is in general more important for buyers of heavy-duty commercial vehicles, but also here legislative means are expected.

The project aims at developing a competence in energy-efficient new after-treatment systems for combustion engines. The methods are independent of the fuel (i.e. bio-diesel, DME, fossil diesel), but are directed towards engines with excess oxygen, since these systems appear to produce the lowest CO2 emissions also when used with renewable fuels. Although highly efficient, diesel engines produce a lot of waste heat, which can be utilized according to the methods described in this proposal. This will lead to further decrease in CO2 emissions. The project uses four recent technology advances: Thermoelectric materials for heat recuperation, catalytic reduction of NOx using hydrocarbons from the fuel, fuel reformers with high efficiency and innovative catalyst substrates for minimized heat losses in the after-treatment system.