Diesel engine development is faced with the challenge of reducing the concentration of nitrogen oxides and particulates, while at the same time maintaining fuel consumption at a constant level. Ideally even reducing it. This conflict of aims makes the development task increasingly complex.
Meeting the Euro standards
The Euro 3 limits currently apply, but as of 2005 commercial vehicles will have to conform to the more stringent Euro 4 standard. And by the time Euro 5 comes into force in 2008, noxious harmful emissions will have to be reduced by between 80 % (hydrocarbons) and 90 % (particulates) over the 1990 baseline.
This requires some form of exhaust after-treatment. To this end, engines are designed either for low nitrogen oxide emission or low particulate emission. In each case the other critical exhaust component is subsequently either removed or reduced. Here are the most reliable methods for after-treatment today:
Exhaust Gas Recirculation
Using this method, known as EGR (Exhaust Gas Recirculation), a portion of the exhaust gas can be cooled and routed back to the induced air. This also smoothens the combustion temperature peaks.