Diesel Emission Control Systems: Legislation

Since the first exhaust emission legislation for petrol engines came into force in the mid-1960s in California, the permissible limits for a range of pollutants have been further and further reduced. In the meantime, all industrial nations have introduced exhaust emission legislation that defines the emission limits for petrol and diesel engines as well as the test methods.

Essentially, the following exhaust emission legislation applies:

• CARB legislation (California Air Resources Board), California
• EPA legislation (Environmental Protection Agency), USA
• EU legislation (European Union) and corresponding ECE regulations (UN Economic Commission for Europe), Europe
• Japan legislation.

This legislation has lead to the development of different requirements with regard to the limitation of various components in the exhaust gas. Essentially, the following exhaust gas constituents are evaluated:

• Carbon monoxide (CO)
• Nitrogen oxides (NO_x )
• Hydrocarbons (HC)
• Particulates (PM)

It can generally be said that traditionally more emphasis is placed on low nitrogen oxide emissions in US legislation while in Europe the focus tends to be more on carbon monoxide. The following graphic compares the standard applicable to BMW diesel vehicles with the current standards in Europe. A direct comparison, however, is not possible as different measuring cycles are used and different values are measured for hydrocarbons.

Although European and US standards cannot be compared 1:1 it is clear that requirements relating to nitrogen oxide emissions are considerably more demanding in the US market. Diesel engines generally have higher nitrogen oxide emission levels than patrol engines as diesel engines are normally operated with excess air. For this reason, the challenge of achieving approval in all 50 states of the USA had to be met with a series of new technological developments.

Comparison of Exhaust Emission Legislation 

Fig 1: Exhaust Emission Legislation Comparison Graph

Courtesy of BMW OF NORTH AMERICA, INC.