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Conventional diesel trucks produce significant amounts of pollutant emissions - especially particulate matter (PM) and nitrogen oxides (NOx) - that cause a deterioration of air quality. In order to reduce these emissions, there are a variety of different emission control technologies available.

Substantial emissions benefits can be obtained by repowering older vehicles that are now equipped with old high emitting diesel engines to use the latest low emissions diesel technology. Heavy duty engines are typically overhauled and rebuilt several times over the life of the vehicle, at a cost of $4000 to $8000 or more, depending on the size and the circumstances. Instead of rebuilding the existing engine, in many cases it would be possible to replace it with a new diesel engine meeting current standards, provided that the engine fits into the engine compartment and that it is adapted or adaptable to the drive train.

The United States (US) and the European Union (EU) are introducing successively tighter emission standards for engines used in heavy duty vehicles. The following table lists the standards regarding the most important pollutants, NOx and PM, for the timeframe until 2010 ( w1 ). All the tests are carried out by the use of an engine dynamometer.
It should be noted that since the conditions under which these standards must be achieved (test procedures) differ between the US and the EU, the values given below only provide a general impression of the legal demands, not an exact and direct comparison.

Nitrogen oxides
(NOx)g/kWh (g/bhp-hr)
Particulate matter
(PM)g/kWh (g/bhp-hr)
Year United States European Union United States European Union
1996 (EURO II)
7.0 (5.3)

0.15 (0.11)
1998 (US 1998) 5.3 (4.0)
0.07 (0.05)**
2000 (EURO III)
5.0 (3.8)

0.1 (0.075)
(US 2004)***
3.3 (2.5)*
0.07 (0.05)**
2005 (EURO IV)
3.5 (2.9)

0.02 (0.015)
2007 (US 2007) 0.27 (0.20)
0.013 (0.01)
2008 (EURO V)
2.0 (1.5)

0.02 (0.015)

Including 0.67 (0.5) non-methane hydrocarbons (NMHC) - manufacturers have the flexibility to certify their engines to one of two options, the alternative being a combined limit of 3.2 (2.4) NOx+NMHC
** in-use PM standard 0.09 (0.07)·
*** As part of a consent agreement with the US government, most diesel manufacturers will comply with these standards in October 2002.

B razil and Argentina have introduced EURO II standards as reference standards (with slight modifications) from 1998 onwards (w1 ) and Chile is looking to introduce 50-PPM Sulfur in diesel fuel and Euro 3 standards in 2004. As part of a comprehensive package of measures, Chile has concluded that these measures will cost $127 million per year but have benefits of $260 million per year.


The potential of emission control devices to reduce pollutant emissions depends on a number of factors, including the type of technology used, whether or not low sulfur diesel is used, and whether adequate inspection and maintenance is carried out.

The US EPA provides a very comprehensive overview of emission reduction potentials and other parameters such as prices, sulfur tolerance and fuel penalty for a number of emission control technologies ( w2 ).

A summary of available new engine standards can be found at


Diesel trucks in general can be considered to be very reliable, especially in comparison to newer technologies employing alternative power trains. Diesel engines look back on a comparatively long evolution of continuous development. In reliability tests of alternative fuel trucks, diesel trucks serve as the reference.


Compliance with the Euro I standards generally required modest changes in engine design to minimize particulate emissions, as well as improvements to the fuel injection system. Compliance with the Euro II standards is somewhat more difficult, generally requiring the use of turbochargers and aftercoolers as well as high-pressure fuel injection - generally with computer electronic control of the fuel injection timing. However, the turbocharger and aftercooler should also help to reduce fuel consumption by about 10%. Meeting the U.S. 1998 and/or Euro III standards will require further improvements in fuel injection and electronic engine control systems.

The incremental cost compared to the Euro II standard can be US$1,000 to $1,500. These numbers do not reflect the cost of producing diesel fuel with lower sulfur content, which would be a prerequisite for using Euro III engines with catalytic converters.

Further costs that have to be taken into account include those for inspection and maintenance, fuel economy penalty (or gain) and low sulfur fuel. The actual emerging costs will be a function of the individual applications and situations. The US EPA estimated the additional cost for low sulfur fuel (15 ppm maximum compared to 500 ppm maximum) at 4 - 5 cents per gallon. (For further cost estimates of low sulfur fuels, see Cleaner Fuels.)


Engines meeting Euro and US standards are widely available around the world.

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