Emission Control from In-Use Engines

W. Addy Majewski, Hannu Jääskeläinen

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Abstract: IC engines in some applications can last for as long as 20-30 years. Technologies are often required to reduce emissions from existing in-use engines. Such technologies include engine replacement, emission control retrofits, engine operation and maintenance, and alternative fuels.


Introduction of new, low-emitting engine models is the most effective strategy to reduce engine and vehicle emissions. However, the air quality improvement is not immediate. A long period of time may be necessary before old engine models are replaced with new ones. This is particularly true for some diesel engine applications where the engines can last for as long as 20-30 years. Technologies are often required to reduce emissions in existing in-use engines, especially in vehicle fleets operated in environmentally sensitive areas, such as in large urban centers.

Strategies to reduce emissions from in-use engines are generally based on technology solutions developed for new engines and vehicles. The most important approaches are listed in Table 1.

Table 1
Emission reduction strategies for in-use engines and vehicles
StrategyDescriptionFuel Economy Effect
Engine replacementAccelerated replacement of old technology engines with new engines or with engines rebuilt to a lower emission levelIn most cases, newer technology engines show improved fuel economy
Emission control retrofitInstallation of exhaust gas aftertreatment devices in existing enginesA fuel economy penalty, usually limited, is possible due to increased exhaust backpressure and/or energy consumed by active retrofit systems
Engine operation and maintenanceReduce unnecessary engine idling, improve driving habits, implement proper maintenance programsMany operational and maintenance measures can improve fuel economy
Alternative fuelsUse alternative fuels and/or fuel additivesFuel and fuel additive specific

The choice of strategy depends on a number of factors, including the technical feasibility—not all strategies are applicable to all engines. An important factor is the cost of emission reduction, typically expressed in dollars per ton of removed NOx or PM.

Wide-scale programs to reduce emissions from in-use diesel engines have been conducted in the United States, both in California and at the federal level. A detailed description of the federal program can be found in three reports submitted by the US EPA to Congress [3998][3999][4000].