DieselNet Technology Guide » Engine Emission Control
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The 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.
| Strategy | Description | Fuel Economy Effect |
|---|---|---|
| Engine replacement or upgrade | Accelerated replacement of old technology engines with new engines or with engines rebuilt to a lower emission level. For large stationary, rail and marine engines, upgrading of the engine at engine overhaul to a lower emission level can be a legal requirement. | In most cases, newer technology engines show improved fuel economy |
| Emission control retrofit | Installation of exhaust gas aftertreatment devices on existing engines | Typically, engine optimization is not carried out as part of the retrofit and a fuel economy penalty, usually limited, is possible due to increased exhaust backpressure and/or energy consumed by active retrofit systems |
| Engine operation and maintenance | Reduce unnecessary engine idling, improve driving habits, implement proper maintenance programs | Many operational and maintenance measures can improve fuel economy |
| Alternative fuels | Use alternative fuels and/or fuel additives | Fuel 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 conducted under the Diesel Emissions Reduction Act (DERA) can be found in several reports submitted by the US EPA to Congress [3998][3999][4000][4405][5620]. In Europe, retrofits for in-use diesel engines are driven by urban Low Emission Zone and Low Emission Construction Zone requirements [5073].
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