Diesel engines are the main power system for heavy-duty and non-road vehicles in Europe. These reliable, fuel-efficient, high torque engines power many of the world's heavy-duty trucks, buses, and non-road vehicles such as construction and agriculture machineries.
While diesel engines have many advantages, they have the disadvantage of emitting significant amounts of toxic particulate matter (PM) and nitrogen oxides (NOx) into the atmosphere. Health experts have concluded that those pollutants adversely affect human health and contribute to acid rain, ground-level ozone and reduced visibility.
Studies have shown that exposure to untreated diesel exhaust causes lung damage and respiratory problems and there is increasing evidence that diesel emissions may cause cancer in humans.
Based on a comparison of vehicles of the early 90's and Euro VI (2013-14) standards, European legislation will have led to emissions reductions for heavy-duty engines of 97% on NOx and PM in less than 25 years. Thus new vehicles become clean but the legacy fleet of old heavily polluting vehicles still largely contributes to urban air pollution issues since fleet penetration appears to be a 15 to 20 year process and limits rapid progress to the targeted air quality benefits.
A research project was conducted in 2006 for the European Commission on how the EU can support the greater use of technical measures such as emissions control systems that can help reduce the emissions of particulates and NOx from existing heavy-duty and captive fleets. Low Emission Zones are progressively implemented in many urban areas in Europe and these request diesel vehicles to meet a satisfactory level of exhaust emissions before they are allowed to drive inside the zone.
Companies that manufacture emission control devices have responded to the challenge of reducing the air pollution from diesel engines already on the market. Through their efforts, cost-effective retrofit technologies have been developed to reduce harmful emissions of existing heavy-duty vehicles and non-road mobile machinery.
Within the various mobile source sectors (e.g., trucks, urban buses, construction, mining and materials handling machines), diesel retrofit technologies have demonstrated their ability to significantly reduce unwanted emissions at reasonable costs without jeopardizing vehicle or machine performance.
Support and Examples of Diesel Retrofit in Europe
Diesel Retrofit Technologies
Emission control technologies include catalytic converters and particulate filters. They consist of a stainless steel box (or can) mounted in the exhaust system either as original equipment or retrofit emissions control device. In some retrofit applications, they can even be mounted in the original muffler.
Inside the can is a catalyst or a particulate filter. The catalyst can be a ceramic or metallic substrate with an active coating incorporating chemical compounds (the washcoat) to support a combination of catalytic metals or minerals selected for their effectiveness in the required emissions reductions. It can also be a homogeneous honeycomb-ceramics in which only active compounds are extruded simultaneously. The catalyst or the particulate filter is mounted in a can and is protected from vibration and shock by a resilient ‘mat’. The emission control device then looks similar to an exhaust muffler. Typical emission control devices available for retrofit applications are Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC), and Selective Catalytic Reduction (SCR) catalysts. They allow the reduction of Particulate Matter (PM) – soot particles – and NOx emissions from existing diesel engines and vehicles.
|Technology||Emission reduction potential|
|Partial Flow Filter||30-60 %||<5%|
|Diesel Oxidation Catalyst||<25%||N/A||<5%|
|Selective Catalytic Reduction||<10%||>70%
(up to 95%)
(up to 95%)
Typical PM and NOx reduction potential for various retrofit devices.
Fuel economy and CO2 emissions should not be negatively impacted by the use of a retrofit emissions control device provided the system is properly designed for the particular applications. Biofuels can affect engine-out emissions and performance; therefore, their impact should be evaluated before fitting a retrofit emissions control system on an existing vehicle.