CleanUp Technologies: Exhaust Gas Recirculation

Exhaust gas recirculation has been fitted to all light duty diesels in Western Europe for some years, but will not be used on medium and heavy duty applications until Euro 4 standards are introduced.

EGR, as a retrofit on existing heavy duty engines, has been fitted to 200 buses in Stockholm, Sweden and has been shown to provide around 50% NOx reduction.

The package consists of a valve (under electronic control) that utilises the exhaust back-pressure to allow flow back to the inlet manifold in a normally aspirated engine or to the compressor inlet in a turbocharged engine. The exhaust has been passed through a particulate trap to remove abrasive particles. The system may be further enhanced by a special oil cleaner that maintains the lubrication oil characteristics. With EGR there is a risk of sooting of the lubrication oil. This leads to a rapid thickening effect with potentially high rate of engine wear or failure - the oil cleaner minimises this risk and can give a small fuel consumption benefit due to reduced oil drag (engine friction).

Since a particulate trap is also fitted, the usual emissions reduction benefits of that device are gained; 95% particulates, 90% carbon monoxide and 90% hydrocarbons.

EGR is considered to be a "fit-and-forget" system. Note that the particulate trap will require removal of ash as a service item. TransportEnergy will also offer a maintenance grant of £450.

Grants for EGR on Dennis Dart bus are now available. Other applications are in development.