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Control Options for Nox Emissions From Gasoline Fuelled Vehicles
Published May 13, 1997 by Coordinating European Council in Belgium
The contribution that vehicle emissions make to ambient NOx concentrations throughout Europe has recently received much attention. One of the major conclusions of the European Auto/Oil program was that existing vehicle emissions control measures will result in ambient air quality targets being achieved throughout Europe for hydrocarbons, carbon monoxide and benzene by 2010. However, predictions suggest that ambient air quality targets for NOx will still be exceeded in some parts of Europe after 2010 and therefore further regulations are required to bring NOx into attainment before 2010. Thus, during 1996 the European Commission proposed future vehicle exhaust emissions limits for 2000 and 2005 (indicated limits), and fuel specifications for 2000. In 1998, a further proposal may be made for vehicle emissions limits and fuel specifications for 2005.
Numerous investigations have been published reporting the effects of vehicle technology, catalyst formulation and fuel properties on vehicle emissions, including the European Program on Emissions, Fuels and Engine Technology (EPEFE). This paper summarizes and discusses some of the more recent publications.
EPEFE investigated both gasoline and diesel fuel effects, however, this paper only considers possible options for controlling the NOx emissions from gasoline fuelled vehicles. The relative impacts of vehicle technology improvements and fuel reformulation on NOx emissions are compared. Vehicle technology changes of particular interest include: air/fuel ratio strategy, exhaust gas recirculation, catalyst formulation, including platinum group metal (PGM) loading, catalyst volume and catalyst position. The impact of changes in certain fuel parameters such as sulphur and aromatic contents and distillation on NOx emissions is also presented.
Although not assessed here, it should be recognized that non-technical programs such as traffic management, inspecti maintenance and accelerated fleet turnover will have a large impact on vehicle exhaust emissions and thus on ambient air quality, as will stationary sources. It is anticipated that some of these programs may be more cost effective solutions to improving ambient air quality than further reductions in vehicle exhaust emission limits or severe fuel reformulation.