Abstract
In the last 30 years, diesel engines have made rapid progress to increased efficiency, environmental protection and comfort for both light- and heavy-duty applications. The technical developments include all issues from fuel to combustion process to exhaust gas aftertreatment. This paper provides a comprehensive summary of the available literature regarding technical developments and their impact on the reduction of pollutant emission. This includes emission legislation, fuel quality, diesel engine- and exhaust gas aftertreatment technologies, as well as particulate composition, with a focus on the mass-related particulate emission of on-road vehicle applications. Diesel engine technologies representative of real-world on-road applications will be highlighted.Internal engine modifications now make it possible to minimize particulate and nitrogen oxide emissions with nearly no reduction in power. Among these modifications are cooled exhaust gas recirculation, optimized injections systems, adapted charging systems and optimized combustion processes with high turbulence. With introduction and optimization of exhaust gas aftertreatment systems, such as the diesel oxidation catalyst and the diesel particulate trap, as well as NOx-reduction systems, pollutant emissions have been significantly decreased. Today, sulfur poisoning of diesel oxidation catalysts is no longer considered a problem due to the low-sulfur fuel used in Europe. In the future, there will be an increased use of bio-fuels, which generally have a positive impact on the particulate emissions and do not increase the particle number emissions.Since the introduction of the EU emissions legislation, all emission limits have been reduced by over 90%. Further steps can be expected in the future. Retrospectively, the particulate emissions of modern diesel engines with respect to quality and quantity cannot be compared with those of older engines. Internal engine modifications lead to a clear reduction of the particulate emissions without a negative impact on the particulate-size distribution towards smaller particles. The residual particles can be trapped in a diesel particulate trap independent of their size or the engine operating mode. The usage of a wall-flow diesel particulate filter leads to an extreme reduction of the emitted particulate mass and number, approaching 100%. A reduced particulate mass emission is always connected to a reduced particle number emission.
Highlights
From a technical perspective, diesel engines are caught in an area of conflict between a wide variety of requirements ranging from maximum customer benefit, minimum fuel consumption, to minimum emissions
Based on the results of the particle number emission measurement in the New European Driving Cycle” (NEDC) of new, conditioned vehicles, it appears that there can be wide variations for different vehicles of the same type and model and that, even for repeated measurements performed on the same vehicle, differences in the range of roughly 100% must be taken into account
The comparison of 3 different methods for particulate measurement purposes (2 methods for particle number emission measurement, one method for particulate mass) showed that the differences are for the most part due to the variations in vehicle emissions and not due to inaccuracies in the measurement technology
Summary
Diesel engines are caught in an area of conflict between a wide variety of requirements ranging from maximum customer benefit, minimum fuel consumption, to minimum emissions. While CO2 output has only recently been regulated, statutory emissions limits have been in place since the 1970s. In the beginning of the 1990s, the “Euro” emission standard was introduced, where limits continue to become more stringent in individual emission levels. The currently valid legislation level Euro 5 will be replaced by Euro 6 in 2014. To comply with the legislative limits, or to comply with the future limits prior to the deadlines and to simultaneously meet all customer requirements, systematic further development of diesel engines is necessary. In addition to further developing the engines, exhaust aftertreatment systems were introduced in order to lower engine emissions
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