Catalytic Reduction of NOx on Heavy-Duty Trucks

Sammanfattning: The objective of the work described in this thesis is to identify the principles and parts of an aftertreatment system for the catalytic NOx reduction for heavy-duty diesel vehicles, and to demonstrate such a system in full-scale. The reducing agent is diesel fuel. Many advantageous features of the diesel engine, such as life span, reliability and efficiency, make the engine the most frequent power source in heavy-duty vehicles. The most significant disadvantage of diesel engines is their emission of nitrogen oxides (NOx) which have adverse effects on the environment. Consequently, legislative pressure is put on manufacturers of heavy-duty vehicles to decrease truck NOx emissions. A background to NOx emissions and their source and effects is supplied, as is a survey of NOx aftertreatment techniques. Several aspects on heavy-duty diesel deNOx via the use of HC-SCR are accounted for. These aspects consist of, for example, exhaust system design including injector construction and catalyst configuration, reaction models and dosing strategies. In addition, a comprehensive background of the subject is given and the significance of test methods is pointed out. The potential of HC-SCR is indicated, as are its limitations. The relative cost/effectiveness performance of the system suggests that commercial use will be extremely limited. Several system solutions reported in this thesis can, however, be transferred to other similar systems, as the complexity of the problems within the field of NOx reduction show many features in common. A bench-scale study of NOx storage and reduction shows the influence that the choice of experimental procedures has on results and conclusions related to the experimental work. The study indicates that system optimisation is largely depending on the inclusion or exclusion of N2O selectivity in the term "NOx conversion".