Investigations of NO_2 in Legal Test Procedure for Diesel Passenger Cars

摘要

As a result of increased use of catalytic exhaust aftertreatment systems of vehicles and the low-sulfur Diesel fuels there is an increasing share of nitrogen dioxide NO_2 in the ambient air of several cities. This is in spite of lowering the summary nitric oxides NO_x emissions from vehicles. NO_2 is much more toxic than nitrogen monoxide NO and it will be specially considered in the next legal testing procedures. There are doubts about the accuracy of analyzing the reactive substances from diluted gas and this project has the objective to show how NO_2 is changing as it travels down through the exhaust- and the CVS systems. For legal measurements of NO_2 a WLTP-DTP subgroup (Worldwide Light Duty Test Procedures - Diesel Test Procedures) proposed different combinations of NO_x-analyzers and analysis of NO and NO_x. Some of these set-ups were tested in this work. The investigated WLTP – NO_2-measuring methods have been found in the present work as useful tools to estimate the NO_2-levels and there were no indications of reactivity at these low concentration levels. Generally there are no clear tendencies of increasing, or decreasing concentrations of the investigated NO_2 along the gas way. This is the result of different factors, like: reactivity (theoretically influenced by the conditions of flow, temperature and concentrations of reactants), estimate of dilution factor and also emission fluctuations of the vehicle during the test time. The paper also shows some difficulties which arise by estimate of low emission concentrations influenced by several systems and conditions.