[Effects of Different Precious Metal Loads of CDPF on Characteristics of VOCs Emissions from a Diesel Bus].

ABSTRACT

Based on heavy chassis dynamometers, an experimental study was conducted in a diesel bus with proton transfer reaction mass spectrometry (PTR-MS). It investigated the effects of volatile organic compound (VOC) emission characteristics with three different diesel oxidation catalyst (DOC)+catalyzed diesel particulate filter (CDPF) after-treatments for a typical Chinese city bus driving cycle (CCBC). The results reveal that the major compounds from the diesel bus are OVOCs, aromatic hydrocarbons, alkenes, alkanes, nitrogenous organic compounds, and polycyclic aromatic hydrocarbons (PAH), and that the OVOCs account for more than 50%of the total VOCs. With the same precious metal composition and ratio of the proportion in the CDPF catalyst, the emissions of VOCs decrease with an increase in precious metal load. The emission reduction rates of the VOCs are 36.2%, 40.1%, and 41.4%, respectively, when the precious metal loads are 15 g·ft-3 (type A after-treatment device), 25 g·ft-3 (type B), and 35 g·ft-3 (type C). The average emission rates of alkanes for the three kinds of DOC+CDPF after-treatments are all over 59% for the entire CCBC cycle. The type C after-treatment device can reduce the alkane emissions by 70.2%, with a slight advantage for the OVOC reduction compared with type A and type B devices. For unsaturated hydrocarbons, including aromatic hydrocarbons, alkenes, and PAHs, the after-treatment devices have a catalytic effect, but there is no significant difference between them. The emissions of nitrogenous organic compounds are greatly decreased, by 50.5%, with the type A after-treatment, but the reduction rate decreases with an increase in precious metal load. In addition, OVOCs, aromatic hydrocarbons, and alkenes are the most important contributors to ozone formation. The adoption of DOC+CDPF reduces the emissions of VOCs and, therefore, the ozone formation potential. Taking into account the emission reduction rates and costs of the three different after-treatments and for weighting coefficients of 0.8 and 0.2, respectively, the type B after-treatment is the optimal solution.