Effects of waste-cooking-oil biodiesel blends on diesel vehicle emissions and their reducing characteristics with exhaust after-treatment system

Abstract

The waste-cooking-oil biodiesel is proven to be a clean alternative fuel, its effect on the vehicle emissions at different driving conditions needs further quantitative evaluation, especially with the exhaust after-treatment. The objective of this study is to quantify the effect of waste-cooking-oil biodiesel on the gaseous and particulate emissions from an urban bus at different driving conditions, and with a combination of diesel oxidation catalyst (DOC) and a catalyzed diesel particulate filter (CDPF) after-treatment. Results showed that the emissions depended on the driving conditions, vehicle acceleration and high speed increased the emissions. The biodiesel blends produced a reduction in the carbon monoxide (CO), total hydrocarbon (THC), particle number (PN) and particle mass (PM) emissions, but an increase in the carbon dioxide (CO2) and nitrogen oxide (NOx) emission, and this changing trend increased with not only the biodiesel blending ratio but also the vehicle speed and acceleration. The particle size distribution remained bimodal logarithm distribution after using the biodiesel, and more accumulation mode particles reduced compared with nucleation mode ones, increasing the proportion of nucleation mode particles. The after-treatment system composed of DOC and CDPF could reduce 58.0% of the CO and 53.1% of the THC when using B10 (10% biodiesel and 90% diesel by volume), and the reduction effect was enhanced with the increase of the biodiesel blending ratio, also with the increase of speed and acceleration. The after-treatment system reduced more than 99% of the PN and 94% of the PM, achieving excellent reduction effects, independent of fuel type and driving conditions.