REBECa WP IV - Formation and transformation of particles and other pollutants from engines using biofuel: WP IV final report (DTU project no. 50502)

This project expands present knowledge regarding diesel engine emissions and diesel particulate filter (DPF) performance and regeneration during biodiesel usage. This is done through a literature survey, a pilot-scale experimental study of DPF performance and thermo gravimetric studies of PM/catalyst/ash interactions. A pilot-scale experimental study of DPF performance and NO2 influence indicated a lower engine out particulate concentration while using Rapeseed methyl ester (RME, 26 mg/m3) compared to ultra low sulphur diesel (ULSD, 58 mg/m3). Filter regeneration with a 50 % diluted exhaust also showed an improved performance with RME (regeneration at 475 oC and 120 mbar filter pressure loss) compared to ULSD (500 oC and 125 mbar filter pressure loss). The improved filter performance was most likely due to the lower particulate concentration when using RME (lower deposition flux to overcome), because no significant differences in particulate reactivity or engine out NOx concentration were seen. The introduction of 400 ppm NO2 to the RME exhaust (normal NOx concentration ~ 250 ppm (can be oxidized to NO2 by an oxidation catalyst)) caused an improved filter regeneration performance (regeneration at 435 oC and 80 mbar filter pressure loss), which illustrates the importance of NO2 for particle oxidation and thereby the importance NO to NO2 conversion either in a separate oxidation catalyst or as part of the DPF’s catalytic performance. Thermo gravimetric (TG) studies of PM/catalyst/ash interactions in N2 with 10 % O2 showed that diesel PM conversion (5:1 wt. ratio with commercial catalyst) benefits from the presence of biodiesel salts such as Na2CO3, K2CO3 or K3PO4 – TG peak conversion temperature decreased from 526 ± 19oC to ~ 400-420 oC, with a limited dependence on salt concentration. Other lube oil derived salts (CaSO4 and Ca(H2PO4) or combinations of lube oil and fuel (K2SO4) can have a detrimental effect on catalytic PM conversion. However, utilization of high biodiesel fractions over a prolonged period of time will likely be necessary before any of these effects can be seen, because of the stringent fuel specifications (EN 14214: ≤ 5 mg Na + K/kg; ≤ 5 mg Ca + Mg/kg; ≤ 4 mg P/kg).