Effect of Fuels on Compression Ignition Engine Particle Size Distribution and DPF Filtration Efficiency

A diesel engine was run on off-highway cycle sequence on nine (9) fuels and blends. Number-weighted solid particle size distribution (PSD) in the size range from 5.6 nm to 560 nm was measured at inlet and outlet of a diesel particulate filter (DPF) on a sequence of five (5) non-road transient cycles (NRTCs) and five (5) non-road steady-state cycles (NRSCs). The measurements were used to correlate the fuel properties to the DPF-In concentrations and filtration of different size particles in the DPFs. The data showed an expected trend with the DPF-In emissions. Ultra-low sulfur diesel (ULSD) had the highest solid particle number (SPN) concentrations and biodiesels (soy-based biodiesel (B100) and rapeseed-based biodiesel (RME)) had the lowest concentrations. The geometric number mean diameter (GNMD) of DPF-In PSD correlates with the concentrations. The calculated GNMD was the highest for ULSD and lowest for B100/RME. An opposite trend for the GNMD was observed at the DPF-Out where the GNMD for B100/RME was higher than that for ULSD. For a specific fuel, the filtration efficiency for 34 – 50 nm particles was higher than that for 50 – 165 nm particles, reflecting a higher filtration efficiency for smaller particles by diffusion, and resulting in higher GNMD for DPF-Out relative to DPF-In. As more soot is loaded on the surface of the DPF, the filtration efficiency of the larger particles improves due to soot caking, which will shift the GNMD back to a smaller size. This dynamic process of the size distribution between DPF-In and DPF-Out shed some light on how a specific DPF interact with a specific fuel, and how one can improve the design of the DPF to attain high efficiency across the different particle size range, regardless of the fuel used. This work suggests that the design of the DPF will have to take into consideration the use of different fuels in order to avoid biasing the size distribution and number emissions higher than the case when using ULSD.