Emissions Characterization and Particle Size Distribution from a DPF-Equipped Diesel Truck Fueled with Biodiesel Blends.

摘要

Biodiesel may be derived from either plant or animal sources, and is usually employed as a compression ignition fuel in a blend with petroleum diesel (PD). Emissions differences between vehicles operated on biodiesel blends and PD have been published previously, but data do not cover the latest engine technologies. Prior studies have shown that biodiesel offers advantages in reducing particulate matter, with either no advantage or a slight disadvantage for oxides of nitrogen emissions. Literature also suggests that diesel engine exhaust particle number emissions are dominated by nucleation mode particles (NMPs) if present, while the mass emissions are dominated by accumulation mode particles (AMPs). This thesis describes a recent study on the emissions impact and exhaust particles size distribution and composition, under steady state condition, of a 2007 medium heavy duty diesel truck (MHDDT) fueled with two biodiesel blends, B20A and B20B, and PD. The truck was tested in a chassis dynamometer laboratory using three steady state driving cycles. The cycles include vehicle run at 20 mph for 30 minutes (MD1), 32 mph for 30 minutes (MD2) and 50 mph for 20 minutes (MD3). Emissions were measured using a full exhaust dilution tunnel equipped with a subsonic venturi and secondary dilution for PM sampling. A fast particle spectrometer (DMS 500) was used to measure the particle number concentration and size distribution from the vehicle exhaust.;The study showed that emissions were more speed dependent than fuel type. For any given cycle, the differences in CO2 and NOx tailpipe emissions produced by the PD, B20A and B20B were statistically insignificant with variations of between 0.5-1.4%, and 0.5-3.4%, respectively at 95% confidence level. The results further showed that, for MD2, CO2 emissions produced were lowest with corresponding highest fuel economy (miles per gallon (mpg) of fuel consumed). The NOx emissions produced for B20A and B20B were slightly higher than those of PD, except for MD2. Generally, low particulate matter (PM) emissions were produced from the test results due to the truck diesel particulate filter (DPF). The carbon monoxide (CO) and hydrocarbon (HC) emissions were also low, with HC being difficult to quantify as a result of oxidation in the DPF.;Analysis of the exhaust particle data showed that, for all of the driving modes, the exhaust particles existed in two distinct modes with the particle number concentration dominated by the NMPs for all three test fuels. The particle mass concentration, dominated by the AMPs, substantially correlated with the pattern observed in the gravimetric PM mass emissions measurement. It was observed that factors such as DPF loading, dilution conditions (temperature, humidity) that are not fuel related strongly affected particle size formation especially in the NMP range. It was also observed that the total exhaust particle number concentration and the geometric mean diameter (GMD) increased with propulsion power. However, the GMD values were typically in the range of 25-40 nm for all driving modes and fuel type combinations. This is further confirmation that exhaust particles were dominated by nanoparticles that have been reported to cause respiratory diseases and other health effects in humans.