The effect of diesel and biodiesel blends on particle size and number concentration distributions were studied in diesel engine under different operating conditions, including speeds, loads, and injection timing. The results showed that the engine load was more influential on particle size distribution than the engine speed. At the high load, diesel fuels produced mainly accumulation-mode particles, and at medium or lower load, diesel fuel produced more nuclei-mode particles. The injection timing had obviously influence on particle size distribution and number concentration. Advanced injection timing induced higher number concentrations of nuclei-mode particles for the low load and more accumulation mode particles for high load. Compared to the neat diesel fuel, the combustion process was improved when fueled with diesel-biodiesel blends. The oxygen contained in the biodiesel fuel may improve combustion. The number and mass concentration of PM was greatly decreased with the increase in biodiesel blend ratio. Biodiesel blends had an early start of injection, and particle size distributions tended to be ultra-fine particles with the increase in the ratio of biodiesel blend. The average mid-diameter range of particles was significantly affected by the change in fuel injection timing.
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