Comparative Analysis of Combustion Behaviors and Emission Characteristics of Diesel Engines Fueled with Biodiesel or Biodiesel Blends

[Image: see text] In this study, we carried out an experimental analysis of combustion behaviors and emission characteristics of pure biodiesel and biodiesel–dimethyl ether (DME) blends and determined the impacts of the biodiesel ratio and the nozzle parameter on the combustion pressure characteristics in the time domain/frequency domain and emission characteristics. The findings show that with a decrease in the biodiesel proportion in biodiesel–DME blends, the maximum combustion pressure and fuels in the premixed combustion stage decrease with a retarded maximum value phase, but the maximum heat release in diffusive combustion increases and the maximum amplitude of pressure rise acceleration decreases. All of the pressure level curves of BD100, BD80, and BD50 contain a rapid decrease stage 1, a slow decrease stage 2, and a fluctuating stage 3. With a decrease in the biodiesel proportion, the exhaust gas temperature, NO(x) emissions, and smoke emissions of BD100, BD80, and BD50 decrease gradually. Compared with a 5 × 0.43 mm nozzle, the maximum combustion pressure and maximum heat release rate of BD50 for a 4 × 0.35 mm nozzle were higher and the phase of the maximum value was advanced. Soot emissions for the 4 × 0.35 mm nozzle were lower, which is especially obvious under a high brake mean effective pressure (BMEP).