Optical diagnosis on combustion characteristics and flame development process of Fischer-Tropsch diesel/biodiesel blends

Taking advantage of the complementary physicochemical properties of biodiesel and Fischer-Tropsch (FT) diesel, the use of FT diesel/biodiesel blends can potentially overcome the limitations of biodiesel and improve engine performance. In this study, the combustion and flame development characteristics of FT diesel/biodiesel blends at different loads and injection pressures were investigated on an optical engine. The results show that blending FT diesel with biodiesel reduces ignition delay (ID), improves fuel atomization, and increases indicative thermal efficiency by 2 %–4 % at 50 % FT diesel blending ratio (FT50) compared to pure biodiesel. At low and middle loads, blending FT diesel with biodiesel decreases fuel-bound oxygen concentration, increasing in-cylinder temperature and promoting soot generation. At high load, blending FT diesel with biodiesel promotes fuel atomization and evaporation, which restrains soot generation. Furthermore, increasing injection pressure can reduce local fuel-rich zones, and increase the combustion speed and thermal efficiency while suppressing soot generation. The greater the proportion of FT diesel, the more obvious its improvement in combustion. Specifically, FT50 increases indicative thermal efficiency by 2.3 % at an injection pressure of 140 MPa compared to 80 MPa.