Combined effects of soybean biodiesel fuel addition and EGR application on the combustion and exhaust emissions in a diesel engine

•The combining effects of 20% soybean biodiesel and EGR rate were investigated.•EGR application did not cause significant penalties on the engine performance.•NOx and smoke emissions were simultaneously improved. In this study, soybean biodiesel fuel was blended in 20 vol.% with diesel fuel and tested in a single-cylinder, DI, four-stroke diesel engine under four different engine loads (15, 11.25, 7.5 and 3.75 Nm) and 2200 rpm engine speed with different EGR rates (5, 10, 15%). The results showed that the maximum heat release rate and maximum in-cylinder pressure were mostly increased with the combined effects of biodiesel fuel addition and EGR application. Premixed combustion fractions were generally increased at all the engine loads with corresponding decrease in the diffusion combustion fractions. Combustion durations were generally stable while the center of the heat release rates shifted toward TDC. Reasonable increments on the BSFC and reductions on BTE as a maximum 6% and 3% occurred with 15% EGR, respectively. NOx and smoke emissions were improved simultaneously up to 55% and 15% at the high engine load, respectively. THC emissions at the low and medium engine loads decreased while deteriorations were observed with more than 5% EGR at the high engine load. Although CO emissions showed insignificant changes, there were increments at the high engine load. However, CO2 emissions were slightly higher for all the engine loads.