© 2022 The Institution of Chemical EngineersThis study aims to deeply investigate the effects of the boron nanoparticles reinforced diesel fuel along with various biogas (BG) flow rates (0.5, 1, and 2 L/min) on the engine performance and emission characteristics of a diesel engine. The tests were carried out using a single-cylinder, four-stroke, direct injection, compression-ignition engine at a constant engine speed of 1500 rpm and under the varying engine loads from 2.5 to 10 Nm with gaps of 2.5 Nm. In the results, it is seen that EGT started to decrease in both the addition of boron nanoparticles and the addition of biogas compared to that of conventional diesel fuel (DF). EGT reduced by 8.6% for DF+Boron test fuel, 14.4% for DF+Boron+ 0.5 BG, 21% for DF+Boron+ 1 BG, and 23.4% for DF+Boron+ 2 BG. Compared to diesel fuel, CO, NOx, and HC emissions decreased with the addition of nanoparticles at all loads. However, as the amount of biogas increased, CO and HC emissions increased, but NOx emissions decreased. CO emission dropped by 22.2% for DF+Boron test fuel, however, increased to be 5.6%, 16.7%, and 36.1% for DF+Boron+ 0.5 BG, DF+Boron+ 1 BG, and DF+Boron+ 2 BG respectively. NOx emission reduced by 4.9%, 8.6%, 10.7%, and 14.8% for DF+Boron, DF+Boron+ 0.5 BG, DF+Boron+ 1 BG, and DF+Boron+ 2 BG respectively. In comparison to that of conventional DF, the brake specific fuel consumption (BSFC) value decreased by 8.42% for DF+Boron test fuel due to high energy content of nanoparticles, but it increased by 10.94% for DF+Boron+ 0.5 BG, 28.01% for DF+Boron+ 1 BG, and 60.2% for DF+Boron+ 2 BG. In addition, brake thermal efficiency BTE value increased by 8.04% for boron-added test fuel, but it declined by 9.41% for DF+Boron+ 0.5 BG, 19.38% for DF+Boron+ 1 BG, and 32.2% for DF+Boron+ 2 BG as compared to that of DF. In the conclusion, it is noticed that the engine characteristics have worsened by the introduction of biogas into the cylinder, but these worsened characteristics can be improved with the presence of boron nitride nanoparticles.