Upgrading Pyrolysis Bio-Oil through Esterification Process and Assessing the Performance and Emissions of Diesel–Biodiesel–Esterified Pyrolysis Bio-Oil Blends in Direct Injection Diesel Engines

[Image: see text] This research aimed to evaluate the performance and emissions of direct injection diesel engines using blends of diesel–biodiesel–esterified pyrolysis bio-oil (D–B–EPB). The pyrolysis process was employed to produce pyrolysis bio-oil (PBO) from solid biomass obtained from fresh palm fruits. Furthermore, a simple and effective esterification process was used to upgrade the PBO. The methyl ester (ME) purity of EPB production was studied to optimize three independent variables: methanol (14.8–65.2 wt %), sulfuric acid (1.6–18.4 wt %), and reaction time (16–84 min) using the response surface methodology. The actual experiment yielded a ME purity of 72.73 wt % under the recommended conditions of 40.3 wt % methanol, 13.0 wt % sulfuric acid, 50 min reaction time, 60 °C reaction temperature, and 300 rpm stirrer speed. Additionally, the stability and phase behaviors of D–B–EPB blends were analyzed by using a ternary phase diagram to determine the potential blending proportion. The results revealed that a fuel blend consisting of 30 wt % diesel, 60 wt % biodiesel, and 10 wt % EPB (D30B60EPB10) met the density and viscosity requirements of diesel standards. This D30B60EPB10 blend was subjected to performance and emission tests in diesel engines at various speeds ranging from 1100 to 2300 rpm and different engine loads of 25, 50, and 75%. In terms of performance analysis, the brake thermal efficiencies of biodiesel and D30B60EPB10 were 7.19 and 3.88% higher than that of diesel, respectively. However, the brake-specific fuel consumption of the D30B60EPB10 blend was 6.60% higher than that of diesel due to its higher density and viscosity and lower heating value compared with that of diesel. In the emission analysis, the D30B60EPB10 blend exhibited performance comparable to diesel while being more environmentally friendly, reducing carbon monoxide, carbon dioxide, nitrogen oxide, and smoke opacity by 8.73, 30.13, 37.55, and 59.75%, respectively. The results of this study suggest that the D–B–EPB blend has the potential to serve as a viable biofuel option, reducing the proportion of diesel in blended fuel and benefiting farmers and rural communities..