Biofuel is a renewable fuel and can be used as a replacement for diesel. Pyrolysis oil can be derived from non-edible de-oiled seed cakes. This investigation focuses on the exergy investigation of a compression ignition (CI) engine to maximize the work exergy (availability) and minimize the destroyed exergy, powered by Aegle marmelos (AM) de-oiled seed cake bio-oil blends. A dual blend of diesel and AM pyrolysis oil was taken in ratios, F0 = 100 + 0, F5 = 95 + 5, F10 = 90 + 10, F15 = 85 + 15, and F20 = 80 + 20 and were tested on a constant speed CI engine at standard compression ratio. The investigational analysis exhibited that a high amount of oxygen content in AM pyrolysis oil blends increased the brake thermal efficiency and decreased the brake-specific fuel consumption compared with diesel (F0). The owing exergy efficiency was obtained from the F20 blend (57.21%) at 100% load (W). Based on the investigation, considering availability and performance behavior of F5, F10, F15, and F20 blends were suggested as suitable biofuel alternatives to diesel.