Physicochemical Characterization, Engine Performance, and Emission Evaluation of Ternary Fuel Blends: Valorizing Agricultural Plastic Pyrolysis Oil and End-of-Life Transformers

This study presents a systematic investigation of waste agricultural plastic pyrolysis oil (waste plastic oil (WPO)) and waste transformer oil (WTO) as a combined alternative fuel blend for a compression-ignition engine. Agricultural plastic/rubber waste was converted into fuel-grade pyrolysis oil through a novel energy-integrated batch pyrolysis process (1 ton capacity horizontal rotary reactor, 350–450 °C) with a 45% liquid fuel yield. Four fuel blends were prepared and comprehensively characterized: base diesel (D100), a 40% WTO blend (WTO40), a 40% WPO blend (WPO40), and a new ternary blend of 20% WPO +20% WTO (WPO20WTO20). Advanced characterization techniques such as Fourier transform infrared spectroscopy (FT-IR) and distillation curve analysis revealed that all blends met ASTM D6751 specifications for density (830–850 kg/m3) and kinematic viscosity (2.84–4.50 mm2/s) and exhibited outstanding cold flow properties (cloud points −6 to −25 °C, pour points −27 to ≤ −40 °C). Engine performance tests were conducted at four engine speeds (1200, 1600, 2000, and 2400 rpm) on a single-cylinder air-cooled diesel engine under full load. With a 12.59% torque increase, a 14.07% brake power (BP) improvement, and a 3.2% brake specific fuel consumption (BSFC) reduction, WPO20WTO20 was the best-performing fuel. Improvements achieved with WTO40 and WPO40 blends were 11.31% and 9.06% increase in torque and 6.2% and 5.6% decrease in BSFC, respectively. WTO40 provided the highest efficiency improvements, and brake thermal efficiency improvements ranged from 3.8% to 6.7% across all fuel blends. Emission analyses revealed that WPO40 reduced carbon monoxide (CO) emission by an average of 37.35%, while WPO20WTO20 caused an increase by 23.81%. Emissions of nitrogen oxides (NOx) increased significantly in all blends compared to D100: +51.61% in WTO40, +46.73% in WPO20WTO20, and +45.40% in WPO40, consistent with the elevated aromatic content confirmed by FT-IR analysis. Nevertheless, exhaust gas recirculation and selective catalytic reduction aftertreatment systems have demonstrated potential for addressing such NOx increases in published studies; however, their compatibility and performance with WPO–WTO blend exhaust constituents were not experimentally verified in the present study. To the best of the authors’ knowledge, this is the first study to systematically characterize ternary WPO–WTO–diesel blends and document double-digit simultaneous improvements in torque (+12.59%) and BP (+14.07%) along with synergistic distillation behavior (32.1% yield in the 250–300 °C range) and arctic-grade cold flow properties. It should be noted that in-cylinder combustion parameters (heat release rate, ignition delay) and CO2/HC emissions were not measured in the present study due to instrumentation constraints; interpretations of combustion behavior are therefore grounded in physicochemical characterization data.