Comparative Evaluation of Binary and Ternary Diesel–WTPO–n-Butanol Blends in a Single-Cylinder DI Diesel Engine: Relevance to Sustainable Waste Tire Valorization

Waste tire pyrolysis oil (WTPO) offers a route for waste valorization, but its use in com-pression ignition engines is limited by unfavorable fuel properties. This study compares performance, combustion, and emission characteristics of 80 vol.% diesel-based blends containing refined WTPO, n-butanol, or both. The WTPO was a purified, vacuum-distilled fraction of the liquid tire-pyrolysis product. Experiments were conducted at 3000 rpm un-der nominal electrical loads of 250–1250 W using neat diesel (D100), 80 vol.% diesel/20 vol.% WTPO (D80WTPO20), 80 vol.% diesel/20 vol.% n-butanol (D80B20), and 80 vol.% diesel/5 vol.% WTPO/15 vol.% n-butanol (D80WTPO5B15). At 1250 W, D80WTPO20 exhibited 8.1% higher specific fuel consumption and 5.4% lower system-efficiency index based on nominal electrical load than D100. D80WTPO5B15 showed 5.4% higher specific fuel consumption, while its system-efficiency index was statistically comparable to that of D100 and significantly higher than that of D80WTPO20. It also exhibited significantly lower CO and NOx concentrations than D80WTPO20 and significantly lower HC concentration than D80B20. The n-butanol-containing blends exhibited longer SOI–CA10 intervals and higher premixed heat-release peaks than D100. Unlike the previously reported ternary diesel–WTPO–n-butanol study, this work includes corresponding binary reference blends at the same diesel fraction and jointly evaluates performance, emissions, smoke-opacity, in-cylinder pressure, heat release rate, and combustion phases. From a sustainability perspective, this formulation-level comparison supports the assessment of refined WTPO utilization as a waste-to-energy and circular-economy pathway, while highlighting the associated performance and exhaust-gas trade-offs.