Energy, exergy and exergoeconomic analysis of a CI engine fuelled with waste frying oil biodiesel blended with waste tyre pyrolysis oil and higher alcohols (Heptanol and Octanol): A waste-to-energy approach

This study evaluates a waste-to-energy diesel concept that co-valorises waste cooking oil and end-of-life tyres by formulating biodiesel–tyre pyrolysis oil blends with small additions of higher alcohols (1-heptanol and n-octanol). Five fuels (B100, B90T10, B85T10H5, B85T10O5 and B80T10H5O5) were tested in a single-cylinder diesel engine. Engine performance, emissions and combined energy–exergy–exergoeconomic indicators were used to assess thermodynamic and economic viability. The quaternary blend B80T10H5O5 achieved the highest mean energy and exergy efficiencies (26.5 % and 24.6 %) and reduced brake-specific fuel consumption by about 5 % relative to neat biodiesel, owing to improved volatility and fuel oxygenation. This benefit was accompanied by higher NOx emissions and the largest specific exergy cost (≈1430 USD GJ−1) at full load. By contrast, the binary blend B90T10 preserved biodiesel-like efficiency while lowering the specific exergy cost of shaft power by roughly 10 %, emerging as the most cost-effective option. Overall, modest shares of tyre pyrolysis oil (10 %) and long-chain alcohols (≤5 %) in waste-oil biodiesel can provide an attractive compromise between energy efficiency, emissions and exergy-based cost, supporting circular-economy-oriented diesel combustion.