A comparative assessment of combustion behaviors, thermo-exergetic sustainability and emission characteristics of a CI engine fueled with hybrid co-pyrolytic fuel blends

Amidst growing environmental concerns and the urgent need to decarbonize transport, this study investigates the potential of co-pyrolytic biofuels derived from waste biomass and plastics as sustainable alternatives to fossil diesel. Thermo-catalytic co-pyrolysis of Azadirachta indica and Pongamia pinnata seeds with low-density polyethylene (LDPE) was conducted using Al 2 O 3 and CaO catalysts, yielding maximum liquid fuel outputs of 93.91% (CB1) and 92.5% (CB2) at 500 °C with 10 wt% catalyst. The resulting fuels exhibited favorable properties, including high calorific values (44.42–44.86 MJ/kg) and low densities (794–797 kg/m 3 ). Blends of these fuels with diesel at 10%, 20%, 30%, and 40% (v/v) were evaluated in an unmodified single-cylinder compression ignition (CI) engine for combustion, emission, energy, and exergy performance at 1500 rpm and a compression ratio of 18:1. Experimental results demonstrated that blends, particularly 20% and 30%, enhanced brake thermal and exergetic efficiency while reducing CO, HC, and smoke emissions compared with neat diesel. The oxygenated nature of the co-pyrolytic fuels contributed to more complete combustion, especially at higher loads where CO emissions were decreased to 0.01 vol%, HC emissions showed measurable reductions across all blends, and smoke opacity reached a minimum of 24.5% for the 90D10CB2 blend. These improvements were attributed to better ignition characteristics, improved air–fuel mixing, and higher oxygen content in the blends. Overall, the study confirms the viability of waste-derived co-pyrolytic fuel blends as efficient, cleaner-burning alternatives for CI engines without modifications, aligning with circular economy goals and offering a promising route for sustainable fuel development. • Production of sustainable fuels obtained from catalytic co-pyrolysis of Azadirachta indica and Pongamia pinnata seeds with LDPE, using Al 2 O 3 and CaO catalysts. • Blends of co-pyrolytic fuels with diesel at 10%, 20%, 30%, and 40% (v/v) were prepared and characterized. • Engine test for combustion, emission, energy, and exergy performance using different fuel mixtures under variation of load conditions and fuel blends. • Co-pyrolytic fuels enhance the combustion process and also reduce pollutant emissions, especially under partial and full-load operations. • Co-pyrolytic fuel blends offer a sustainable, efficient, and cleaner-burning alternative to conventional diesel.