Comparative evaluation and economic analysis of metal- and carbon-based nanoadditives in low-viscous waste-derived biofuel blends for diesel engines

This study presents a comparative evaluation of two distinct nanoadditives: a metal-based additive (copper oxide, CuO) and a carbon-based additive (carbon nanotubes, CNTs), focusing on their effects on engine performance and emissions when blended with a biofuel derived from pomelo peel waste (PWB) and conventional diesel fuel (CDF). The PWB bio-oil was extracted via thermal distillation, and a 30 % PWB + CDF blend (CDF30PWB) was further modified with 100 ppm of CuO and CNT nanoparticles. Characterization of CuO and CNT confirmed their catalytic potential for fuel enhancement. Results indicate that CDF30PWB improved brake thermal efficiency (BTE) by 6.09 % compared to CDF, while CNT and CuO further increased BTE by 1.63 % and 3.12 %, respectively. Brake-specific fuel consumption (BSFC) was reduced by 3.95 % for CDF30PWB, with CNT achieving an additional 3.69 % reduction and CuO lowering BSFC by 2.1 %. Emissions analysis showed that hydrocarbon (HC) and carbon monoxide (CO) emissions were reduced by 8.13 % and 2.61 %, respectively, for CDF30PWB, while CNT-enhanced fuel achieved further reductions of 14.59 % (HC) and 14.93 % (CO), and CuO reduced them by 4.29 % and 8.5 %, respectively. NOx emissions increased by 5.15 % with CDF30PWB, but CuO incorporation led to a 12.56 % reduction, and CNTs reduced NOx by 8.45 %. Smoke opacity was lowered by 9.88 % with CuO and 11.05 % with CNTs. Economic analysis highlighted that CuO achieved a 19 % potential cost reduction. This study concludes that CuO is more effective in NOx mitigation at a lower cost, while CNTs optimize engine performance and reduce HC and CO emissions.