A hybrid entropy-VIKOR-Taguchi approach for sustainable optimization of diesel engine performance and emissions

The urgent demand for sustainable transport fuels highlights biodiesel-hydrogen dual-fueling as a promising pathway to improve engine efficiency while reducing carbon-based emissions. Nevertheless, optimizing combustion parameters to balance performance with stringent emission constraints remains a major challenge. This study introduces a hybrid Entropy-VIKOR-Taguchi framework to optimize the performance, combustion, and emission characteristics of a compression-ignition engine operating on a cottonseed biodiesel (B20)- hydrogen blend. The methodology integrates entropy-based weighting for objective parameter prioritization, VIKOR for compromise decision-making, and Taguchi design for efficient experimentation, thereby minimizing trial costs and enhancing reproducibility. Experiments evaluated three key parameters, namely injection pressure (200-240 bar), compression ratio (16.5-18.5), and hydrogen flow rate (10-20 L/min). Results showed that hydrogen enrichment improved combustion, with peak pressure reaching 85 bar and a maximum heat release rate of 86 J/deg. Engine efficiency increased to 33.52% BTE and a minimum BSFC of 0.213 kg/kWh, while emissions decreased (HC = 65 ppm, CO = 0.016%). However, NOx rose to 1380 ppm at high hydrogen flow, underscoring the trade-off between efficiency and emissions. The optimal condition, IP = 240 bar, CR = 17.5, and H2 = 10 L/min, yielded the lowest VIKOR index (Q = 0.0588), ensuring balanced sustainability. This framework offers a transferable optimization pathway for dual-fuel engines, supporting decarbonization targets under SDG7 and SDG13.