Fostering sustainable energy in India is vital for economic growth. Collaboration among environmentalists, humanitarians, and scientists is essential to address growing demands. With fossil fuel depletion a concern, exploring alternative fuels like biodiesel is crucial. Biodiesel performs similarly to conventional diesel, making its integration for energy sustainability a pragmatic choice. Utilizing a numerical simulation tool, this study assesses the performance and emission parameters of a diesel engine powered by blends of waste-cooking oil biodiesel (WCO10, WCO20, WCO30, and WCO100) at various engine speeds (1500, 2000, 2500, and 3000 RPM) and these outcomes also compared with conventional diesel fuel. These findings emphasize the critical role of RPM management and the strategic composition of blends in mitigating emissions. Though particular blends may closely mimic diesel in terms of performance and emissions in specific facets, the pattern of reduced efficiency and fuel consumption at higher RPMs remains consistent across all WCO blends, including pure diesel, and higher RPMs also align with elevated emission levels. This approach aims to achieve an optimal balance between engine performance enhancement and the utilization of alternative fuel sources such as WCO blends.