Selection of Optimal Waste Cooking Soybean Oil Biodiesel Blends for Emission Reduction in CI Diesel Engines Under Variable Loads: A Combined Analytic Hierarchy Process (AHP)-Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) A

Globalization has significantly heightened the demand for fossil fuels, resulting in a notable increase in ozone pollution levels. This heightened environmental awareness has spurred researchers to delve into the exploration of diverse renewable energy sources. In the course of extensive investigation, this study investigates the emission characteristics of a diesel engine fueled by waste-cooking Soybean oil biodiesel and diesel blends. A single-cylinder, four-stroke CI engine was utilized to experiment with various biodiesel blends, assessing major regulated pollutants at 25%, 50%, 75%, and 100% loads. Different Blends like B10WCO, B20WCO, B30WCO, B40WCO, B50WCO, and B0 Diesel Blends were prepared and ranked using an AHP-TOPSIS hybrid MCDM approach to determine the optimal fuel. AHP was employed to assess each criterion's importance, while TOPSIS ranked the alternatives. NOx emerged as the most significant criterion, with a 30% Waste Cooking Soybean oil biodiesel and 70% diesel blend identified as the best option at 75% and 100 % engine loads. Policymakers can use this integrated analysis technique to develop new business models aimed at reducing exhaust emissions and fossil fuel reliance. This research contributes to the study of renewable energy sources, particularly Waste cooking Soybean biodiesel blends, in automotive usage, providing insights for more efficient and environmentally balanced alternatives.