This study investigated the combustion characteristics of an engine fueled by BD25% (Pongamia biodiesel) blended with water (5, 10%, and 15%) and 1% Span80 emulsions. The findings were compared to those obtained from biodiesel fuel. The primary goal of this study is to employ water addition as a means to alleviate the detrimental effects caused by a significant decrease in NOx and smoke emissions compared to HC and CO. To achieve a highly uniform emulsified fuel mixture, the following compositions are used: Diesel, 25% BD, Water, and Surfactant Span 80. The proportions of these components are as follows: D69:B25:W5:S1 (EBD1), D64:B25:W10:S1 (EBD2), and D59:B25:W15:S1 (EBD3). These solutions are mechanically agitated for approximately 45 minutes. By retaining the mixture in a beaker for 48 hours, the stability of the emulsified fuels was examined, and it was found that there was no dissolution of the water from the fuel. Experiments were conducted on a diesel engine under various loads using diesel, BD25, EBD1, EBD2, and EBD3 fuels. The outcomes showed that compared to the 25% biodiesel blend, NOx emissions from the engine using EBD3 emulsified fuels were drastically reduced by 47.25%. However, compared to the BD25 blend, the EBD3 fuel showed an increase in CO and HC emissions by 28.6% and 32%, respectively. © 2024 Elsevier B.V., All rights reserved.