The objective of the present study refers to the examination of a diesel engine characteristics for various fractions of diethyl ether (DEE) as an oxygenated fuel additive in cottonseed oil biodiesel-diesel fuel blends. Firstly, several tests performed for diesel and B20 blend. Then, 2.5%, 5%, 7.5%, and 10% of DEE by volume was mixed with biodiesel-diesel fuel to prepare the ternary blends. All the fuel samples were run on in a single-cylinder, four-stroke, and direct-injection diesel engine at five different engine loads and fixed engine speed conditions. The experimental results showed that BTE was decreased by 17.39% while increasing in BSFC by 29.15% for 10% addition of DEE in the blend as compared to diesel fuel. Besides, the engine fueled with ternary blends revealed mitigation up to 12.89%, 4.12%, and 8.84% in the HC, smoke, and NOx emissions, on an average, respectively than those of diesel fuel. CO emission exhibited increasing trends with the diesel fuel at higher proportions of DEE despite up to 40.09% dropdown remarked for lower concentration at the maximum load. By the way, the CO2 also dropped under high loads. However, the combustion behaviors vaguely deteriorated when the CI engine run on all ternary blends. As a consequence, DEE can be evaluated as an auspicious aspect to remove the main issues with the usage of cottonseed oil biodiesel. It can be further highlighted that the addition of DEE up to 10% (by vol.) could be considered as a promising technique for the utilization of biodiesel/diesel blend efficiently in the CI engines without any major modifications.