This paper investigates the diesel engine performance and exhaust emissions with biodiesel as fuel and diethyl ether (DEE) as additive. Sunflower methyl ester was selected as a base fuel for the engine and DEE as an oxygenate with varying percentages. The experiment was conducted on a single-cylinder naturally aspirated direct-injection diesel engine with constant speed. Engine emissions are one of the major sources of pollution in the atmosphere. An approach to solve this problem is to add oxygenates to biodiesel. In this research work, an attempt has been made to analyze the effect of diethyl ether as an additive. Parameters such as brake thermal efficiency, brake specific fuel consumption and exhaust emission of CO, CO<inf>2</inf>, HC, NO<inf>x</inf> and smoke intensity were measured, and significant improvements were observed with the addition of diethyl ether with biodiesel as a blend. The brake thermal efficiency of biodiesel varied from 11.91 to 20.9%. NO<inf>x</inf> emission was reduced from 469 to 261 ppm in full load. Hydrocarbon (HC) varied from 200 to 130 ppm in full load. Similar variations were inferred for other emissions also. © 2019 Elsevier B.V., All rights reserved.