In this work, diesel engine emissions are studied by adding a cetane improver to the engine fuel. Dimethyl carbonate (DMC) additive is used as a cetane improver. A single‐cylinder, four‐stroke diesel engine is used to test the fuels. Three fuels are selected to run the engine, namely, biodiesel derived from neem oil + 1 vol% DMC (BD100 + 1DMC), BD100, and diesel. BD100 + 1DMC fuel emits a reduced amount of carbon monoxide and unburnt hydrocarbons compared to diesel under the same operating conditions of engine. The level of nitrogen oxides emission for BD100 + 1DMC is slightly higher compared to diesel and significantly lower compared to BD100.