Diethyl ether and n-butanol, when added to diesel, increase the oxygen content and cetane number of the fuel. This results in smoother combustion in compression ignition engines. Blending diesel with up to 15% of both diethyl ether and n-butanol increases the cetane number compared to commercial diesel. Biodiesel, derived from coconut oil and containing higher oxygen content, enhances combustion characteristics in diesel engines due to its structure. Testing involved blending diesel with coconut oil biodiesel at 20%, 30%, and 50% (volume basis) along with additions of 10–15% (volume basis) of n-butanol and diethyl ether. The 20% biodiesel blend with 15% n-butanol resulted in the least unburnt hydrocarbon (28 ppm) and low carbon monoxide emissions (~0.02%) at full load. The 30% biodiesel blend with 15% n-butanol achieved maximum efficiency (~33%), which is 24% higher than that of diesel at full load. This blend also showed lower NOx emissions (333 ppm), which was significantly less than emissions from pure diesel (~115 ppm reduction).