Abstract Vegetable oils are a potential alternative to the partial or total substitution of diesel fuels. An experimental investigation is conducted to evaluate the effects of using ethanol and diethyl ether as additives to biodiesel/diesel blends on the emission and performance of direct injection unmodified diesel engine. Biodiesel was made by pyrolysis process. Cashew nut shell liquid (CNSL) was selected for biodiesel production. The fuel containing 20% biodiesel and 80% Number 2 diesel fuel, is called here as B20, 90% B20 and 10% ethanol by volume is called B20+E10 and 90% B20 and 10% diethyl ether by volume is called B20+D10. The effect of test fuels on engine torque, power, brake specific fuel consumption, brake thermal efficiency, exhaust gas temperature, were ascertained by performance tests. The influence of blends on CO, CO2, HC, NO and smoke opacity were investigated by emission tests. The experimental results showed that the exhaust emissions for 10% diethyl ether with B20 were fairly reduced, especially the NO is reduced remarkably by 51% while comparing diesel. B20+D10 blend reflect better engine performance and lower emissions than B20+E10and B20 blends.