Reactivity Controlled Compression Ignition (RCCI) combustion has been established by modification of intake of a diesel engine. Studies were carried out on the existing engine with Conventional Diesel Combustion (CDC) and performance and emission parameters were recorded. Cotton seed biodiesel (COME) as low reactive fuel was injected into inlet manifold through a port fuel injector and diesel as high reactive fuel is injected in the cylinder through direct injection. Modified engine was tested for performance and emission characteristics. Simultaneous reduction in NOx and smoke emissions were observed with introduction of COME. CO2 emissions decreased marginally and unburnt hydrocarbons (UHC) decreased at lower percentages of COME and increased with higher percentages of COME. An increase in the Brake Thermal Efficiency (BTE) of the engine is observed at all loads. Exhaust Gas Temperature (EGT) and Brake Specific Fuel Consumption (BSFC) are lower in RCCI mode as compared to CDC. The optimum operating range of COME is observed with 10-20% of COME, which has 22% of average decrease in NOx and 30% decrease in the smoke emissions. (C) 2018 Elsevier Ltd. All rights reserved.