During the past few decades, many researchers have proposed a partial replacement of Diesel in the Cl engine by substituting it with natural gas in order to reduce the exhaust emission without altering the performance characteristics of the engine too much. Most of these researches have focused on the combustion of natural gas in a dual fuel mode by using Diesel as the pilot fuel. However, the dual fuel,operation of natural gas with pilot Diesel reduces the brake thermal efficiency and increases the hydrocarbon emission. The present experimental work explores the potential of using CNG under dual fuel operation by utilizing two different blends of Diesel-ethanol-biodiesel as the pilot fuel. The present study reveals that the increased percentages of ethanol and biodiesel in the pilot fuel triggers an increase in the brake thermal efficiency of the engine. In this study, the NOx emission was also found to decrease with a corresponding increase in the percentages of ethanol and biodiesel in the pilot fuel. The study reveals definite encouraging aspects of using the D45E15B40 and D30E20B50 blends as the pilot fuel because it can extend the range of usage of the CNG to 9000 its of injection duration. (C) 2015 Elsevier Ltd. All rights reserved.