Different methods to improve the performance of a WCO (waste cooking oil of sunflower) based mono cylinder compression ignition (CI) engine were investigated. Initially WCO was converted into its emulsion by emulsification process and tested as fuel. In the second phase, the engine intake system was modified to admit excess oxygen along with air to test the engine with WCO and WCO emulsion as fuels under oxygen enriched environment. In the third phase, the engine was modified to work in the dual fuel mode with hydrogen being used as the inducted fuel and either WCO or WCO emulsion used as the pilot fuel. All the tests were carried out at 100% and 40% of the maximum load (3.7 kW power output) at the rated speed of 1500 rpm. Engine data with neat diesel and neat WCO were used for comparison. WCO emulsion indicated considerable improvement in performance. The smoke and NOx values were noted to be less than neat WCO. Oxygen enrichment further improved the engine’s performance with significant reduction in emissions with neat WCO and WCO emulsion as fuels. Hydrogen induction in dual fuel operation raised the brake thermal efficiency further and reduced the smoke, HC and CO emissions. It was concluded that WCO could be effectively used as fuel in a single cylinder diesel engine by making stable emulsion with water and ethanol. Oxygen enrichment could offer considerable improvement in BTE, significant reduction in smoke, HC and CO emissions at all power outputs with neat WCO and its emulsion as fuels. Induction of a small amount of hydrogen in dual fuel mode could improve the performance of the engine further using WCO and its emulsion as fuel.