Different methods to improve the performance of a WCO (waste cooking oil of sunflower based) mono cylinder compression ignition (CI) engine were investigated. A single cylinder direct injection diesel engine developing the power output of 3.7 kW was used. Initially the engine was tested with neat WCO as fuel. WCO was then 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 were used as pilot fuels. 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. Neat WCO resulted in reduced brake thermal efficiency, increased smoke, hydrocarbon and carbon monoxide emissions at both power outputs. The maximum thermal efficiency was observed as 26% and 30.5% respectively with neat WCO and neat diesel at 100%. The smoke emission was found as 70% and 40% respectively with neat WCO and neat diesel at 100% load. WCO emulsion indicated considerable improvement in engine’s performance. The brake thermal efficiency was achieved as 28% with WCO emulsion at 100% load. The smoke and NOx values were noted to be less than neat WCO. However WCO emulsion showed inferior performance at 40% load. Oxygen enrichment further improved the engine’s performance with significant reduction in smoke, hydrocarbon and carbon monoxide emissions with neat WCO and WCO emulsion as fuels at both loads. 24% of oxygen concentration was found to be optimal for best operation for both WCO and WCO emulsion. At 24% of oxygen enrichment the brake thermal efficiency was achieved as 28.4% and 29.6% respectively with neat WCO and WCO emulsion as fuel at 100% load. However, NOx emission was found to be higher with oxygen enrichment as compared to ambient oxygen concentration. Hydrogen induction in dual fuel operation raised the brake thermal efficiency further with WCO and its emulsion as pilot fuels with 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. 24% oxygen concentration by volume could be recommended for optimal operation with WCO and its emulsions as fuel.