Waste utilization is found to be challenging task all around the globe. Converting waste into useful form energy was found as a significant landmark in meeting the demand of world energy requirement. Thus an attempt was made in this study to make use of Waste Cooking Oil (WCO) which degrades both the environment and human health as fuel to operate compression ignition engine and investigate its performance, emission and combustion behavior. One time used cooking oil was collected from the hostel mess of author institution. In the first phase of the study, single cylinder water cooled diesel engine was developed as test engine and operated in a single mode with neat diesel and waste cooking oil as fuel. Test engine was operated under various load condition and the readings were observed. Same engine was modified in the second phase of the work to operate in duel fuel mode with a low reactive fuel like ethanol as primary fuel. In this work ethanol was injected instead of inducting in the intake manifold with the help newly developed electronic primary fuel injection system.Newly developed injection system is compact and cost effective. It also helps in accurate metering of primary fuel with high degree of repeatability. Experiments were conducted at various loads and at different ethanol energy share. It was inferred that at part load condition neat diesel and WCO produced a brake thermal efficiency of 24.2% and 22.0% respectively. Oxides of nitrogen emission was found to be 291 ppm and 178 ppm with neat diesel and WCO respectively. Smoke emission was recorded as 36% with diesel fuel whereas it was around 66% with neat WCO. However on injecting ethanol with the help of newly developed injection system, improved the brake thermal efficiency of neat WCO to 22.4% at the ethanol energy share of 30%. Oxides of nitrogen emission was found to be marginally high and smoke emission was reduced drastically with the ethanol injection at the part load condition. Thus with the help of developed electronic injection system WCO can be used effectively in the part load condition as fuel in compression ignition engine with NOx reducing techniques in the future for producing clean and green energy.