Water-in-diesel (W/D) emulsion is one of the promising alternative fuel that improves the combustion efficiency of a diesel engine and simultaneously reduces harmful exhaust emissions. To ensure a stable emulsion, surfactant is used during the formation of W/D emulsion which causes additional costs for this alternative fuel. A device called as Real-Time Non-Surfactant Emulsion Fuel Supply System (RTES) was invented to eliminates the use of surfactant and rapidly supply the W/D emulsion to the engine. The efficiency of 1-ton light-duty diesel truck fueled with W/D emulsion fuel produced by RTES was tested. Two types of the experimental method were used which chassis dynamometer testing and on-road are testing. The optimum water percentage and vehicle speed were evaluated from the result of exhaust emissions and fuel consumption measurement. Chassis dynamometer testing showed that the optimum water percentage for DE2 were 6.5% and vehicle speed aimed at 52 km/h was selected as the optimum vehicle speed. In on-road testing, the urban route gave the deficient results for both exhaust emissions and fuel consumption which agree with chassis dynamometer testing result where emulsion fuel is not suitable to be used at low speed vehicle operation.