Recently, Jatropha, a fast growing tropical plant, has caught the attention of researchers because the oil produced from Jatropha is a non-edible. However, worse emissions, when using raw Jatropha oil in diesel engines, have been reported in the literature due to its higher viscosity and lower volatility. Therefore, it is necessary to find some way to reduce the emissions of diesel engines. In the present research, experiments have been designed and performed to study the effects of Jatropha hydrogen peroxide emulsion on combustion, performance, and the emission characteristics of a diesel engine. Hydrogen peroxide in a solution of water at a concentration of 30% was used for making the emulsions with mixing mass ratios of 5%, 10%, and 15%. A single cylinder, four-stroke, high speed, direct injection diesel engine was used for the experiments. The acquired data were analyzed for various combustion parameters such as in-cylinder pressure, ignition delay, ignition duration, heat release, for performance parameters and emissions of CO, CO2 (carbon dioxide), HC, NOx, and PM as well. While running the engine on the Jatropha hydrogen peroxide emulsion fuel, improvements in performance and emissions were found and the optimum mixing ratio of the solution with hydrogen peroxide was 15%. (C) 2014 Elsevier Ltd. All rights reserved.