Emulsions of diesel and water are often promoted as being able to overcome the difficulty of simultaneously reducing emissions of both oxidises of nitrogen (NOx) and particulate matter from diesel engines. In this work, the performance of an engine together with its effect on environment were tested when engine was powered by both pure diesel and emulsified fuel with various quantities of water content in the diesel fuel. The amount of water quantities added ranged between 5% and 30% by volume. The engine speed during the experimental work was within the range from 1000 to 3000 rpm. While producing similar or greater thermal efficiency and improved NOx emission outcomes use of the emulsion also results in an increase in brake specific fuel consumption. It was also found that, at high amount of water addition, the nitrogen oxide decreases. Also, in general, the diesel emulsion fuel emitted an amount of CO2 higher than that of pure diesel. (C) 2009 Elsevier Ltd. All rights reserved.