This SBIR Phase I project will develop a water separator media to protect heavy duty engines from the water content in modern ultra low sulfur diesel fuels. The ultra low sulfur diesel fuel typically found in the field has very low interfacial tension allowing water to be present in the form of very fine droplets which pass through conventional water separators and end up in the fuel injection system. This project will quantify and develop a functionalized multiwall carbon nanotube-based water separator to be used with all ultra low sulfur diesel fuels on the market with nearly 100% water removal efficiency. The objective is to enhance the separator performance to cost ratio by working to further increase the separation efficiency and lower the media cost through process scaling and materials development.<br/><br/>The broader impact/commercial potential of the project are focused on benefits related to enhanced ultra low sulfur diesel fuel separation, including more consistent fuel delivery to the engine, longer injector/engine life, better combustion of ultra low sulfur diesel fuel, lower maintenance costs, new jobs enabled by the use of high-sulfur fuel reserves, and more efficient combustion of bio-fuels. Reduced water content in the fuel will help to improve performance of the high pressure fuel injection systems, maintain tolerances of the fuel injection system components, and reduce maintenance costs.