Performances and Emissions of a Small Size Diesel Powered Generator Fueled with Vegetable Oil and its Water-in Emulsions

Diesel engines are worldwide used in the transport, electricity generation and shaft power and they burn oil products which can be partially or totally replaced by alternative fuels, such as vegetable oils. Vegetable oils have physical characteristics close to those of diesel oil and as they are of plant origin, they have the potential to significantly reduce CO2 emissions into the atmosphere. Nowadays fuelling compression ignition engine with vegetable oil is a feasible solution, with a relevant number of working plants, mainly for medium size electric generators; not the same can be told about small size diesel generators. Few marine propulsion examples are also reported. In this paper, a rapeseed oil and some its water-in emulsions, in different percentage 5, 10 and 15% v/v, have been fuelled in a small size Diesel engine used as power generator in a co-generation system. Tests were conducted in a naturally aspirated Scania DC09 direct injection four-stroke 250kW, 5-cylinders, 9.3 dm3 displacement Diesel engine from low load to 120kW as load conditions. Emulsions were produced on site by a device that adds steam to vegetable oil, so continuously feeds the engine with emulsified oil at about 60°C; tests were also carried out with sample emulsions made offline with an ultrasonic device. Gaseous (CO, HC, NO/NOx, CO2) and particulate emissions have been characterized in steady state conditions. CO, HC and particulate emissions are strongly reduced by fuelling vegetable oil emulsions compared to commercial diesel fuel. NOx emission are not significantly affected, rather a small increase is observed in some conditions; authors believe that an engine optimized for reducing NOx with diesel oil requires a different injection tuning, not feasible during the experiments.