Application to micro-cogeneration of an innovative dual fuel compression ignition engine running on biogas

Abstract

• A CI dual fuel engine running on biogas is optimized by experiments and simulation. • The engine is optimized for a mid-size farm, requiring a micro-cogeneration system. • The farm can self-produce all the biogas, becoming almost energy independent. • The proposed engine is 20% more efficient than a corresponding SI biogas engine. • Cogeneration + biogas provide a net actual value after 15 years of 1340 k€. Renewable sources and enhancement of energy conversion efficiency are the main paths chosen by the European Community to stop climate changes and environmental degradation, and to enable a sustainable growth. For this purpose, the construction of a new and more dynamic electricity distribution network is mandatory. This “smart grid” should also include small and medium-size companies, able to program the generation and use of energy from renewable sources (the so-called "prosumers"). In this frame, micro-cogeneration (rated electric power up to 50 kW) is one of the most promising techniques. In this work, the application to micro-cogeneration of an innovative Compression Ignition internal combustion engine, operated in Dual Fuel mode is proposed. Thanks to the specific combustion system (Reactivity Controlled Compression Ignition, RCCI: a lean homogenous mixture of air and biomethane or biogas is ignited by the injection of a small amount of Diesel fuel), brake thermal efficiency can be increased at all operating conditions, compared to a conventional Spark Ignition engine running on biomethane or biogas. The ensuing reduction of CO 2 emissions is higher than 20%. Furthermore, the proposed engine can tolerate larger variations in the composition of the biogas, without a significant drop of thermal efficiency. Finally, in case of emergency, it is able to run on Diesel fuel only. The use of the engine is particularly suitable for a company operating in the agricultural field, such as a mid-size farm, that is able to produce biogas for its self-consumption. Therefore, a representative study case is selected, and the corresponding electrical and thermal energy needs are analysed throughout a typical year. The energetic analysis leads to the identification of the most suitable engine size and calibration settings, in order to reduce the purchase of electricity and natural gas, maximizing the use of the company's own renewable sources (biogas or biomethane). The final goal of the optimization process is to create a virtuous system, that can reduce the environmental impact and make the company almost independent from the energetic point of view.