Biogas for partial substitution of diesel in power generators

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.

In recent years, agricultural farms in Peru have started to implement equipment for anaerobic digestion of the organic residues of their production. At first, the main objective of the implementation was to obtain bio-fertilizers, but in this process, biogas was also obtained. Farms in Peru did not use this biofuel in any process, which is why they freed it or burnt it in torches, polluting the environment in both ways, due to the biogas content of methane. This last fuel has a high global warming potential (GWP) and carbon dioxide, result of the biogas burning is also a pollutant. In this context, an experimental device was designed and built to evaluate the performance of a Diesel cycle engine generator set of 40 kW using diesel and biogas as fuels. The generator set had a fixed speed of 1800 RPM. The tests were initially carried out using only diesel as fuel to obtain comparable parameters. The tests were made simulating an electric load of 62.5%. After this, a conversion kit was installed to allow the use of biogas in the engine. This equipment controls the Duty Cycle, which is a value between 0 and 1 that indicates the percentage of time the injectors are opened. The kit used as input signals the generated power, the electronic governor signal and the exhaust gases temperature. Then, tests were carried out partially substituting diesel for biogas. The biogas used for the test contained approximately 40% of methane. The results indicated that for higher Duty Cycles (higher quantities of biogas), the exhaust temperatures increased, due to the superior temperature of biogas combustion. With the percentage of methane available in the biogas, the substitution rates reached 17,9% and 36,7%, maintaining the generated power and reducing significantly the consumption of diesel. This technology makes possible the modular production of electric energy in agricultural farms, usually isolated, allowing the use of biogas commonly produced in the same place with the organic residues they manage, diminishing pollution, reducing costs and using the energy for useful purposes.