Analysis of the Technical Viability of Biogas Utilization in Compression Ignition Engines for Electric Power Generation

摘要

Increased energy demand and security of energy supply have become a concern in recent decades due to strong industrial growth. The high cost of fossil fuels and the need to reduce the emission of greenhouse gases have made renewable energy sources an attractive object. In this context, biomass becomes interesting and is the second largest source of renewable energy in Brazil, possessing many characteristics similar to fossil fuels. Energy can be obtained by direct burning or by conversion into biofuels, such as biogas, which is composed primarily of carbon dioxide and methane. Methane released directly into the atmosphere has 21 times the greenhouse effect potential of CO_2. In this way the importance of the development and improvement of this fuel and of the converter machines, which play a fundamental role in the transformation of biomass into other forms of energy, is justified. This study aims at analyzing the technical viability of application of biogas in compression ignition engines for electric power generation in RCCI operation mode (Reactivity Controlled Compression Ignition) and dualfuel by fumigation. The experimental part was started with the survey of the data of the operation of the engine in conventional (diesel) combustion mode, the fuel used was the diesel S10. As the proposal was the generation of energy by means of generators, the engine speed was maintained constant at 1800 rpm and the load conditions were varied between IMEP 3 bar, 6 bar and 8 bar. The temperature of the engine oil and cooling was maintained at 90 ± 5°C (usual temperature in the generators). Subsequently the tests were repeated following the same previous conditions, however, the injection of the gaseous fuel at the intake was done, thus operating in dualfuel mode combustion. The results showed that there are no penalties relative to the performance of the engine, the values of torque and power were maintained for the two models of dualfuel mode combustion. Substitution values were higher than 94% at medium and high loads, and higher than 56% at low loads. Regarding the brake efficiencies, higher values were obtained in medium and high loads for the two combustion methods, with few changes in low loads. Regarding the production of electricity through biogas, the operation in dualfuel mode by fumigation can bring a 36.5% higher economy in medium and high loads, when compared to conventional combustion. Already in RCCI this economy is achieved only in medium loads.