NUMERICAL ANALYSIS OF BIOFUELS COMBUSTION IN DIESEL CYCLE INTERNAL COMBUSTION ENGINE

Resumo

Brazil has great dependence on the road transport sector, an important national integrator, whose fleet basically consists of vehicles powered by internal combustion engines of Diesel or Otto cycles. In 2014, the sector's fuel consumption was composed as follows: 47.1% diesel, 32.1% gasoline and 8.9% ethyl alcohol hydrate. Thus, dependence on non-renewable sources is evident and biofuels appear as an alternative to fossil fuels, and are gradually inserted into the national energy matrix, where biodiesel has become a highlight for compression ignition engines. Other promising sources emerge as, for example, sugarcane biofuels (diesel of cane and biodiesel of cane). It was proposed to use the numerical technique of Computational Fluid Dynamics to investigate the performance of a diesel cycle engine operating with sugarcane biofuels in a wide open throttle condition and to compare, in different engine rotation speed, the results to those obtained with diesel. The geometric domain constructed to represent the combustion chamber was reduced to a sector of 40º in order to reduce the computational effort and a simple injection strategy was adopted. For the description of physical phenomena such as turbulence, species interaction, ignition delay and fuel spray, suitable models were selected. Analyzing the results it was inferred that the modeling made good prediction of phenomena such as the average ignition delay and variables such as evolution of mean pressure, mean temperature and accumulated heat release as a function of the angle of rotation of the crankshaft. The biofuels surrogate represented them adequately; however, the surrogate of diesel did not adequately represented it. The highest pressures inside the chamber occurred at 1600 rpm, coinciding with the real engine speed characteristic. It was concluded that the fluid dynamics modeling applied to engines is an alternative to the experimental tests, providing results hard to obtain experimentally.