COMPARATIVE STUDY OF THERMAL CALCULATIONS OF AN OTTO CYCLE INTERNAL COMBUSTION ENGINE WITH RESULTS OF EXPERIMENTAL TESTS

Resumo

Conduct experimental trials during a research is a process that demands time and financial resources, being important the use of tools such as computer programs or theoretical calculations methodologies that allow to find results closer to the real ones, there for representing a reduction of time and cost of the research. In the development of engines, studies of the thermodynamic cycle through the pressure curve inside the cylinder are of fundamental importance for the analysis of the combustion process. This work presents an evaluative and comparative study between the thermal calculation of an internal combustion engine, with results obtained from simulations in the Siciclo software and with results obtained from experimental tests. The thermal calculation is based on the First Law of Thermodynamics and it was developed on a spreadsheet. The Siciclo is a software developed in an academic environment, which consists of the simulation of the pressure and temperature curves inside an engine from an imposed combustion law and through solution of the First Law of Thermodynamics. The experimental tests were performed on a test bench, consisting of a single cylinder engine instrumented with a pressure transducer, a crank angle encoder and thermocouples, coupled to a hydraulic dynamometer. The pressure curve inside the combustion chamber and the external speed characteristic curve obtained by each method were compared, aiming to verify the accuracy of the theoretical and simulated results in relation to the actual results. The thermal calculation overestimated the maximum pressure by 44%, mainly due to the consideration of instantaneous combustion at constant volume, while the Siciclo, mainly by adopting the Wiebe burning law, overestimated the maximum pressure by only 2%. From the pressure data, analyzes justifying the differences in the external speed characteristic curve were made.