VIBRATION ANALYSIS ON THE CRANKSHAFT AXIS OF AN INTERNAL COMBUSTION ENGINE Claudio Marcio Santana 1 , Jose Eduardo Mautone Barros 1 , Helder Alves de Almeida Junior 1 e Jorgimara de Oliveira Braga 1 . Federal University of Minas Gerais – Av. Antonio Carlos, 6627, Pampulha, Belo Horizonte – CEP: 31270-901. claudiowsantana@gmail.com; mautone@demec.ufmg.br; helder.alves.eng@gmail.com; jmarabraga@hotmail.com RESUMO Vibration problems in internal combustion engines produce premature wear on the internal components of the engine, which contributes both to reduce the lifespan of the engine itself as well as cause discomfort to the occupants of the vehicle. Thus, since it is impossible to totally eliminate vibrations from engines, it is important to understand the sources of vibration production and control them to acceptable levels. The general objective of this paper is to measure the vibration in the areas that undergo greater efforts due to the processes of combustion and mechanical forces. These areas are the fixed bearings located to the extremes of the crankshaft. The specified objective of this study is to correlate these levels of crankshaft engine vibration relative to the fuel used, ethanol and gasoline, and assess the influence of lubricant oils on the vibration levels as a function of the viscosity of the lubricant. The results demonstrated that the vibration intensity of the engine increases with increasing engine speed and load. In all operating conditions, the ethanol-run engine has higher vibration intensities than the gasoline-run engine. For the same type of fuel, an oil of higher viscosity attenuates the level of vibration of the engine. Measurements show an average increase of 18% of transverse vibration and 12% of longitudinal vibration in the crankshaft of the engine running on ethanol in relation to gasoline with low viscosity lubricant and 14 % and 10 % with higher viscosity lubricant. INTRODUÇÃO Internal combustion engines are classified according to the burning mode of the fuel in both spark-ignition and compression-ignition engines [1]. Both gasoline and ethanol-powered engines are examples of spark-ignited engines. Thus, the firing of the fuel is initiated with a spark provided by the spark plug [2]. Diesel engines typically run on diesel oil or a blend of diesel and biodiesel. The combustion in these engines occurs spontaneously, due to the air- fuel mixture under high pressures and temperatures inside the cylinder [3]. Viscosity is the main property of automotive lubricant oils for internal combustion engines and it also indicates the degree of resistance a lubricant oil allows on two surfaces in relative motion. Lubricant oils undergo changes in their viscosity when subjected to temperature variation and load and these variations can be very different depending on each type of lubricant oils. The SAE nomenclature with two numerical viscosity values indicates that this lubricant is multi-