Geometrias para uso de ciclo super-expandido em motor de combustão interna

Abstract

The evolution of internal combustion engines is the development of world society, which presents us with better engines, more efficient, more economical and less polluting to the environment. Due to these factors, the use of over-expanded engines has been gaining space automotive scene. An idea proposed by Atkinson in the XIX century, which defines overexpanded engines that have a better thermodynamic efficiency when compared to Otto engines, because they have a higher expansion ratio than the compression ratio. This work brings different suggestions on how to turn Otto cycle engines, very common on the national industry, into Atkinson cycle engines. This work offers some geometries, which have an auxiliary piston that displaces through a cylinder attached to the motor that causes it to operate in the Atkinson cycle due to a fully synchronized movement of its mechanisms. In search of a compact and easy-to-fit solution that brings Atkinson values equal to, or greater than, 1.4 and has immediate responsiveness, it is the basis of new volumetric forces of an engine coming from the auxiliary piston movement, so that there is an evolution in the results of the proposed concepts as the research progresses. The final model is compatible with a performance ratio higher than 1.4, by adapting a header with the pent-roof format and replacing the original piston with a dome piston, being able to implement a 58mm auxiliary cylinder in this kind of head. With a 56 mm stroke, the auxiliary piston moves into the combustion chamber of the engine at a fraction of 50% of the stroke value. The auxiliary piston movement has half the frequency of the main piston, the movement is performed due to a connecting rod that connects to a crankshaft next to the cylinder head. This crankshaft is driven through a pulley twice the original pulley’s diameter, where both are interconnected through a toothed belt. The engine was dimensioned based on a 1.6-liter VW AP engine, being able to be retrofitted into other engine models.