Simulation Study of Force Distribution in the Multiple Linkage System of a Spark Ignition Engine Operating in the Atkinson Cycle

The tests were carried out on an 3D engine model with an unconventional multiple linkage system. Compared to a classic crankset, the mechanism consists of more elements. In this multiple linkage system the camshaft, the piston rod and the main rod are connected to one common element. The camshaft rotating during operation at twice the speed of the crankshaft makes possible to achieve different piston stroke lengths with each revolution. With proper synchronization of the camshaft revolution with the crankshaft, the suction and compression stroke is smaller in relation to the expansion and exhaust strokes. For this reason, the Atkinson cycle was obtained without interfering with the variable valve timing. The thermal cycle is characterized by increased theoretical thermal efficiency. Due to the unique mechanism, the piston movement has different characteristics compared to classic solutions. Therefore, work was undertaken to analyze the distribution of forces in the system. For the needs of the work, a 3D model of the described engine was created. It was used to examine the characteristics of the piston path during operation. Using computer simulation, piston movement and forces occurring in the system were analyzed. Numerical simulations of combustion process were also carried out in a program designed for internal combustion engines. The most important thermodynamic indices such as pressure distributions, temperatures and heat release are presented. Identical tests were also carried out for the engine with a conventional crank system. The results of both engines were combined and analyzed.