Synthesis of a variable stroke slider crank mechanism for a reciprocating internal combustion engine

Abstract

From its inception, the internal combustion engine has evolved in small and sometimes great leaps, driven by constructive, technological and exploitation implementations that have allowed it to meet consumer expectations as well as environmental and fuel consumption regulations. Spark ignited engines have lower performance under low loads compared to Diesel engines, the biggest difference between them being the compression ratio, limited in the first ones by the risk of the detonation occurrence. The introduction of mechatronics developments in spark ignited engines have contributed to their performance improvement through the 5128 Edison Henao Castañeda et al. controlled variation of ignition and valve events (timing and lift), controlled variation of intake manifold length and volume, exhaust gas recirculation, and variable supercharging systems, among other technological strategies. Of all the constructive alternatives, the biggest impact on engine performance lies in compression ratio, and the control of its variation becomes one of the main research goals for engine manufacturers. In this paper, some of the constructive efforts, reported in literature, to obtain mechanisms and systems for the control of compression ratio of internal combustion engines are overviewed, with the main goal of presenting the methodology for the optimized synthesis of a multi-link variable compression ratio mechanism, designed to be assembled in a commercial single cylinder stationary Diesel engine as a fundamental equipment of an octane rating test bench for different fuel blends tested. The synthesis technique presented in the paper develops the range of motion for the six links Stephenson mechanism, applies a method of synthesizing the output slider trajectory, and analyzes the mechanism performance in terms of slider stroke variation range. It is shown that compression ratios resulted from slider variations can be kept between 10 and 17,5, a range sufficient to study commercial engine fuels, a utilitarian goal pursued.

Kinematics modeling of the gear-based crank mechanism engine regardless of the compressions ratio variations

“…In this context, Variable compression ratio engines (VCR) make a contribution, in which the very last function of the Top dead center TDC piston is adjusted to optimize the compression ratio to increase thermodynamic performance, particularly at part load, and finally reduce gasoline consumption and CO2 emissions. Several VCR configurations presently exist [1][2][3][4][5], such as the gear-based crank mechanism engine (GBCM) with variable compression ratio (VCR_MCE-5) [6][7][8][9].…”