Dynamic Design of Crank-Rocker SI Engine Mechanism

Purpose In this study, a single-cylinder engine using a crank-rocker mechanism has been kinematically examined for two distinct cylinder volumes (402 cc and 1140 cc) which are sufficient to generate the power required by automobiles. Methods Variations of in-cylinder pressure have been formulated based on experimental data. A compulsory expression for the determination of internal pressure change with real time has been obtained with the help of Dirac delta function and the obtained results have been favorably compared to measurements. Such significant kinetic parameters, including inertia torque, gas torque, indicated power and crank power generated on a crankshaft, have been first computed for the crank-rocker as well as the slider-crank mechanism and then compared to each other. Results From the comparisons between crank-rocker and slider-crank, it has been deduced that the crank-rocker mechanism leads to higher bearing forces. Moreover, inertia effects and gas torque increase with spark time in both mechanisms. Furthermore, the crank-rocker mechanism causes different velocity zones on the piston surface. Additionally, the crank-rocker mechanism allows the dimensions of its moving links to be reduced without change in the gas torque by considering an optimum transmission angle. Finally, although there is good agreement in the kinematic values, it has been shown that the theoretical power is different from the indicated power in the literature. Conclusions It was shown that the proposed crank-rocker mechanism offers many advantages over the conventional mechanism with slider-crank when they are examined dynamically.