Shape Parameterization and Optimization of a Two-Stroke Engine

Abstract

We demonstrate a procedure for designing and optimizing the scavenging properties of a two-stroke engine. A method of surface design, known as the partial differential equation method, is used to represent the internal geometryoftheengine.Wethenrunsteady-statecomputationale uiddynamicscalculationstoassessthescavenging e ow inside the engine. To quantify the scavenging, the trapping efe ciency is used, and calculated values of this measure are obtained for different geometrical designs. We use a locally weighted regression-smoothing model to e t the data, and then we optimize the resulting response surface. The optimization captured two local minima, one of which corresponds to accepted manufacturing practice and the other one is a new and counter-intuitive way of scavenging the engine, having optimum scavenging characteristics. Nomenclature C = contour M = mass of air n = number of particles r0 = bore of the cylinder u, v = surface parametric coordinates V = volume of air X = vector of Cartesian coordinates of surface points Xn = normal derivative along the boundary x, y, z = Cartesian coordinates xsu = derivative parameter of the transfer port, in x direction, on C0 ysl = derivative parameter of the transfer port, in y direction, on C1 ysu = derivative parameter of the transfer port, in y direction, on C0 zsu = derivative parameter of the transfer port, in z direction, on C0 a = smoothing parameter q = density Subscripts s = supplied t = trapped 0, 1 = upper and lower surface boundaries, respectively