Effect of Inlet and Exhaust Pressures on the Scavenging Characteristics of a Carbureted Uniflow Scavenged Engine

The effect of inlet and exhaust manifold pressures on the scavenging and fluid flow inside a turbocharged, carbureted, uniflow scavenged two-stroke engine has been studied numerically. An axisymmetric computational code, CARE, has been used for the purpose. The inlet pressure is varied between 0.25 MPa and 0.29 MPa, keeping exhaust pressure constant at 0.23904 MPa, to study the effect of inlet pressure. Similarly, the exhaust pressure is varied between 0.2 MPa and 0.25 MPa, keeping inlet pressure constant at 0.26104 MPa. The results are plotted in the form of velocity vector plots, fresh charge concentration contours and swirl velocity contours to illustrate the flow field at various crank angles. The global quantities, viz., the cylinder pressure, total mass of gases in the cylinder, fresh charge and residual gas masses in the cylinder during scavenging are plotted as functions of crank angle, for various values of the inlet and exhaust pressures. The various gas exchange efficiencies are also plotted as functions of the inlet and exhaust pressures. The results obtained indicate that the inlet-to-exhaust pressure difference governs the mass flow rate across the inlet and the exhaust ports, and the velocity of the gases at the inlet and the exhaust have a strong influence on the flow field and scavenging. The delivery ratio is higher for a larger inlet-to- exhaust pressure difference, giving rise to better scavenging and charging, and inferior trapping.