An Analysis of the Engine Blowdown Process Using Multidimensional Computations

Abstract

The details of the blowdown period were studied for the EMD-710 diesel engine by using a multidimensional computational code for in-cylinder flows. Computed results are presented describing both global and detailed features of the flow field during the blowdown period. Global features include variations of cylinder pressure, mass, angular momentum, turbulence kinetic energy, and the exhaust mass. A parametric analysis has shown that the percent pressure drop and the percent mass exhausted are almost invariable with the initial cylinder pressure or mass. Details of the mass convection process within the cylinder are investigated through development of the line separating the downward and upward flowing gas regions. The location and speed of propagation of this separation line are also found to be independent of initial cylinder pressure and mass. The results show that the speed of the separation line is about twice the piston speed for an initial period of 15 deg crank angle. Then it starts to decrease and becomes equal to the piston speed at about 26 deg after the exhaust valve opening. Beyond this time the separation line is slower than the piston speed.