Flow calculation in a loop-scavenged direct-injection two-stroke engine

A multidimensional calculation method is used to investigate the flow in a loop-scavenge direct-injection two-stroke engine. The flow is of two phases: liquid fuel is directly injected into the gas field within the cylinder. The governing equations for the gas phase are formulated in the Lagrangian-Eulerian form such that the computational grid lines can move in accordance with the piston motion. The discrete droplet model is used to simulate the liquid phase. In this model each computational droplet represents a number of droplets possessing the same size, velocity and temperature, etc. The dynamics of the droplets is described by the Lagrangian conservation equations. The solution method used is based on the EPISO algorithm. Results show good agreement with measurements in predicting spray penetration for a non-evaporating and an evaporating spray. As for the engine flow, numerical simulation indicates that a tumbling vortex is formed in the cylinder after the ports are closed. This vortex is the most distinguished flow pattern and persists into the late compression period. The gas flow has determinant effects on dispersion of the droplets. The penetration of the fuel spray is obstructed by the scavenging flow during the injection period and the droplets are then transported by the gas flow. It is also shown in the results that the droplet distribution and thus the evaporation rate are affected by changing the injection orientation.