Airflow in the cylinder of a 2-stroke cycle uniflow scavenging diesel engine during compression stroke

Abstract

The scavenging process of a 2-stroke cycle engine dominates not only fresh-air charging but also the airflow in a cylinder at the compression end. So, the combustion performance of a 2-stroke cycle diesel engine depends on scavenging efficiency ηs, and the scavenging-air swirl intensity in the cylinder. In this report, first, the scavenging airflow is investigated by operating a 2-stroke cycle engine rig. From the LDV measurement of the air velocity in a cylinder during the compression stroke, it is shown that the scavenging port made by the combination of a large-angle port and a small-angle port has high scavenging ability and sufficient swirl intensity for air-fuel mixing. Secondly, the numerical analysis method of the gas flow in a cylinder during the compression stroke is developed. This method employs an approximation of a 2-D axisymmetrical flow to save computation time, but uses, for the initial condition, the calculated results of a 3-D scavenging flow simulation to ensure the accuracy of the starting swirl-flow pattern which is deeply affected by the port arrangement. Some calculated results are compared with the experimental data, and it is concluded that this method can simulate the flow pattern in a cylinder during the compression stroke with good accuracy.