Analysis of efficiency of a blowdown-exhaust system of a two-stroke diesel engine at use of the adjustable nozzle apparatus of a turbocharger

Abstract

The paper investigates the defining characteristics of the purge-exhaust path of a marine two-stroke diesel engine for a wide range of changes in external operating conditions and loads of the standard variant and the variant with controlled rotating blades of the turbine nozzle apparatus of the turbocharger turbine. The analysis of flow characteristics showed an increase in air and gas flow rates with a decrease in the effective cross-sectional area of the turbine when the blades are rotated. The efficiency of the purge-exhaust path was assessed by the indicators determining the quality of cylinder cleaning from residual combustion products. The following indicators were taken as such: residual gas ratio, filling ratio, total excess air ratio. For the standard variant, the transition to the weighted screw characteristic leads to a decrease in the residual gas coefficient. In the variant with adjustable nozzle this coefficient increases, which can increase the intensity of deposits of carbon deposits on the inner surfaces of the cylinder-piston group. Weighting of the screw characteristic did not lead to deterioration of the cylinder filling with air charge. The use of adjustable nozzle apparatus allowed to increase the total excess air ratio at the modes of fractional loads, the increase of which with the weighting of the screw characteristic increased.