In-Cylinder Air-Flow Characteristics Using Tomographic PIV at Different Engine Speeds, Intake Air Temperatures and Intake Valve Deactivation in a Single Cylinder Optical Research Engine

摘要

Fuel-air mixing is the main parameter, which affects formation of NOx and PM during CI combustion. Hence better understanding of air-flow characteristics inside the combustion chamber of a diesel engine became very important. In this study, in-cylinder air-flow characteristics of four-valve diesel engine were investigated using time-resolved high-speed tomographic Particle Imaging Velocimetry (PIV). For visualization of air-flow pattern, fine graphite particles were used for flow seeding. To investigate the effect of different operating parameters, experiments were performed at different engine speeds (1200 rpm and 1500 rpm), intake air temperatures (room temperature and 50°C) and intake port configurations (swirl port, tangential port and combined port). Intake air temperature was controlled by a closed loop temperature controller and intake ports were deactivated by using a customized aluminum gasket. Imaging was done by two CCD cameras and timing synchronization was done using external clock pulse synchronizer. Two directional projections of captured flow-field were pre-processed to reconstruct the 3D flow-field by using the MART (multiplicative algebraic reconstruction technique) algorithm. Ensemble average flow pattern was used to investigate the air-flow behavior inside the combustion chamber during the intake and compression strokes of an engine cycle. In-cylinder flow visualization indicated that energy dissipation was the maximum near the end of intake stroke. The non-homogeneous and highly fluctuating flow of intake stroke became uniform during compression stroke. In-cylinder air-flow characteristics were significantly affected by engine speed. Air velocity and turbulence was found to be significantly higher at higher engine speeds. Tangential port configuration showed highest rate of energy dissipation, which resulted in minimum absolute air velocity. Comparison of all operating conditions showed that 50°C and swirl port open configuration provided superior in-cylinder flow condition for better fuel-air mixing, resulting in improved combustion, emissions and performance.