Design Of Control Flap For Sequential Turbocharing System Of Diesel Engine And Integration

Sequential turbocharing technology is one of the effective measures to improve the internal combustion engine performance under low load. The control valve for sequential turbocharging system is a key component to ensure a smooth transition between turbocharging operating modes, and its performance will directly determine the effectiveness of the sequential turbocharging system. Generally, the control flap used in the domestic sequential turbocharging system is wafer double eccentric butterfly valve, which is not individually designed. As a result, the size of system will be large, and its structure is not compact. Therefore, it is necessary to design a special flap for sequential turbocharging system in consideration of integration among control valve?turbochargers?intake and exhaust lines. Thus, the optimal system with optimal structure and minimum size can be obtained.In this paper, a set of gas control valve is designed for TBD234V12 marine diesel engine,which is a double eccentric metal seal butterfly valve with a special link mechanism actuator driven by a double-acting cylinder, As a consequence, the control valve is downsized and its weight is reduced comparing with industrially valve.Three-dimensional flow simulation of the designed gas flap is completed using CFD software, and a analysis of the influence of the disc as the flap is been open is carried out. The results showed that when the valve opening angle is small, apparent turbulence occurs near the flap disc, while with the opening angle increasing, the vortex motion decreases, and the gas flow is relatively stable near the flap disc. To explore the influence of valve opening speed to the flow after valve, transient simulation is also calculated. The results show that the butterfly valve responds slowly, as the gas flows smoothly after the disc, and vice versa.1D transit simulation code is made to study the influence of the valve response time of opening and closing to transition process based on TBD234V12 diesel engine. The simulation result shows that in the process of controlled turbocharger putting into operation, shorter the gas valve response time is and longer the air valve response time is, the higher the engine speed fluctuations is. Through comparison and analysis, the reasonable control valve open response time is: 1.2s for gas valve and 0.2s for air valve.Experiments is done to study the switching process of diesel engine by adjusting the air pressure of actuator in order to control the valve response time of opening and closing.Experiment results show that in the process of transition from 1TC mode to 2TC mode, the diesel engine could switch smoothly if the gas control flap open slowly and the air control flap open fastly, and the reasonable valve response time is 1.01s for gas control flap and 0.25s for air control flap. The result also demonstrate 1D simulation model is correct.