As one of the key systems of the marine power plant diesel engine, the turbocharger directly affects whether the diesel engine can continuously and stably provide the power required for the ship. Owing to a number of uncontrollable factors, such as harsh working conditions and complex structures, the turbocharger may have various failures, causing it to lose its intended function. At present, the fault diagnosis of the marine turbocharger has not been paid enough attention yet and in most cases, the method of ‘ex post diagnosis’ is still adopted. When analysing the nonlinear correspondence between the failure symptoms and failure causes, it is difficult for the existing theories to meet the actual diagnostic requirements. This paper introduces the concept of gas-path diagnosis into the condition monitoring for a marine turbocharger for the first time and proposes the flow capacity index which characterizes the flow capacity of the component and the isentropic efficiency index which characterizes the operating efficiency of the component as two dimensionless evaluation indicators for turbocharger health status. Moreover, the nonlinear mapping relationship between these two health parameters and the gas-path measurable parameters of the turbocharger is studied, and a novel performance degradation evaluation method for a turbocharger is established. The proposed method has been tested in three test cases where the degradation of a model turbocharger has been analysed. These case studies have illustrated that the proposed method can accurately isolate the degraded components and further quantify the degradation of the components.
In order to improve the performance of a V-type diesel engine at low and medium speeds, the compound VGT-STC turbocharger system was proposed. First, the compound VGT-STC turbocharger system bench was established, which allowed to switch between the VGT and STC boosting systems. Then, the load characteristic tests with a variable VGT vane opening were conducted at different speeds in the 1TC and the 2TC, respectively. The results showed that the VGT-1TC could provide much more air into the cylinder than the VGT-2TC at 1000 r/min, and the maximum torque was increased by 4000 Nm (80%), and the BSFC decreased by 20.1 g/kWh on average. The matching characteristics are analyzed for three boosting control strategy systems, including the VGT, STC, and the compound VGT-STC. The results show that the VGT system has a steady increase of the maximum torque in both low and medium speeds, while the STC system has a large increase in torque at 1000 r/min and begins to decline when speed is greater than 1200 r/min, and the compound VGT-STC system combines the advantages of the VGT and STC, which can maintain 9000 Nm (83% rated torque at 1800 rpm) and a lower BSFC at both low and medium speeds. As a result, with the compound VGT-STC boosting control strategy system, the operating range has expanded by 10%, and its smoke opacity, BSFC, and exhaust temperature are reduced by 0.057, 8.2 g/kWh, and 64 °C, respectively.
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