Performance Study Of Squentially Turbocharged System Of Marine Diesel Engine

The sequential turbocharging technology is the most effective method that improves the performance of diesel engine at low condition. The technology can widen the operation range of engine at low condition, and improve the economy performance of engine, and reduce the exhaust pollutants of engine. But the technology needs autocontrol technology. If the switch delay and switch point of turbocharger of sequentially turbocharged engine is incorrectly controlled, especially with respect to transient process of the engine, it will result in some problem such as compressor surge, turbocharger overspeed and high oil consumption rate. Study object of this dissertation was a sequentially turbocharged diesel engine with intake exhaust bypass and high load condition release air. The dissertation focused on the performance of sequential turbocharging system in order to optimize the match between diesel engine and turbocharger and gain the control law of tubocharged system.The primary originalities in this dissertation include some contents as follows. The simulation software of sequential turbocharging diesel engine with intake exhaust bypass and high load condition release air is developed under MATLAB/SIMULINK simulation platform. A model of sequential turbocharging thermodynamic test rig is established. It is gained that the switch delay and volume of inlet pipe have influence on the switch process of turbocharger. A simulation model of sequential turbocharging diesel engine with PID controlled release valve is established. Means that maximum explosion pressure of cylinder is controlled by the regulative release valve is found. Controls parameter of PID is fixed on. PID controller can realize the optimized control of maximum explosion pressure of cylinder. A regulative sequential compound turbocharger system is designed. It can enlarge the operation range of diesel engine. This paper have studied that intake exhaust bypass had influence on the performance of sequential turbocharging diesel engine. How to confirm the region of intake exhaust bypass is answered. A transient model of compressor is established in SIMULINK language. To predict compressor surge and rotating stall, a time delay is used for taking into account the departure of the compressor characteristics for its steady state. The model validity is verified by experiment data The dissertation simulated transient unsteady process of compressor. The compressor surge is detected by the parameters such as flow rate deviation, flow rate swing, relative pressure deviation, and pressure swing and pressure frequency. The results show that pressure frequency can sensitively and truly detect the compressor surge, that the predicted surge line of compressor are in good agreement with experiment surge line. Surge characteristics are affected by moment of inertia and volume of plenum.A sequential turbocharging thermodynamic test rig model is established in order to investigate the transient performance of the sequential turbocharging system. The test rig is composed of two turbochargers, gas valve, air valve, regulating valve and a combustion chamber. The transient switch process from one turbocharger operation to two turbochargers operation is studied. It is analyzed that the switch delay and volume of inlet pipe have influence on the switch process of sequential turbocharging system. The results show that too short switch delay will induce the controlled turbocharger compressor surge, and that too long switch delay will raise the basal turbocharger compressor surge, and that switch delay in the middle time can avoid the compressor surge. Switch delay in the middle time can avoid the compressor surge. The compressor will not flow backwards if the volume of inlet pipe can not too larger and small.A simulation model was designed for the steady state performance of the turbocharger diesel engine based on MATLAB/SIMULINK in order to study the performance of sequential turbocharging system combining with intake exhaust bypass system. Surge limit and intake exhaust bypass of diesel engine are studied by simulation. The region of intake exhaust bypass is analyzed by experimentation results. The results show that borderline of 2TC+CAB and 2TC of the diesel engine is under the surge limit curve of 2TC. If the controlled compressor occur surge, it will raise the surge of basic compressor. It is simulated the steady performance of the diesel engine that operated 1TC state, 2TC state and 2TC+CAB state under screw propeller characteristic operation. Under screw propeller characteristic operation, it is studied that the widen region of intake exhaust bypass affects the performance of sequential turbocharging diesel engine. When the reduced rotation speed of diesel engine is with the range of 0.8143 and 0.8762, opening of intake exhaust bypass valve can increase surge margin, and avoid compressor surge, and reduce the turbine inlet temperature, and enlarge the operation range of diesel engine.Finally, transient simulative model of sequential turbocharging diesel engine are established. The switch process of diesel engine from one turbocharger operation to two turbochargers operation is studied. The studied results show that it can be avoid that operation point of compressor enter into surge region if bypass valve and gas valve are opened at the same time during the switch process. The speedup and speeddown process of diesel engine under screw propeller characteristic operation is studied. The results show that best switch delay of speedup process should be selected short delay. If the switch point of controlled turbocharger is properly lowered, the compressor surge can be avoided. The results of this research have important guiding value and engineering practice meaning to further popularize and apply sequential turbocharging technology. The results have wide application prospect.Release boost air of the diesel engine is used in order to limit maximum explosion pressure of cylinder. PID controller model is designed. Its input signal is maximum explosion pressure. Its output signal is angle of release valve. The process of release boost air of the diesel engine is studied. Control strategy of release valve is obtained. The PID parameters of controller are turned. Use of antiwindup PI control arithmetic realizes the control of release boost air of diesel engine.