| Sequential turbocharging (STC) system is a turbocharging system that can solve the problems of difficultly taking account of high and low conditions for high power density engine. High efficiency in different conditions can be maintained by switching different turbochargers, at the same time, STC system has a relatively simple structure, and it is controlled easily. In this paper, performance improvement calculation for 150 diesel engine is conducted, and calculation schemes of multi-phase STC system and two-phase STC system with single sequential turbocharger(SST)s are emphatically carried out. The scheme of optimal STC system is determined by analysis on results of steady and transient state. The main contents include:(1) Simulation model of original 150 turbocharging diesel engine is established, and it is checked according to test results. Matching calculation is conducted subsequently according to improved requirement for BMEP, performance of improved engine is analyzed.(2) Study on schemes of two-phase and three-phase STC systems of 150 diesel engine is carried out, two-phase STC system with two equal size and two unequal size turbochargers and three-phase STC system with three equal size turbochargers are included. Performance simulation and analysis are carried out for each scheme, study on switching speed is conducted to target the fuel economy.(3) Study on scheme of STC system with SSTs is conducted, principle of SST is analyzed, influence of mass flow multiplier in compressor model for STC system is researched, switching scheme of two-phase STC system with two SSTs is obtained by calculation analysis for whole conditions.(4)Calculation and analysis for engine transient performance of switching process of different STC systems are carried out, fluctuation of engine speed and response time of turbocharging system in the process of switching valve are compared to determine the STC system with optimal transient switching process.Three-phase STC system is optimal in second condition is indicated by economy analysis on the steady conditions among STC schemes. Compared to common turbocharging system, the maximum reduction of specific fuel consumption is 29.8 g/kW·h below 1900 r/min,two-phase STC system with SSTs is optimal in first condition, the maximum reduction of specific fuel consumption is 28.5 g/kW·h below 1500r/min compared to common turbocharging system. By calculation study on transient condition, it can be seen that three-phase STC and two-phase STC systems with unequal size turbochargers have higher switching speed and better transient response in result of smaller change of flow area in switching process. |
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