Investigation On Anti-surge Technology For Diesel Engine Sequential Turbo Charging System

Sequential turbocharging technology is the most effective way to improve performance for turbocharged diesel engine, particularly at low load. It can expand operation range, improve economic performance and reduce emissions for diesel engine. However, if the switching point and switching delay time is not appropriate, it is easy to cause compressor surge, turbocharger exceed limited speed, combustion become deteriorate and so on. In order to restrain sequential turbocharging system surge phenomenon in switching process, compressor surge active control technology was applied to anti-surge control in sequential turbocharging system, sequential turbocharging anti-surge control system was developed. Experiment results show that surge active control system can inhibit the spread of surge that caused by sequential turbocharging system switching, it offer a new idea to improve the stationarity and safety for sequential turbocharging system. The main contents of this dissertation are as follows:1. Investigation of the turbocharger compressor steady performance. Sequential turbocharging thermal power test bed was designed and constructed according to the requirements of compressor steady performance and sequential turbocharging switching experiment based on turbocharger test rig and sequential turbocharging diesel engine test bed. The test bed used the combustor to replace the high-power diesel engine to study the sequential turbocharging system. It is easy to adjust turbine inlet parameters flexibly, to control working status, to study the overall performance of the sequential turbocharging system. The test bed can work under circulation mode and blow off mode, it can undertake sequential turbocharging test that is composed of three turbochargers in different structure, it also can carry out single turbocharger performance test including steady and dynamic characteristics. This paper make some research about its working principle, overall structure and measurement and control system in detail, the compressor steady performance experiment was carried out based on the test bed, which supplied experiment data for the test bed circulation mode simulation.2. Study on turbocharger compressor surge. The thermal power system simulation model including single turbocharger was established based on Greitzer compression system model. The dynamic characteristics of compressor mass flow and outlet pressure parameters in surging process were analysed to find out parameters or parameters characteristic which can predict oncoming compressor surge. Compressor surging experiment was carried out based on sequential turbocharging test rig, the compressor surge law versus rotational speed and plenum volume was investigated, spectrum analysis and wavelet analysis were applied to validate the surge precursor signal, the quantitative criterion to judge compressor surge was built. Compressor surge active control hardware-in-the-loop-simulation will be carried out based on dSPACE real-time simulation system and LabVIEW measurement system. Fuzzy control algorithm was applied to develop rapid control prototype which make a basis for sequential turbocharging anti-surge control algorithm.3. Investigation to sequential turbocharging system dynamic switching process. Sequential turbocharging thermal power system simulation model was established to study the law of switching process in different switching delay time and different plenum volume. And the relevant experiments were carried out to validate the simulated results. The results show that the large turbocharger as basic turbocharger, the entering delay time have a greater margin; the small one as basic turbocharger, the entering delay time margin is small in unequal size sequential turbocharging system. The sequential turbocharging system exiting experiment show that exhaust valve should be closed before the air valve, ifnot, the controlled compressor would be in deep surge. If the exiting delay time is short, controlled compressor will be in deep surge; if the time is long, the controlled compressor will be in backflow. It is inevitable that the controlled compressor would be in surge state in exiting process due to the turbocharger keep rotate state when air valve was closed, but it can reduce the surge intension to set reasonable exiting delay time. Meanwhile, the volume size of the surge tank has significant influence for dynamic characteristics of the sequential turbocharging system switching process. It should be taken into account the engine exhaust pipeline impact capacity to the booster compressor system dynamic characteristics in turbocharging system design and matching.4. Development of sequential turbocharging surge active control system. The surge active control system used blow-off valve as control actuator, surge controller software and hardware were designed based on STM32F103 micro-processor andμC/OS-Ⅱembedded real-time operating system. Control system acquires turbocharger rotational speed, compressor outlet pressure and compressor mass flow signal, fuzzy control algorithm was designed based on hardware in the loop simulation control prototype. The transplant method ofμC/OS-Ⅱand realization of fuzzy algorithm were introduced in detail. The test results show that the control system can realize the coming surge signal and inhibit the surge spread. It improved the sequential turbocharging system switching stationarity and safety.