Research on Characteristic of Variable Exhaust Valve Timing of Marine Large Power Slow-speed Intelligent Diesel Engine
|School||Wuhan University of Technology|
|Keywords||Intelligent marine diesel engine Variable exhaust valve timing Hardwarein loop|
Increasingly stringent environmental regulations made a technical request to improve the performance of a marine diesel engine.Marine low-speed diesel engine uses intellegent techno logues which include high pressure common-rail fuel injection electrically controlled and flexsible exhaust valves electrically controlled to reduce emissions of harmful gases.The Intelligent technologue has become the development direction of the marine diesel engine.The intellegent diesel engine implements the flexiable electical control of the variable exhaust timing by Electronic-Hydraulic driving, which optimizes the performance of the diesel engine at all loads. Because of the blockade of the core technologies of the marine intelligent diesel engine by foreign companies, such as the flexiable electical control of the variable timing of the exhaust valves, the research on the variable exhaust timing of the exhaust valves for the intelligent marine diesel engine should be carried out. So it is great significant to master the core technilogues and to improve the overall technological levels of the domestic marine diesel engine industry.The key issues for the low-speed intelligent marine diesel is focused on, the Wartsila5RT-flex60C marine diesel engine is set as a research objective, a HIL (hardware In loop) benchwork for the large power intelligent marine diesel is developed.The characteristics of the variable exhaust valve timing on the intelligent marine diesel engine are investigated. A simulation model of the diesel engine working process is built, the effect on the performance of the diesel engine by the variable exhaust valve timing is analysed. The technical foundation for designing the princple of the control strategies of the variable exhaust valve timing is laid. The research content and the main research results in the following aspects:The techinical characteristics of the low-speed intelligent marine diesel engine were summarised. The hardware component, the software structure and the control principle of the intelligent system were analysed. The realtime simulation model of the diesel engine based on "cylinder moving" was built. Multi-function HIL simulation workbench for the intelligent system of the marine diesel engine based on Lab VIEW software platform and cRIO (compact reconfigurable I/O) controller was developed. The funcions andthe accuracies of the HIL simulation workbench were validated by tests. The HIL tests of the variable exhaust timing of the inteligent system were implemented, which provided the conditions for researching on the variable exhaust valve timing of the intelligent system.The HIL simulation tests of the variable exhaust valve timing was carried out on the Multi-function HIL simulation workbench for the intelligent system of the marine diesel engine. The characteristics and rule of the variable exhaust valve timing were presented. WECS (Wartsila Electrical Control System, WECS) uses close-loop control method. The threshold for opening exhaust valve is15%of opening full stroke and the threshold for closing exhaust valve is85%of closing full stroke.The exhaust valve timing (the opening angle, the closing angle and the delay angle) variants with the changes of the loads of the diesel engine. WECS advances the duty cycle of PWM (Pulse Width Modulation, PWM), enlarges the opening of the servo oil pump and increases the pressure of the rail. The lift of exhaust is effected by the variant of the rail pressure.The exhaust opening delay time decreases when load of the diesel engine increases and the rail pressure increases. The speed of the diesel engine advances by the increasing of the diesel engine’load, then the exhaust delay angles advances. The exhaust valves are closed by the force of the air spring and the delay time of closing changes few when load increases. The speed of the diesel engine increases then the exhaust valves closing delay angles advances.The simulation model for working process of RT-Flex60C intelligent diesel engine was built. The Simulation model was validated by test data both of Multi-function HIL simulation workbench for intelligent system and of workbench of the marine diesel engine. The analyzing of the test results are shown below. The marine diesel engine with the variable exhaust valve timing is able to conform NOX Emission standards of IMO Tier Ⅱ. When the inlet pressure and the fuel system parameters, such as a fuel injection quantity, a fuel injection start angle, a injection duration and other conditions, remain unchanged and exhaust valves, the opening angle delays of the exhuanst valves, Specific Fuel Consumption (ge) decreases and the reduction of exhaust opening duration leads to the increase in total cylinder gas, the abatement of exhaust gas and the tempeture of the cylinder gas and the advances of NOX emission. The increase of total cylinder gas leads to the increase of cylinder gas compression terminal pressure and break pressure. When the exhaust closing angle delays, the total cylinder gas decreases, the cylinder gas compression terminal pressure and break pressure reduce, cylinder combustion temperature increases and NOX Emission advances. The decrease of cylinder gas pressure leads to the reduce of effective power, and Specific Fuel Consumption (ge) decreases advances when fuel injection quantity dosen’t change. The variable exhaust timing control strategy should first meet the diesel engine mechanical load and emissions regulations, and then optimize the fuel consumption rate of the target.