| The marine diesel engine is the heart of a marine power system,which accounts for more than 95% of the market.Increasingly stringent emission regulations present severe challenges to the emission performance and the life cycle of marine diesel engines in service.The "Limits and Measurement Methods for exhaust pollutants from marine engines(China I and II)"(GB15097-2016)promulgated by the Chinese government will be in effect on July 1st,2021.The marine engine of inland watercraft has a high proportion of low-load operating conditions.Moreover,the mechanical fuel system cannot adapt to the operating condition changes,resulting in poor emission performance and fuel economy at non-design points.In response to the above-mentioned problems,the modification,the upgrade and matching technology of in-service medium-speed diesel engine fuel system were studied in the thesis.Without changing the combustion chamber and the inlet/outlet system of the baseline engine,the mechanical fuel injection system was retrofitted with a high-pressure common-rail(HPCR)system.A flexible control of high-pressure fuel injection could be achieved under all operating conditions.By optimizing diesel engine performance,NOx emissions could reach IMO Tier II standards or China’s Phase I standards,while reducing fuel consumption under all the operating conditions.The research has certain theoretical significance and engineering application value.The main contents and conclusions are as follows:The design and technical requirements of the high-pressure common-rail system retrofitting for the target marine medium-speed diesel engine were analyzed.The key components such as fuel injectors and high-pressure fuel pumps were integrated and optimized.A series of tests had been conducted on the HPCR performance test platform,including high-pressure sealing and leakage,functional integrity,hydraulic fluctuation characteristics and fuel injection characteristics,etc.The mechanism and influencing factors of the pressure wave in the high-pressure circuit were analyzed.The influence of common rail structure on the consistency of fuel injection was analyzed by tests.The DOE method was utilized to optimize the hydraulic-network layout of the HPCR system.The experiments of rail orders and injection sequences were carried out to study the influence of different hydraulic layouts on the energy distribution of pressure waves in the common rail system.A comprehensive and detailed model of the HPCR system was established and verified.The influencing factors of the hydraulic characteristics and fuel injection characteristics of the HPCR system were analyzed by the combination of Monte Carlo random and MOGA-II algorithms.The key structural parameters and optimal designs that affect the main performance indicators of the HPCR system were figured out.The 3D simulation model of the original engine was established and verified to investigate the effect of high-pressure fuel injection on the in-cylinder mixture formation and combustion process.The influence of the interaction between the high-pressure fuel spray and the chamber on the combustion process and the emission was studied.Then,the performance of the HPCR marine diesel engine was predicted and analyzed under different operating conditions to figure out the effects of different injection parameters on the combustion process,mechanical load,thermal load,fuel economy and emissions performance.Moreover,the multi-objective optimization algorithm was applied to study the injection timing,duration and mass,which provided a theoretical basis and data support for the development of injection control strategies.Through the integration of the HPCR system,the virtual engine and the electronic control system,the hardware-in-the-loop(Hi L)simulation platform for the marine medium-speed diesel engine was established.A real-time engine model that can simulate the high-pressure fuel injection process was linked to the fuel system actuators through the common-rail pressure signal,injection rate and injection delay data.Base on the Hi L platform,the functions and reliability of the control system were verified.Additionally,the fuel injection control strategy of the HPCR system was virtual calibrated and optimized.On the test bench of the marine medium-speed engine,the mechanical fuel system has been retrofitted with the HPCR system.The matching test between the HPCR system and the diesel engine was carried out,and the fuel consumption and the emissions performance were optimized under all operating conditions.The NOx emission meets the IMO Tier II limits and the maximum reduction in fuel consumption rate reaches 11.15% simultaneously.After further optimization of the injection parameters,the NOx emissions were further reduced to meet the requirements of China I(GB15097-2016),and the fuel consumption was declined by7.65%. |
PDF Full Text Request