Simulation On Micro-pilot Injection Strategy Of Marine Medium-speed Dual Fuel Engine

Micro-pilot diesel igniting natural gas dual fuel engine has a excellent performance on emissions and fuel consumption,therefor catches widely attention,especially in the field of marine medium-speed engine,predicting a broad market prospect.As the injection strategy of pilot diesel under different conditions influences the engine performance directly,and carrying out experimental study takes a long test cycle and a high cost with high risk,using modern computer and simulation technology to study the injection strategy of pilot diesel in engine prototype development helps shorten the development cycle and reduces the cost of debugging.The dissertation takes the ACD320 DF,a micro-pilot diesel igniting natural gas marine medium-speed dual fuel engine as the research object,aiming at optimizing the injection strategy of pilot diesel.By taking the multi-dimensional engine model and obtaining the boundary conditions,the dissertation studied the mixture formation in cylinder,the spray field in cylinder,the flow in cylinder and the combustion process in cylinder,analysed how the injection strategy of pilot diesel affecting the performance of dual fuel engine,and eventually optimized the injection strategy of pilot diesel.The dissertation's researching contents are as followed:(1)A quasi-dimensional model of ACD320 DF was built using the software of AVL BOOST.Caculation of dual fuel in gas mode at the loads of 25%,35%,50%,75%,100% in terms of propulsive characterastics was conducted,after which the results was compared to a third party.The quasi-dimensional simulation provided the multi-dimensional simulation with several series of boundary conditions,such as inlet and exhaust temperature and pressure,the initial in-cylinder temperature and pressure,the injection rate of natural gas and so on.(2)Multi-dimensional model of the prototype engine was built according to the geometry data,initial conditions and boundary conditions provided by quasidimensional simulation.Analysis was conducted at the loads of 25%,35%,50%,75%,100% in terms of propulsive characterastics to figure out how the injection quantity of pilot diesel and the injection timing influences the combustion process of the engine,and further analysis of the injection parameters' regular effects on the economy and emission behavior was performed,in which the conflicting relationship of economy and emission was also analysed quantitatively.(3)On the basis of verifying the regular effects of micro-pilot diesel injection parameters and meeting the standard of certain economy and emission,injection timing and quantity under different loads were optimized successively.After the optimum injection time was determined,the optimum injection time was set as the midpoint and then a injection timing range was studied out also.Finally the optimum injection timing and quantiy parameters under different loads were figured out.The dissertation did a pre-research job on micro injection parameters coupled with the development process of the marine medium-speed engine with independent intellectual property of China by means of simulation,and provided technical reference for the integrated control strategy of marine medium-speed engine and its followed bench test.