Optimization Research On Parameters Match Of Double-Layers Diffluent Combustion System For DI Diesel Engine

Based on the concept of space-atomization and spray-impingement, in order to optimize the new Double-Layers Diffluent Combustion System of DI Diesel Engine, considering the quality of mixture in the cylinder, the ratio of air utilization, the combustion efficiency and the emissions performance of the combustion system, several factors have been adjusted,such as the injection pressure, injection timing and the matching between the spray and the structure of the chamber chamber in this dissertation, so that the fuel can impact on the spray-oriented stairs effectively and then expand into two parts along the oriented-surface. Thereby the combustion process in the cylinder and the engine performance can be improved.Finally the purpose of the optimization of the new combustion system can be realized. A series of CFD simulation and experimental research were carried out,the specific works are as follows:(1) In order to achieve the goal of the optimization for the new Double-Layers Diffluent Combustion System, three different combustion systems with different structures and dimensions were designed, considering the relative researches before and the factors that can determine the performance of the system. The principle of design and the method to determining the structural parameters were introduced in detail.(2) Three-dimensional geometric mode and numerical simulation about the formation process of mixture, the flow of the mixture, the distribution of fuel and gas equivalent ratio and the combustion processes in the three different Double-Layers Diffluent Combustion System were carried out with AVL FIRE2008.The matching between the cylinder structure and the position of the fuel injection, the control strategies for the injection timing were also studied. The analysis showed that:among the different combination of a variety of hardware, software and control strategies, the combustion chamber Ⅱ with the condition of the extend nozzle height1.4mm and injection timing of9°CA BTDC was the best option.(3) The experiments for the three different Double-Layers Diffluent Combustion Systems were conducted on a single-cylinder135diesel engine. The influence of injection pressure, the number of nozzle holes, the position of injectors and injection timing on the performance of the three systems were tested on this engine.The advantages and disadvantages of different design methods were analyzed based on the experimental data.(4) A comprehensive analysis of numerical simulation and the whole experiment results shows that:the quality of the matching between the position of the spray-oriented stairs with a variety of conditions and perimeters in new combustion system has a direct impact on angel, distance and position of spray-impingement. Considering economic and emissions performance of the engine, analysis for optimization shows that with the condition that the injection pressure is110MPa, the number of injector nozzle hole is8, protruding height is1.4mm, the injection timing is9°CA BTDC, structure Ⅱ of the combustion chamber has the best performance compared to the other matching methods. At this condition, type Ⅱ has the most effective utilization of the ubiquitous diesel spray impingement, the spatial distribution and the atomization of the spray are improved, also a rapid homogeneous mixture and combustion of the air and fuel is promoted.