A Research Of Inlet Structure Effects On Gas Flow For Big Bore Natural Gas Engine

Development and application of the gas engine can effectively promote the restructuring of energy and emission reduction in China. Increasing power density, improving the thermal efficiency and reducing emissions are the research hot spots on natural gas engine development. Reasonable airflow for natural gas engines to achieve clean and efficient combustion has a significant impact, while the inlet structure is a key factor to decide the cylinder air volume and swirl strength, directly impact on airflow and combustion processes. The inlet gas nozzle and throttle are arranged in the gas engines, the structures of which also affect the gas flow in the cylinder. Therefore, the tandem tangential inlet of a medium-speed big bore natural gas engine is used for the research, and the influence of the structure of inlet, the gas nozzle and the throttle on gas flow in the cylinder is studied by using CFD simulation method and inlet steady flow test method. Specific studies are as follows:First, by applying the CFD simulation study, the main characteristic parameters of the natural gas engine inlet structures are proposed: the inlet orientation angle Av, the inlet throat diameter dv, the valve sealing cone angle An and the bending radius R, and their influence of gas flow are studied. The simulation results show that: when Av decreases 7%,the inlet average flow coefficient is reduced by about 2%, with the increase of about 25% of the average swirl ratio; when dv decreases 4%, the inlet average flow coefficient is reduced by about 3%, with the increase of about 10% of the average swirl ratio; when An decreases 17%, the inlet average flow coefficient is reduced by about 2% with the decrease of about 15% of the average swirl ratio; when R decreases 7%, the inlet average flow coefficient is reduced by about 0.2%, with the increase of about 2% of the average swirl ratio. While the influence of each of the main characteristic parameters on gas flow can be used in the design and development of the inlet on the similar engines, if considering to increase the liquidity of inlet, throat diameter dv should be increased preferentially; if considering to increase the swirl strength of the inlet, the inlet orientation angle Av should be increased preferentially.Then, by applying the CFD simulation study, the influences of the structure on the gas nozzle and the throttle on gas flow are determined. The simulation results show that: After the installation of gas nozzle and throttle the inlet performance is slightly worse, with the decrease of about 4% of the average flow coefficient and the decrease of about 2 % of the average swirl ratio. in fact, this affects mainly are from the gas nozzle structure.Finally, the test pieces are processed by applying 3D printing rapid prototyping technology, and the method has the characteristics of high accuracy and short processing cycle, greatly reducing the impact of casting deviation on the test results, and greatly shortening the processing cycle. At the same time the inlet steady flow test verifies the accuracy of the CFD simulation. The analysis shows that: the steady flow simulation and experimental results have a high consistency; the deviation of the average flow coefficient is controlled within 3%, and the deviation of the average swirl ratio is controlled within 10%.Research on this topic achieves qualitative judgment and quantitative analysis of the inlet performance by using CFD simulation technology. Combining CFD simulation technology and inlet steady flow test can be used as an important means of design and development of the inlet.