Research On Dynamic Characteristics And Structural Optimization Of Vehicle Dual-stage CNG Pressure Reducing Valve

With the continuous grow of national car parc,urban air pollution caused by car exhaust emission has become a urgent issue of public concern in China.As an engine alternative,natural gas drew people’s attention was due to the high combustion efficiency and calorific value on the one hand and the less emission of pollutants compared to traditional gasoline and diesel on the other hand.It is simple and cost-effective to refit a gasoline engine into a gasoline/CNG dual-fuel engine,so it is widely used in urban vehicles.As an important component in CNG automobile fuel supply system,pressure reducing valve(PRV)plays an important role in decompression and regulation of natural gas supply.This kind of performance has a profound effect on whether the natural gas injector can accurately supply natural gas according to various engine operating conditions..The main research contents and achievements of this study are as follows:1.Current research status and development course of CNG automobiles was summarized.The research status of structural parameters and internal flow of PRV was introduced.Then research background and importance of this study were given out.Finally the main research content was proposed.2.Taking a certain type of vehicle dual-stage CNG PRV as study objects,a method to study the static and dynamic characteristics of the valve was proposed based on its working principle.Combining with the research results of domestic and foreign scholars,the main characteristics of the PRV studied in this paper are derived by summarizing the features of operating conditions.3.Mathematical models of a certain type of vehicle dual-stage CNG PRV and the injector in the supply system was derived.The comprehensive static characteristic equation of this PRV was deduced as the basis for simulation analysis.Then,the relationship equation between the flow rate and the structural parameters of the PRV was established to provide a theoretical basis for structural parameters optimization.4.The simulation models were built up in AMESim,two chambers of the PRV are connected nonlinearly to improve the accuracy of the simulation models.As a result,the dynamic and static characteristic curve of the PRV were described.Then,influence of those structural parameters on its dynamic characteristics were studied and the optimal value of each parameter was determined after comparative analysis.5.A performance-testing bench for this vehicle dual-stage CNG PRV was built up.The tests show that the improved PRV has improved the stability of the flow characteristics by 25%under small flow conditions and the stability of the pressure characteristics by 80%.The stability of the flow characteristics is improved by 50%under large flow conditions.The stability of pressure characteristics increased by 77.8%,which achieved the effect of structural optimization.