Simulation Study On Gas Supply System Of Gas-fueled Engine

Natural gas has the characteristics of compressibility,high density influenced by pressure and temperature,which poses a challenge to the multi-point injection gas supply system of gas fuel engine.The gas supply system is required to supply gas to each cylinder of the engine on a regular and quantitative basis.The multi-point injection gas supply system of natural gas engine directly affects the fuel economy,power performance and emission performance of the engine.The research on multi-point injection gas supply system of natural gas engine can,on the one hand,optimize the attenuation of pre-valve pressure in the process of injection of gas injection valve,increase the amount of gas injection valve,and reduce the inconsistencies in the process of valve injection.Thus reducing the engine cylinder working inconsistencies.In this paper,a one-dimensional and three-dimensional coupling simulation modeling method is presented.The variation of total pressure in front of the valve,the amount of gas injection and the pressure fluctuation characteristics in the air rail under different working conditions of the engine are studied,and an improved optimization scheme is put forward.In this paper,the one-dimensional modeling method is used to obtain a preliminary gas injection valve model,and the trend of gas injection valve law is predicted.Because one-dimensional modeling is difficult to provide accurate dynamic boundary conditions,there are some limitations.Then,according to its limitations,one-dimensional three-dimensional joint simulation modeling is carried out,and the joint simulation calculation under multiple injection pressures and multiple injection pulse widths is carried out.The calculated results are in good agreement with the experimental results.Among them,the maximum error between the calculated results and the experimental results is less than 6%.In this way,the accurate gas injection valve model is obtained.After the above-mentioned accurate model of gas injection valve is obtained,based on the practical experimental platform,an equivalent one-dimensional and three-dimensional joint simulation model of multi-point injection gas pipeline system for gas-fueled engine is established.The pipeline model and valve model are Flowmaster one-dimensional model,and the engine air-rail model is Fluent three-dimensional model.The two models realize real-time bi-directional data transfer and coupling with the interface software-MPCCI,developed by the Institute of Scientific Computing and Computing methods of Fraunhofer in Germany.In this way,the integration of "macro" and "micro" angles can be realized by taking into account the dynamic characteristics of the system as well as the detailed flow mechanism in the components.The calculated results of the model are in good agreement with the experimental results.Then,based on the above-mentioned model of engine gas pipeline system dynamic characteristics of the settlement results,at the same time,combined with the gas-rail flow field analysis,It is concluded that the reasons for the deviation of the gas injection from the normal value and the excessive attenuation of the pressure before the valve are due to the excessive pressure fluctuation in the gas rail and the strong flow separation between the branch and the body of the gas rail.According to the above two points,the optimization and improvement method is put forward,which is to increase the air rail body diameter and set the transition fillet in the air rail body and the air rail branch,and to study the different body diameter and the different transition fillet diameter under the condition of different body diameter and different transition fillet diameter.According to the law of pressure change in front of gas injection valve,the optimum parameters of gas rail and upstream pipeline are determined,and the optimization of engine gas pipeline system is completed.