| With the birth of new energy exploration technology and the discovery of clean new energy,the prospect of gas energy market is promising.In recent years,as a new type of energy source,gas fuel engine has been widely concerned.The structure design of the intake system largely determines the quality of the air flow organization and the degree of combustion.At the same time,for the electronically controlled fuel injection device which is arranged in the intake manifold,its outflow structure,injection law and control strategy of high pressure injection play an important role in controlling the Engine air fuel ratio,also have an important impact on the flow field in cylinder.Therefore,using the intake system of a high power gas engine as the research object,the inlet flow field distribution is analyzed and the inlet structure is optimized;The flow structure of the electronic controlled injection device is optimized and the static and dynamic jet characteristics are studied combined with experimental verification;By means of computational fluid dynamics and bench test,the effects of different injection strategies on the mixing characteristics of the cylinder were studied.While improving the efficiency of the inlet and the mixing uniformity of the cylinder,it lays the foundation for the development of the real time control strategy of air-fuel ratio.Specific work and research contents are as follows:(1)The inlet structure was analyzed and optimized by CFD,and the pressure field,velocity field and turbulent flow field in the single cylinder steady state process of the high power gas engine are simulated,and studied the influence of the geometric structure of the airway on the flow field under different valve lift,the two main parameters of the flow loss in the airway such as the fillet of the airway and the arc of the valve cone were optimized,compared with the original airway,the mass flow rate,volume flow rate and turbulent kinetic energy of the working fluid in the cylinder were improved.With the optimization of these two parameters,the mass flow rate and volume flow rate of the mixed optimization were increased respectively by 6.67% and 6.69%,and the turbulent kinetic energy of the unit working fluid was increased by up to 44.9%,the performance of the circulation of the gas and the mixture of working fluid were enhanced.(2)Flow characteristics of injection device is analyzed by means of the combination of computational fluid dynamics and bench test,and the ejector structure is optimized,the flow rate of the optimized spray device is about 2.97%,which improved the injection efficiency and the mass flow rate is increased when the pressure difference is 0.4MPa.The static and dynamic jet characteristics of the injector are analyzed,by comparing the simulation results with the experimental results,it is found that the relative error of volume flow is not more than 5%,and the relative error of mass flow is controlled within 4%,which proves the validity of the simulation results,using the cftool toolbox in MATLAB to fit the mapping relationship between the mass flow qm and the valve lift h and the inlet pressure difference p,the fitting error is less than 3.5%,the mapping relation is reliable.(3)The mixing characteristics of engine cylinder under different injection strategies were studied.The effects of different angle of the intake lag angle,the composition of the fuel and the injection strategies,installation position of the injector on the mass fraction of methane in the intake port and the cylinder were analyzed.That spray the starting point for the 340oCA is better than starting point of 350 oCA when it comes to the intake adequacy of In-cylinder mixture.The injection pulse width,injection pressure and methane content of gaseous fuels are inversely proportional to the air-fuel ratio,when the injection pulse width is 78oCA,cylinder air-fuel ratio is 17.5,close to the target air-fuel ratio.Test verified that open / closed t transition time of injection valve were less than 3.5ms,which meet the technical requirements;Compared with the original engine,the improvement effect of the cylinder uniformity of the high power gas fuel engine with electronic controlled injection device is about 10%?... |
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