Design And Numerical Simulation Of Porous Media Burner For Ammonia

In order to meet the needs of chemical energy storage,NH₃ has attracted much attention as a substitute for H₂.As an alternative fuel,NH₃ has the following advantages:carbon-free combustion,synthesis from renewable resources,convenient storage and transportation,etc.For the combustion and utilization of ammonia,a very important problem is the emission of NO.As a new combustion mode,porous media premixed combustion can enhance combustion stability and increase the combustibility limit of the burner.Research on the combustion performance of porous media can provide guidance for the design and optimization of porous media burners.The combustion characteristics of porous media for ammonia and NO_xemission were studied by numerical simulation.In this research,a 2D numerical model of porous medium burner is carried out,and the simulation software Fluent is used to simulate the premixed combustion of ammonia fuel.First,a detailed chemical reaction mechanism is used to carry out a numerical simulation study on the combustion process of ammonia/air fuel at an equivalent ratio of 0.9 to 1.2.In order to verify the model,compare the calculated results with the experimental results in the literature.The temperature distribution and NO_x emission were obtained.By studying the influence of different equivalence ratio,inlet velocity and inlet temperature on ammonia combustion flame,the emission rules and reasons of ammonia combustion flame under different conditions were obtained.When the equivalence ratio is 1,the temperature is the highest.The flame position moves downstream with the increase of the inlet speed,and the temperature gradient is obviously reduced.The NO production reached the peak value when the equivalence ratio was0.9,and rapidly decreased to a very low value when the equivalence ratio was 1.0-1.2.The reason is that a small amount of unburned NH₃ can reduce NO concentration in fuel rich condition.The effects of the thickness and radius of porous media on ammonia/air premixed combustion flame were studied.The reasons for the influence of various parameters on the stable combustion characteristics are obtained.The influence of the physical parameters of the porous media on the combustion performance was also investigated.The results exhibit that the porous medium with thickness of 8 cm and radius of 5 cm has a wide stable combustion limit.The increase in thermal conductivity and pore density will cause the flame to move upstream.In order to further improve the combustion performance of ammonia,this article also investigated the combustion performance of hydrogen doped with different contents.The results show that hydrogen doping can effectively increase the combustion speed and broaden the stability limit.After the addition of hydrogen,the NO emission increased,and the change trend with the equivalent ratio was basically the same as that of pure ammonia combustion.