Stirling Engine Cycle Characteristics And Heat Transfer Characteristics Of Stirling Engine's Porous Media Heaters

Stirling engine has a good adaptability to low calorific value gas,so Stirling engine has gained more and more attention of scholars.The phenomenon that the temperature of the Stirling engine heater is excessively heated during the heating of the flue gas in the free space cavity causes a “hot spot ablation” of the outer tube of the heater.Fortunately,the combustion of porous media can accelerate the combustion rate and evenly distribute the temperature of the flue gas in the chamber.This article first elucidates the system principle of the Stirling engine and the basic process of the Stirling cycle,and points out the advantages of the Stirling cycle over the Carnot cycle.Secondly,this article elaborates the difficulty of the current Stirling engine research,and focuses on the analysis of the “hot spot ablation” phenomenon when the Sterling heater is heated by the flue gas in the free space cavity.At the same time,this paper also analyzes the shortcomings of five cyclic analysis methods applied to the optimization design of Stirling engine.Based on the structure of Stirling engine free space combustion and heating chamber,this paper designs the symmetrical arrangement of porous medium combustion heating chamber structure on both sides of air inlet and gas inlet and symmetrical arrangement of air inlet and gas inlet center porous medium combustion heating chamber.In this paper,the heat transfer characteristics of the two chamber structures are simulated and analyzed.It is found that the former will distribute unevenly in the temperature of the flue gas inside the cavity with the increase of the gas inlet velocity,while the latter is even if the temperature distribution of the flue gas is uniform but the gas temperature is not high in the cavity.In view of this,this paper designs a Stirling engine tangentially-circular porous medium combustion heating cavity,and numerical simulation of the cavity from the temperature field,pressure value and velocity field.The simulation results show that the combustion cavity structure of the four-corner circular porous medium not only avoids the disadvantages of uneven temperature distribution in the free-space combustion flue gas,but also increases the temperature of the flue gas after combustion.This paper analyzes the combustion performance of each group by setting the control group from the factors such as gas inlet speed,equivalence ratio,porosity,and porous media type.The results show that the flue gas temperature increases with the increase of the gas inlet velocity.When the equivalence ratio increases,the flue gas temperature decreases.Flue gas temperature increases with increasing porosity from 0.725 to 0.825 and decreases with increasing porosity from 0.825 to 0.850.The temperature of flue gas varies greatly in different porous media,the temperature of nickel oxide is the lowest,and the temperature of zirconia is the highest.However,because the thermal conductivity of zirconia is as low as that of air in the free space,the temperature distribution of the flue gas in the zirconia combustion heating cavity is also uneven.In this paper,the relationship between temperature ratio,heater temperature,output power,and efficiency is deduced using finite-time thermodynamic analysis.The analysis results show that there is a maximum correlation between engine power and temperature ratio.The better the regenerative performance,the smaller the Stirling engine's required temperature ratio is,and the easier it is to reach the maximum power value.Stirling engine efficiency increases as the heater temperature increases,and the rate of increase tends to flatten as the temperature increases.