Numerical Simulations On The Catalytic Combustion Of DME In Micro Tubes

With the rapid development of the modern portable electronic device,the energy system which can supply power for a long time is needed to match it.The energy density of the micro energy system is enhanced remarkably,thus the working time is prolonged greatly.The core of the micro energy system is the micro combustion.Micro combustion not only can be applied well in the portable electronic device,but also has an important application area in the aspect of national defense.This paper takes DME as the research object,focuses on the study of catalytic combustion characteristics of dimethyl ether in micro tubes.Dimethyl ether catalytic combustion characteristics in small scale,size effects and catalyst spatial density effects are investigated by means of CFD simulation.Micro-cylindrical packed bed combustor can not only realize catalytic combustion but also stable internal flow field and temperature field,dimethyl ether has good combustion performance and low emissions.The method of numerical simulation which is effective and can save resources was adopted,to establish the model of dimethyl ether combustion over Pt catalyst in micro-cylindrical packed bed burner,and investigate the optimal working condition to bring about the subsequant gas phase reaction.The research shows that when velocity is between 0.2 and 1 m/s,equivalent ratio is smaller than 1,catalytic combustion is better;when velocity is faster than 3 m/s,equivalent ratio is bigger than 3,it's better to cause gas phase reaction.The ignition temperature of dimethyl ether on Pt is 378 to 380 K.It is verified that the adsorption ability of dimethyl ether over the catalyst is stronger than that of oxygen.Moderately increasing oxygen concentration can promote the catalytic reaction,and excess dimethyl ether may inhibit it.The numerical simulation and comparison research of DME catalytic combustion in micro tube channels which diameters arel,2,4 and 8 mm.The results show that DME/air catalytic combustion stable combustion velocity upper limits have similar laws in tubes with diameters of 2,4 and 8 mm.When equivalent ratio is low,stable combustion upper limits are lower,and with the increase of equivalent ratio,stable combustion upper limits become higher.The lower limit of stable combustion is greatly influenced by diameter.The smaller the diameter is,the bigger the stable combustion lower limit is.For the lower limit of stable combustion,equivalent ratio influences more in big diameters,while flow velocity and equivalent ratio influence together in small diameters.For the upper limit of stable combustion,flow velocity influences more in big diameters,while equivalent ratio influences more in small diameters.Under the same condition,the conversion rate of DME/air is greatly influenced by the flow velocity in tubes with different diameters.When the diameter is bigger,the difference of conversion rate under different flow velocity is bigger.High flow velocity has a great influence on tubes with big diameters.Arrange 40mg catalysts uniformly for length of 10,20 and 40mm separately,then micro tube combustors with different lengths are getted.Comparison research of DME catalytic combustion in these micro tube channels by numerical simulation is conducted.The results show that the denser the catalyst spatial density is,the higher the stable combustion upper limit is.Increasing the density of the catalyst shortens the length of the catalytic area and decreases the residence time of fuel/air flow in the catalyst greatly.When the catalyst spatial density is different,the lower limits of stable combustion have no difference under high equivalent ratio,but have great differences under low equivalent ratio.Under the condition of low equivalent ratio and low flow velocity,the denser the catalyst spatial density is,the lower the stable combustion lower limit is.When the flow velocity is low,the activity of catalyst per unit volume has great effect on catalytic combustion.When the flow velocity is high,the combustion efficiency of the reactor is controlled by residence time of reactants.