Numerical Simulation On Catalytic Combustion Characteristic Of CH₄/Air Premixed Combustion In Opposed Flow Micro-combustor

Micro devices,such as sensors,micro air vehicles,micro medical devices,micro-pumps,micro reactors have been playing an important role on human life and production.Sustainability micro power device has been the key development of micro devices.With the advantages of high power density,portable,longevity,micro combustor draws more and more attentions of researchers.The fuel,methane,has the advantages of low carbon content,high calorific,abundant reserves and cheap,is beneficial for the popularization and application of micro power device in future.Combustion in micro combustor is hard to maintain stability and high efficiency,because the rate of heat loss increase sharply and the time during which fuel traverses through the combustor short significantly.Hence,it is necessary to study on catalytic combustion characteristic of CH4/Air premixed in micro combustor,providing the basis for the application of micro power device in the future.In this paper,the opposed flow combustor is been presented to solve the problems in micro combustor,such as the residence time of fuel,the inlet mode,and the preheating mode.The paper analyzes the influence of inlet velocity,equivalence ratio,heat dissipation and thermal conductivity on the combustion characteristic in different micro combustors.The structure optimization of opposed flow combustor is completed.The effect of inlet width L2,the length of the downstream L1,the inlet length of the downstream L3 and the inlet height of the downstream H on the combustion characteristic is analyzed.The numerical results show that the opposed flow combustor uses the opposite velocity of premixed inlet fuel and exhaust to realize opposed and prolong the residence time of premixed in combustor.Thus,the CH4 conversion and stable combustion range were improved significantly.The CH4 conversion of opposed flow combustor is 80.30% while the plate combustor is 67.99% at inlet velocity 1.1m/s,which increases 18.11%.The increase of the convective heat transfer coefficient will decrease the reaction rate of the methane and narrow the combustion stability limit,while the CH4 conversion is increased.The coefficient of thermal conductivity has dual effects on the combustor,which can improve the inlet preheating temperature and the outlet temperature of the exhaust.The influence of geometric parameters of opposed flow combustors on combustion characteristic is numerically simulated.The results show the inlet width L2 and the inlet length of the downstream L3 have significant influence on inlet velocity limit and CH4 conversion.Corresponding with L2=1.0mm,the inlet velocity limit of L2=0.1mm increases 34%,while the CH4 conversion increases 8.7% at inlet velocity 2.1m/s.Changing the inlet width L2 can adjust the distribution of premixed in the combustor,and increase the inlet length of downstream L3 and inlet height of downstream H can inhibit the premixed input significantly.The inlet width L2 and the height H have a great influence on the velocity field and opposed area.The research in this paper provides further theoretical basis for the design of high efficiency and stable combustion micro combustor,and has obtained some research results which have important significance and practical reference value.