Numerical Simulation On Catalytic Combustion Characteristic Of H₂/Air Premixed Combustion In Micro-combustor With Controllable Vortex Bluff Body Slotted At Two Sides

With the rapid progresses of micro-electro-mechanic system technology,various small devices,including micro aircrafts and portable electronic and communication devices,are continuously emerging for military,industrial applications and human daily lives.Combustion based micro power generation devices are considered to be one of competitive alternatives due to much higher energy densities of hydrocarbon fuels with advantages of high energy densities,small size and portability.The micro-combustor is a key component of micro-power generation system.Thus,the development of micro-combustors with a wide operational range has attracted increasing attention over last decade.Meanwhile,there are several challenges in micro-combustors.One of the most important issues is increased heat losses due to large surface area-to-volume ratio of micro-combustor.Another critical problem is shortened residence time of fuel under reduced dimension.And many unstable micro-flames such as extinction and flame splitting phenomenon have been reported to date.In this paper,the micro combustor with controllable vortex bluff body slotted at two sides is presented to solve problems of combustion instability.The paper analyzes the effects of inlet velocity,equivalence ratio and inlet temperature on combustion characteristic by detailed reaction mechanism of H₂/O₂.The structure optimization of combustor with controllable vortex bluff body slotted at two sides is carried out.The effects of controllable flow ratio?,controllable gap width d,controllable apex angle of bluff body?and controllable apex angle of airflow?on combustion characteristics,such as stability limits,efficiency,temperature and velocity distribution is analyzed.The higher velocity difference on both sides of controllable vortex bluff body slotted at two sides and the rear part of bluff body is used to further expand reflux area,enhance flow and heat transfer in fuel,and prolong residence time of fuel in combustor,which improve combustion efficiency and extinguishing limit.With the increase of inlet velocity,combustion efficiency of controllable vortex bluff body slotted at two sides is higher than that of traditional blunt body.The expansion of reflux zone on controllable vortex bluff body slotted at two sides will promote increase of increase in amplitude of combustion efficiency,but further increase inlet velocity,which leads to the increase of flow velocity on both sides of combustor,and unreacted fuel is easy to flow out,resulting in a decrease in combustion efficiency,resulting in a decrease in increase in amplitude of combustion efficiency.With the increase of equivalence ratio,the extinction limit and combustion efficiency of micro combustor with controllable vortex bluff body slotted at two sides and traditional bluff body show a tendency to increase first and then decrease.When the equivalence ratio is 1,the extinction limits of two combustors reach maximum value of 37m/s and 51m/s.On one hand,the increase of inlet velocity leads to an increase in heat loss.On the one hand,it also expands recirculation zone and enhances combustion rate of chemical reaction.Besides,the increase of equivalence ratio means increasing fuel consumption.The coupling between three causes two micro combustors to reach maximum at different inlet velocities under different equivalence ratios.When inlet temperature is increased,combustion efficiencies of two micro combustors are greatly improved.The influence of controllable vortex bluff body slotted at two sides parameters on H₂/air combustion characteristics are numerically studied.The research results show that increasing?or reducing d can obviously improve velocity of controlled airflow,which can expand recirculation zone and improve combustion efficiency.To further expand?or reduce the d,flow velocity of controllable gas is too large,which will result in increase of incomplete combustion heat loss and trend of reducing extinction limit.In addition,the too large d can leads to increase of fuel flow rate in main channel,and fuel flows out from both sides of combustor,leading to decrease of extinction limit.Increasing?or reducing?can significantly improve combustion efficiency.Because of changing in outlet direction of controllable airflow,radial velocity of controllable airflow increases,axial velocity decreases,and recirculation zone expands.Increasing?leads to increase of rear shear stress,resulting in extinction limit decreasing.Too large or small?can leads to the excessive axial or radial velocity of controllable flow and the reducing extinction limit.The stable combustion mechanism and mixing enhancement mechanism of H₂/air can be studied in this paper.It can achieve high efficiency,which lays a foundation for micro combustion technology,and has a good guiding significance for study on structure of micro combustion power.