Investigations On Micro-channel Combustion Characteristics And Micro Free Swing Engine Systems

With the development of miniaturization of portable electronic products,it puts forward higher requirements for the energy supply system.At present,the mainstream power supply unit in the market is the battery.However,the energy density of batteries is low,the charging time is long,and the waste batteries are not friendly to the environment.Therefore,it is urgent to develop the energy supply system with high energy density,long discharge duration and fast charging.The energy density of hydrocarbon fuel is very high and easy to carry.The products after the hydrocarbon fuel combustion are carbon dioxide and water,which have no pollution to the environment.When the conversion efficiency of micro heat engine power generation system based on hydrocarbon fuel combustion is 3%,its energy density can be compared with the most advanced lithium battery in the world,and it is the most potential energy supply unit as an alternative battery at present.Because of its simple structure,less moving parts,high power density,convenient miniaturization,self-starting and no dead point in operation,the micro free swing engine has been widely concerned,and it is the best choice of power equipment for micro heat engine power generation system.This paper mainly focuses on the experimental and numerical research of micro free swing engine system,the specific contents are as follows:In the first part of Chapter 2,the experimental platform of microchannel flame propagation characteristics is introduced in detail,and the control equation and simulation method for numerical study of microchannel flame propagation characteristics are given.The second part mainly introduces the experimental equipment of the micro free swing engine system,and based on the first law of thermodynamics,the zero dimensional mathematical model of the micro free swing engine is established.The reliability of the zero dimensional model is verified by the experimental results.In Chapter 3,effects of tube diameter and equivalent ratio on flame propagation characteristics of lean ethylene/oxygen mixtures in millimeter-scale cylindrical tubes were experimentally investigated.Five different flame propagation modes including:（1）steady propagation mode（SPM）,（2）jerky flame mode（JFM）,（3）oscillating flame mode（OFM）,（4）oscillating flame transition to detonation（OFTD）and（5）jerky flame transition to detonation（JFTD）,are observed experimentally with the increase of equivalent ratio.The results show that the oscillation characteristics strongly depend on the tube diameter and mixture composition.The results show that the smaller the diameter of the tube,the more regular and smaller the flame oscillation cycles and amplitude,and the greater the influence of the heat loss on flame propagation.Under the same tube diameter,the ratio of the heat loss to total chemical heat release rate in the five flame modes is:H_lossSPM>H_lossJFM>H_lossOFM>H_lossOFTD>H_lossJFTD.The coupling between the wall heat loss,wall friction,and the flame boundary layers contribute significantly to the observed different flame modes and the transition from deflagration to detonation.In addition,the numerical results show that under the condition of non-adiabatic wall boundary,the flow field of flame presents vortex structure and is more complex.Compared with the adiabatic condition,the wall heat loss is the main cause of flame oscillation.In Chapter 4,experimental and numerical studies are carried out around the micro free swing engine,and the scale effect analysis is carried out.The single cylinder experimental results show that There is an optimal ignition advance angle and equivalent ratio to maximize the efficiency of the engine,with a maximum thermal efficiency of 12.5%.Moreover,the leakage of the micro free swing engine is serious and it is the main energy loss term of the engine.The energy ratio of each part is:leakage loss>exhaust loss>heat loss>indicated work.The experimental results of single cylinder continuous operation show that the smaller the ignition advance angle is,the higher the pressure peak is.When the engine is ignited in advance,the peak fluctuation of engine pressure and swing is small,and the engine runs more smoothly.The output voltage peak value of the generator is 7.8V,and the output power peak value is 12.16W.With the decrease of ignition advance angle,the peak value of heat release rate moves to the dead point.Comprehensive efficiency,power,frequency and other factors,when the ignition advance angleΔis-0.36 and the equivalent ratio?=0.9,the single-cylinder continuous running performance of the micro free swing engine is optimal.The experimental results of the continuous operation of double cylinders show that the indicated efficiency and power decrease with the increase of the ignition advance angle.When the ignition advance angle is-0.62,the maximum output efficiency of the engine is 5.6%,the indicated power is70W,the frequency is 58.7Hz,and the peak output voltage of the generator is 9.0V.Generally speaking,when the ignition advance angle is-0.62 and the equivalence ratio is 0.9,the engine performance is the best.The results of the scale effect study of the free swing engine show that the power,power density and efficiency of the engine gradually deviate from the ideal curve trend with the decrease of cylinder size only considering the effect of leakage or heat transfer.The frequency of the engine is not affected by leakage or heat dissipation.The friction loss does not affect the performance of the engine.When considering the coupling of each loss,the power,power density and efficiency of the swing engine decrease with the cylinder size,and the acceleration deviates from the ideal cycle curve.The limit cylinder size of the engine is 44 mm.Considering the coupling of each loss,the relative leakage mass or heat loss factor decreases with the increase of cylinder diameter.When the cylinder diameter is more than 0.5m,the main reason for the decrease of engine efficiency is the heat loss.When the cylinder diameter is 0.044m⁰.5m,leakage and heat loss are the main reasons for the decrease of engine efficiency.