Effect Of Adding Ozone On Detonation Wave Propagation Characteristics Of CH₄-O₂ Premixed Gas

Pulse detonation engine is a propulsion system based on periodic impulse generated by detonation combustion.It uses high-temperature and high pressure gas generated by intermittent or pulsed detonation waves as its power.It has the advantages of high thermal cycle efficiency,simple structure,high specific impulse,low cost and wide application range.It is one of the ideal powers for high-speed aircraft in the future.How to form a stable detonation wave is a technical problem for pulse detonation engines.Deflagration to detonation transition（DDT）is one of the commonly used methods.In order to shorten the DDT distance,in this paper,the propagation characteristics of detonation waves were experimentally studied using high-speed photography technology in a round glass pipe with a length of 1 m and inner diameters of 3 mm,5 mm,and 7 mm.The flame front propagation diagram of the premixed gas burning in the pipeline was obtained;the effects of adding ozone on the detonation wave initiation distance and flame propagation speed in the methane-oxygen premixed gas were analyzed carefully.The main research conclusions and innovations of this article are as follows:（1）Explore the effect of initial pressure on the flame propagation characteristics of 1CH₄+2O₂ premixed gas.In a 3 mm pipe,the flame propagation characteristics of the pipe under the condition of fuel-oxygen stoichiometric ratio were studied.It was found that with the decrease of the initial pressure,the propagation state of the flame in the pipeline showed an unstable detonation propagation mode with a large velocity oscillation,a galloping detonation propagation mode,and a rapid flame propagation mode.As the pressure increases,the flame initiation distance（DID）continues to shorten,the average flame propagation speed continues to increase,and the detonation wave speed loss becomes smaller and smaller.（2）The influence rule of adding hydrogen on flame propagation characteristics of methane oxygen premixed gas is obtained.In 3 mm pipe diameter,the methane oxygen mixed mass fractions of 4%,11%,33%,and 100%hydrogen mixed in the equivalence ratio were used to study the effect of hydrogen concentration on flame propagation characteristics.The results show that when the initial pressure is the same,the higher the hydrogen concentration in the mixed gas,the faster the average flame propagation speed after the flame is stabilized,and the shorter the detonation distance of the detonation wave;the higher the hydrogen concentration,the lower the pressure of critical detonation limit,the smaller the unstable detonation zone.（3）The effect of adding ozone on the propagation characteristics of detonation wave of methane/oxygen premixed gas is obtained.In pipes with diameters of 3 mm,5 mm,and 7 mm,the mixing volume ratio of methane/oxygen mixed according to the equivalence ratio is 0.44%,0.95%,1.4%,and 2%ozone respectively.The following conclusions were obtained:when the initial pressure was 40 kPa,as the ozone concentration increased,the detonation initiation distance continued to decrease,and the flame propagation speed continued to increase;under the same working conditions,the detonation distance with diameters of 5 mm and 7 mm is more shortened,that is,the larger the pipe diameter,the greater the effect of ozone on DID.The greater the initial pressure,the smaller the effect of tube on the propagation characteristics of the detonation wave,and the smaller the loss of flame propagation velocity under the same concentration of ozone.（4）The difference between the detonation initiation distances of detonation waves of the two premixed gases 1CH₄+2O₂ and 2CH₄+2H₂+5O₂ under the adding of ozone is compared.The results show that:compared with 1CH₄+2O₂ premixed gas,2CH₄+2H₂+5O₂ premixed gas is less affected by ozone.When the same concentration of ozone is added,the detonation initiation distance of 2CH₄+2H₂+5O₂ premixed gas is shortened shorter.After adding ozone,the critical pressure of detonation decreased accordingly.In a 7 mm diameter pipe,the critical pressure of detonation wave of1CH₄+2O₂ gas mixture is more affected by ozone than that of 2CH₄+2H₂+5O₂ gas mixture.