In order to investigate the influence of changes in oxygen fuel mixing ratio on the ignition performance,ignition process and flame structure size,CH4/O2 ignition experiments were carried out in this paper.Considering that the CH group is the main species that chemiluminescence signal when CH4 is burned,representing the start point of combustion chemical reactions and also an indicator of the distribution of combustion flame structure,so the flame structures under different oxygen fuel mixing ratios were photographed by using high-speed camera and CH based filter.The conclusions are as follows:Under different oxygen fuel mixing ratios,the flow mixing and ignition combustion conditions near the igniter vary,resulting in different ignition delay times.This is manifested as the time when the pressure begins to establish increases with the increase of oxygen fuel mixing ratio,and the ignition delay time decreases with the same ignition energy.Extending the time interval between valve opening and igniter operation increases the mass of unburned gas in the combustion chamber,leading to higher pressure peaks during ignition.In extreme cases,the flame directly expands significantly.The oxygen fuel mixing ratio has a great impact on the flame structure size in the pressure building process,which is mainly manifested in that the flame expansion angle and attenuation rate increase with the increase of the oxygen fuel mixing ratio.There is no obvious difference in the flame structure size in the stable section under different oxygen fuel mixing ratios,and the combustion stability is good.
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