An experimental study of combustion characteristics of hydrogen–Air pre-mixture on the wall boundary condition

By means of the Schlieren method, the combustion characteristics of hydrogen–air pre-mixture on wall boundary conditions have been studied in a constant volume combustion cell with ignition point located in the upper part of the cell. The results indicated that the restrictive combustion process of the pre-mixture can be divided into four stages: the laminar flame stage, the cellular flame stage, the squish flame stage and the auto-ignition stage. The squish flames appear on both sides of the main flame under most of the experimental conditions. The appearance of squish flames can cause a fluctuation in pressure change rate. The lower the equivalence ratio is, the earlier squish flames appear spatially and the less the auto-ignition is prone to present itself. The lower the initial pressure is, the more difficultly the squish flames present themselves. As the initial pressure drops, the combustion tends toward directly enter into the auto-ignition stage from the laminar flame stage. The higher the initial pressure is, the earlier the auto-ignition presents itself spatially. Squish flames experience two processes of formation and spread. The restrictive effect of the wall could be a factor that impacts on squish flames.