Characteristics of premixed hydrogen/air squish flame in a confined vessel

The appearance of the squish flame is of great significance to accelerate burning progress and improve the combustion efficiency. In this paper, we experimentally studied the characteristics of the squish flame in a cylindrical constant volume vessel under different initial pressures and equivalence ratios by using high-speed schlieren photometry. Due to the compression of the main flame front, “squish flow” was induced in the analogous triangular vertebrae region besieged by the convex flame front, the concave wall and the flat optical windows, which provided the perturbation of large wavelength to promote the appearance of the squish flame. When the squish flames occur, as the initial pressure increases, the main flame propagation distance becomes shorter, the main flame propagation velocity increases first and then gradually saturates to a certain value; as the equivalence ratio increases, the main flame propagation distance becomes longer, the main flame propagation velocity rises first and then declines, and the maximum is obtained in the vicinity of Φ = 1.0. There exists a critical initial pressure at each equivalence ratio below which no squish flame appears, and it takes on a U-shaped trend with the increase of equivalence ratio. The hydrodynamic instability plays a key role in the formation of the squish flame. The squish flame tends to appear at higher hydrodynamic instability. The formation mechanism and the critical feature of the squish flame obtained in this paper can provide a theoretical guide to achieve fast controllable combustion.