The influence of air distribution ratio on the fluctuation characteristics and stability of horizontal jet diesel non-premixed flame under extreme sub-atmospheric pressures.

• The flame probability fluctuation and flame stability are quantitatively related. • The vertical flame fluctuation parameter γ can reflect the flame stability in advance. • The flame trajectory equation is not affected by the proportion of secondary air. • The size and temperature variation of the flame recirculation zone are revealed. The burning problem in the plateau environment attracts more and more people's attention, and the plateau adaptability and flame stability of burner are the focus of recent research. The main purpose of this paper is to reveal the horizontal jet spray flame fluctuation characteristics and stability change rule under extremely low pressure (0.05 MPa) at a high altitude (about 5500 m) inhabited by human beings. Flame morphology and temperature properties were investigated in a low-pressure chamber with different secondary air ratios (23–53 %). It is found that the normalization of the flame trajectory equation is not affected by the ratio of secondary air. The temperature in the flame recirculation zone can be increased by 110 K as the proportion of secondary air increases to 45 %, but the maximum temperature is still lower than 1500 K. A continuous flame image processing method was implemented to define and analyze the flame fluctuation region. The results show that the dimensionless fluctuation parameter γ can predict the flame stability in advance than β. When the secondary air ratio is 40 %, the flame has the largest upward fluctuation; and when it exceeds 45 %, the flame stability becomes worse. This work is the first to obtain the results of the study on flame morphology and stability of horizontal jet spray flame distribution ratio under extremely low atmospheric pressure, which provides a theoretical scientific basis for the design of plateau burner, flame control, and flame stability improvement. [ABSTRACT FROM AUTHOR]