Diffusion flame

About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.

Experimental investigation on the self-ignition of pressurized hydrogen released by the failure of a rupture disk through tubes

Abstract: Hydrogen is expected to be used as a clean energy carrier. However, when high-pressure hydrogen is suddenly released into the air through tubes, self-ignition can occur by a diffusion ignition mechanism. In this paper, the phenomena of self-ignition and flame propagation during the sudden release of high-pressure hydrogen were investigated experimentally. Experimental results show that self-ignition can occur when bursting pressure is sufficiently high in spite of the shortness of the tube. For example, self-ignition was observed at a bursting pressure as high as 23.5 MPa with 50 mm long tube. When self-ignition successfully occurs, a hydrogen jet flame is produced by the ignition. The flame is then stabilized at the tube outlet. From photodiode signals and flame images, the propagation of a flame inside the tube is confirmed and the flame is detected near the rupture disk as the bursting pressure increases. When the tube length is not long enough to produce self-ignition, a hydrogen flame is observed in the only boundary layer at the end of tube and it quenches after the flame exits the tube. Consequently, the formation of a complete flame across the tube is important to initiate self-ignition, which sustains a diffusion flame after jetting out of the tube into the air. Also, in order to establish a complete flame across the tube, it is necessary to have sufficient length such that the mixing region is generated by multi-dimensional shock–shock interactions.

Entropy Generation in a Confined Laminar Diffusion Flame

Abstract: A theoretical model for the rate of entropy generation has been developed for an axi-symmetric laminar diffusion flame in which a cylindrical fuel stream is surrounded by a co-flowing oxidizer jet in a confined environment. The solution for the diffusion flame is generated by solving the mass, momentum, energy and species conservation equations, simultaneously, using a finite difference method with the appropriate boundary conditions. A single step global reaction kinetics between fuel and oxygen is considered for the solution. The effects of varying the inlet air temperature and the air-fuel ratio on the total rate of entropy generation as well as the contribution of the individual subprocesses towards entropy generation are investigated.

Two Stage Ignition of n-Heptane Isolated Droplets

Abstract: Experimental and theoretical studies on the spontaneous ignition process of isolated fuel droplets were carried out. Time dependent temperature fields around the igniting droplets were observed by interferometry so that two step temperature rise can be detected. Some experiments are performed under microgravity to obtain reference data. Induction times are examined as a function of ambient temperature. As a result, a zero temperature coefficient region is found, which is equivalent to the NTC (negative temperature coefficient) region for the ignition of premixed gas. A numerical model is developed applying a simplified chemical reaction model that includes the low and the high temperature reactions. The model is able to reproduce the two step temperature rise and the roles of the two kinds of reactions on the ignition process up to the establishment of a diffusion flame around the droplet are examined.