A study of flame spread along a droplet array at elevated pressures up to a supercritical pressure
✍ Scribed by Jeong Park; Hideaki Kobayashi; Takashi Niioka
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 700 KB
- Volume
- 23
- Category
- Article
- ISSN
- 0363-907X
No coin nor oath required. For personal study only.
✦ Synopsis
Experimental investigations on #ame spread along a droplet array have been conducted at elevated pressures up to supercritical pressures of the fuel droplet under normal gravity and microgravity. The #ame spread rate is measured using high-speed chemiluminescence images of OH radicals and direct visualization is employed to observe the images of the vaporizing fuel around the unburnt droplet.
The mode of #ame spread is categorized into two: a continuous mode and an intermittent one. There exist a limit droplet spacing and a limit ambient pressure in normal gravity, above which #ame spread does not occur. It is seen that #ame spread rate is dependent upon the relative position of #ame to droplet spacing. In microgravity, the limit droplet spacing of #ame spread and the droplet spacing of maximum #ame spread rate are larger than those in normal gravity. In microgravity, the #ame spread rate with ambient pressure decreases initially, shows a minimum, and then decreases again after taking a maximum. Flame spread time is determined by competing e!ects between the increased transfer time of the thermal boundary layer due to reduced #ame diameter and the decreased ignition delay time in terms of the increase of ambient pressure. In normal gravity, the #ame spread rate with ambient pressure decreases monotonically and there exists a limit ambient pressure, except at small droplet spacing, under which #ame spread extends to the range of supercritical pressures of fuel. This is because natural convection induces the upward #ow of hot gases into a plume above the burning droplets and limits the lateral transfer of thermal boundary layer. Consequently, it is found that #ame spread behaviour under microgravity is considerably di!erent from that under normal gravity due to the absence of natural convection.