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Microgravity Science and Technology

, Volume 30, Issue 4, pp 419–433 | Cite as

Flame Spread and Group-Combustion Excitation in Randomly Distributed Droplet Clouds with Low-Volatility Fuel near the Excitation Limit: a Percolation Approach Based on Flame-Spread Characteristics in Microgravity

  • Masato Mikami
  • Herman Saputro
  • Takehiko Seo
  • Hiroshi Oyagi
Original Article

Abstract

Stable operation of liquid-fueled combustors requires the group combustion of fuel spray. Our study employs a percolation approach to describe unsteady group-combustion excitation based on findings obtained from microgravity experiments on the flame spread of fuel droplets. We focus on droplet clouds distributed randomly in three-dimensional square lattices with a low-volatility fuel, such as n-decane in room-temperature air, where the pre-vaporization effect is negligible. We also focus on the flame spread in dilute droplet clouds near the group-combustion-excitation limit, where the droplet interactive effect is assumed negligible. The results show that the occurrence probability of group combustion sharply decreases with the increase in mean droplet spacing around a specific value, which is termed the critical mean droplet spacing. If the lattice size is at smallest about ten times as large as the flame-spread limit distance, the flame-spread characteristics are similar to those over an infinitely large cluster. The number density of unburned droplets remaining after completion of burning attained maximum around the critical mean droplet spacing. Therefore, the critical mean droplet spacing is a good index for stable combustion and unburned hydrocarbon. In the critical condition, the flame spreads through complicated paths, and thus the characteristic time scale of flame spread over droplet clouds has a very large value. The overall flame-spread rate of randomly distributed droplet clouds is almost the same as the flame-spread rate of a linear droplet array except over the flame-spread limit.

Keywords

Flame spread Group combustion Droplet cloud Percolation Microgravity 

Notes

Acknowledgments

This research was partly subsidized by JSPS KAKENHI Grant-in-Aid for Scientific Research (B) (24360350 and 15H04201). We would like to acknowledge the assistance by Mr. Hisashi Shigeno, Mr. Yuki Tsuchida and Mr. Daiki Azakami. This research was also conducted as a part of “Group Combustion” project by JAXA.

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Copyright information

© Springer Science+Business Media B.V., part of Springer Nature 2018
corrected publication March/2018

Authors and Affiliations

  • Masato Mikami
    • 1
  • Herman Saputro
    • 2
  • Takehiko Seo
    • 1
  • Hiroshi Oyagi
    • 1
  1. 1.Department of Mechanical EngineeringYamaguchi UniversityUbeJapan
  2. 2.Mechanical Engineering Education DepartmentSebelas Maret UniversityPabelanIndonesia

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