[Group Combustion]
Elucidation of Flame Spread and Group Combustion Excitation Mechanism of Randomly-distributed Droplet Clouds

RESEARCH OVERVIEW

• The understanding of the mechanism of the combustion of liquid fuel spray is one of the most important issues in combustion science. In spray combustion, a burning state called “group combustion”, inside which one flame surrounds many droplets, occurs depending on various conditions. Excitation of group combustion, which is important for stable combustion of spray, would be caused by flame spread among fuel droplets. For better understanding and prediction of spray combustion behavior, therefore, it is essential to clarify flame spread mechanism of fuel droplets by using microgravity environment which enables employment of relatively larger droplets than those in real sprays.
• Flame spread phenomena of fuel droplet clouds are observed in detail for verification of the hypothesis which are related to flame spread characteristics of fuel droplets. n-decane (C10H22) is employed as fuel. Fuel droplets are deployed on crossing points of Silicon Carbide (SiC) fiber lattice (30 x 30, diameter: 14 micrometer) or on single SiC fiber (diameter: 78 micrometer). An edge droplet is ignited by electrically heated wire to initiate flame spread among droplets. Effects of droplets arrangement, droplet interval, and initial droplet diameter on flame spread phenomena are investigated. Obtained data will be compared with prediction by a proposed flame spread model.
• Microgravity environment provides us several advantages for the present investigation. The largest merit is magnification of the relevant physical scale such as droplet diameter and droplet interval as well as time scale such as the necessary time for flame to spread between droplets can be possible without induction of natural convection. So, space experiments are expected to reveal the nature of flame spread among fuel droplets through detail and precise observation of well-defined configuration. The findings and knowledge obtained through space experiment is applied to improvement of theoretical and numerical model to treat flame spread behavior among fuel droplets. Finally, it is expected that such model enables us improved prediction of complicated bahavior of spray combustion, leading to design of advanced spray combustors such as aero engines, gas turbines, and industrial furnaces.

SPACE APPLICATIONS

Rocket engines widely use spray combustion of liquid propellants immediately after injection into the combustion chamber. The high speeds of fuel and oxidizer as they move through the combustion chamber make it virtually impossible to analyze the droplet and flame interactions. Group Combustion will help improve numerical simulations used to predict spray combustion behavior in development of advanced rocket engines.

EARTH APPLICATIONS

Group Combustion will help improve flame-spread modeling for better prediction of spray combustion in cleaner, energy-efficient engines. It will provide clear guidelines for designing a spray combustor with stable combustion and bridge theory between droplet and spray combustion.

MIKAMI Masato [Yamaguchi University]