Study on combustion in a small-scale channel that is equivalent to reaction zone thickness

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 16360096
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Thermal engineering
• Research Institution: TOHOKU University
• Principal Investigator: MARUTA Kaoru TOHOKU University, Institute of Fluid Science, associate professor, 流体科学研究所, 助教授 (50260451)
• Co-Investigator(Kenkyū-buntansha): SAKAI Seigo Yokohama National University, engineering, associate professor, 工学部, 助教授 (70323110) ; KOMIYA Atsuki TOHOKU University, Institute of Fluid Science, assistant, 流体科学研究所, 助手 (60371142)
• Project Period (FY): 2004 – 2005
• Keywords: Combustion / Reaction zone / Micro scale

Research Abstract

Understanding the combustion characteristics in a microchannel with heat recirculation is important for the development of micro scale combustors. However, small scales prevent the experimental approach. One possible solution for this problem is using of a micro channel under the low pressure conditions. By this, combustion in extremely small tube at normal pressure is expected to be simulated experimentally with meso-scall microchannels. Cylindrical quartz glass tube (i.d.=2.0) heated by flat flame burner which resembles heat recirculation was employed. Effects of pressure (0.06-0.6 atm), flow velocities, and methane-air mixture compositions at extinction limit were investigated.
1. A mild combustion under low pressure was observed both experimentally and numerically. Flame thickness at 0.2atm became ten times larger than that at normal pressure. Therefore, the combustion in extremely small tube which diameter was almost the same as flame thickness was realized. In general, the flame has the curvature near the quenching limit in normal scale tube. However, the present flame retained the flat shape and only became thick.
2. The experimental results showed the upper limits of flow velocity for fuel-lean side is larger than those for rich side, that is, the flammable region didn't become symmetric about stoichiometric ratio. However, the numerical simulation showed the flammable limit was largest near φ=0.8 and furthermore it is expected that upper limits for much leaner mixture become small.
3. Since the quenching Peclet number is very small, heat transfer to the wall is quite large. However, in this research, the flame could be stabilized because of small heat loss by external heating.
4. Close to blow off conditions at lean side, chemical reaction time is faster than that of rich side therefore the flame can be stabilized up to the high flow velocity. This is one interpretation for experimental result of flammable region.