Akane Uemichi

Combustion mechanism of ultralean rotating counterflow twin premixed flame

In our previous numerical studies [Nishioka Makihito, Zhenyu Shen, and Akane Uemichi. “Ultra-lean combustion through the backflow of burned gas in rotating counterflow twin premixed flames.” Combustion and Flame 158.11 (2011): 2188–2198. Uemichi Akane, and Makihito Nishioka. “Numerical study on ultra-lean rotating counterflow twin premixed flame of hydrogen–air.” Proceedings of the Combustion Institute 34.1 (2013): 1135–1142]. we found that methane– and hydrogen–air rotating counterflow twin flames (RCTF) can achieve ultralean combustion when backward flow of burned gas occurs due to the centrifugal force created by rotation. In this study, we investigated the mechanisms of ultralean combustion in these flames by the detailed numerical analyses of the convective and diffusive transport of the main species. We found that, under ultralean conditions, the diffusive transport of fuel exceeds its backward convective transport in the flame zone, which is located on the burned-gas side of the stagnation point. In contrast, the relative magnitudes of diffusive and convective transport for oxygen are reversed compared to those for the fuel. The resulting flows for fuel and oxygen lead to what we call a ‘net flux imbalance’. This net flux imbalance increases the flame temperature and concentrations of active radicals. For hydrogen–air RCTF, a very large diffusivity of hydrogen enhances the net flux imbalance, significantly increasing the flame temperature. This behaviour is intrinsic to a very lean premixed flame in which the reaction zone is located in the backflow of its own burned gas.

Combustion Oscillation Characteristics of Hydrogen-Rich Fuel

In this study, combustion oscillation characteristics of hydrogen-rich fuel were investigated. The experimental results fueled by mixture of natural gas and hydrogen show that hydrogen-rich combustion influences on the oscillating frequencies. In the case of only natural gas, the single oscillating frequency around 350 Hz is obtained, and in the hydrogen-containing fuel case, the double oscillating frequencies around 200 and 400 Hz are measured. However, the latter oscillating frequencies could not be derived from the one-dimensional acoustic analysis. Therefore, to figure out these frequencies, the acoustic impedance was measured experimentally and the oscillating frequencies were re-calculated using the measured acoustic impedance as the acoustic boundary conditions. As a result, the 200, 350, and 400 Hz frequencies could be expressed using the acoustic impedances.