Burning Velocity of Turbulent Methane/Air Premixed Flames in Subatmospheric Environments.

The aim of our work was to study turbulent premixed flames in subatmospheric conditions. For this purpose, turbulent premixed flames of lean methane/air mixtures were stabilized in a nozzle-type Bunsen burner and analyzed using Schlieren visualization and image processing to calculate turbulent burning velocities by the mean-angle method. Moreover, hot-wire anemometer measurements were performed to characterize the turbulent aspects of the flow. The environmental conditions were 0.85 atm, 0.98 atm, and 295 ± 2 K. The turbulence-flame interaction was analyzed based on the geometric parameters combined with laminar flame properties (which were experimentally and numerically determined), integral length scale, and Kolmogorov length scale. Our results show that the effects of subatmospheric pressure on turbulent burning velocity are significant. The ratio between turbulent and laminar burning velocities increases with turbulence intensity, but this effect tends to decrease as the atmospheric pressure is reduced. We propose a general empirical correlation as a function between S T/S L and u'/S L based on the experimental results obtained in this study and the equivalence ratio and pressure we established.

Evaluation of the Energy Density for Burning Disaggregated and Pelletized Coffee Husks.

Coffee husks represent about 12 wt % of coffee grains, generating a significant impact on the environment because of its inadequate disposal. In Colombia, this waste presents an energy resource opportunity equivalent to over 49,106 TJ per year. However, several challenges related to this type of biomass, such as the moisture content, the irregular shapes, and the low bulk density, make its use difficult in current burners. Thus, in this paper, the combustion of coffee husk pellets was studied in detail to design a high-efficiency burner to produce energy for coffee drying. The pellets were prepared in a pelletizer with 15% moisture and 20% yield and burned in a bench-scale lateral reactor to determine the energy density. It was found that the combustion properties of coffee husk depend on the specifics of the pelleting process. The energy density values were I v = 0.789 MW/m3 and I g = 0.007 MW/m2, which could be used to design the combustion chamber for coffee husk burning.