The Mimi Moto forced draft TLUD achieves around 1-2mg/min PM2.5 at high power without an appreciable amount of residence time, as seen below. The jets of forced air create a downward flow of flame but there is only 7cm between the top of the fuel bed and the bottom of the pot when starting the stove.
Experiments have shown that elevated temperatures shorten the combustion time for CO and PM 2.5. At 900°C the combustion time required for complete combustion is less than half that at 700°C for all studied biomass particles. (Li, 2016) At 900°C, a residence period of between 0.6 to 1 second resulted in close to complete combustion of well mixed CO and PM 2.5. (Lu, 2008, Yang, 2008, Grieco, 2011). Boman (2005) reports that high temperature (>850°C) in a 5kW combustion zone combined with air rich and well mixed conditions for 0.5-1.0 second in the post combustion zone resulted in an almost complete depletion of particulate matter. Interestingly, when temperatures are around 900°C the near complete combustion of CO and PM requires only short residence times of 0.5 second. During such conditions, the residence time in the post-combustion zone is of minor importance for minimizing the emissions of products of incomplete combustion. For optimal results, a residence time of 0.5 seconds is suggested.
The Mimi Moto forced draft TLUD is clean burning at 950°C with very limited combustion time. Perhaps the combination of 1.) Metering the right amount of wood-gas into the combustion zone 2.) Coupled with molecular mixing 3.) At around 950°C reduces the need for 4.) Longer combustion times?
C. Boman, A. Nordin, R. Westerholm, M. Öhman, D. Boström.
“Emissions from small-scale combustion of biomass fuels- extensive quantification and characterization.” Umeå University, 2005.
H. Lu, W. Robert, G. Peirce, B. Ripa, and L. L. Baxter. “Comprehensive study of biomass particle combustion.” Energy Fuels, 22, pp. 2826-2839, 2008. doi:10.1021/ef800006z
Y. B. Yang, V. N. Sharifi, J. Swithenbank, L. Ma, L. I. Darvell, J. M. Jones, et al.
“Combustion of a single particle of biomass.” Energy Fuels, 22, pp. 306-316, 2007. doi:10.1021/ef700305r
E. Grieco, G. Baldi. “Analysis and modelling of wood pyrolysis.” Chemical Engineering Science, 66 (2011), pp. 650-660
E. Hroncova, J. Ladomersky, j. Valicek, L. Dzurenda. “Combustion of Biomass Fuels and Residues: Emissions Production Perspective.” Developments in Combustion Technology, 2016 DOI: 10.5772/63793
J. Li, M. C. Paul, P. L. Younger, I. Watson, M. Hossain, S. Welch. “Prediction of high-temperature rapid combustion behavior of woody biomass particles.” Fuel, Vol. 165, (1 February): 205-214, 2016.