Happy Holidays Clean Combustion Techniques

Happy Holidays Clean Combustion Techniques

1.)    When wood is burned a lot of smoke is produced but the made charcoal at the tip of the wooden stick contributes heat but does not make much smoke. Rocket Stove: Increase the time that the charcoal at the tip is burning. TLUD: A layer of hot charcoal covers the fresh wood.

2.)    If the stove begins smoking the rate of reaction (solid turning into gas) is probably too fast. Too much wood gas is being produced and un-combusted fuel is escaping. Rocket Stove: Pull the sticks back until just the tips are burning. TLUD: Reduce the primary air.

3.)    Mixing the smoke, gases, flame, and air can reduce emissions dramatically. Rocket Stove and TLUD: Cut up the laminar flames with natural draft mixing devices. When using secondary air increase the draft until fast moving jets completely cover the top of the burning fuel.

4.)    Create a space filled with fire that forces the smoke, gases, flame, and air to mix more completely. Rocket and TLUD: Orifices successfully increase mixing.

5.)    Increase the dwell time to improve combustion efficiency. Rocket and TLUD: Do not make the mixing chamber above the fire too short. With sufficient draft install fixed fan blades to induce swirl that makes at least two revolutions.

6.)    Secondary air more effectively enters flame when the pressure difference is assisting the mixing process. Rocket and TLUD: In natural draft stoves the pressure is lower in fast moving flame. Add higher pressure secondary air downstream of the mixing device.

filter setup

HEPA home furnace filter reduces PM2.5 emissions

HEPA home furnace filter reduces PM2.5 emissions

There are a number of methods to reduce personal exposure to household air pollution associated with using biomass fuel for the daily cooking and heating taking place in nearly 40% of global households. These most commonly include 1.) Increasing ventilation rates, 2.) Installing a chimney and 3.) The use of cleaner fuels and cook stoves. A recent ARC paper available (free for a limited time) at:


investigates two less-commonly considered methods: 1) Reducing exposure through filtration and capture of PM2.5 and 2) Avoiding making emissions by using made charcoal and retained heat for cooking.

filter setup

The smoke is pulled through the filter and less smoke exits the room

When cook stoves are operated inside an enclosure from which smoke is pulled through an inexpensive HEPA-type furnace filter before exiting to the outside, the personal exposure levels, room concentrations, and external pollution are reduced. To test this method, an enclosure was built from which a box fan pulled the air and PM2.5 through four different furnace filters. The rate of PM2.5 production (mg/min) exiting the filter was monitored with gravimetric measurement under a LEMS emissions hood during the high and low power phases of the Water Boiling Test 4.2.3 conducted on a biomass rocket stove with forced draft.

The average of seven baseline emissions tests with no filter was 7.5 mg/min of PM2.5. The average of seven tests using the highest quality furnace filter (3M 2200) was reduced to 1.5 mg/min and the difference was significant at 95% confidence. The use of retained heat to simmer dramatically reduced emissions of PM2.5 by burning the boil-phase-made-charcoal and using retained heat in the stove while 5 liters of covered water were simmered for 35 minutes.