Downdraft Barbeque

Downdraft Barbeque
Peter Verhaart (Feb 7,99), Water Boiling Tests (Mar 6, 2002)

We have used it quite a few times now (we are not great barbecuers), it is quite convenient to operate. It typically takes 12 minutes to settle into smokeless and odourless combustion, our official propane fired bbq takes longer.

The fuel is bits of wood, 30 * 30 * 100 mm max size.The fire is lit on the grate, with a slide to adjust the active grate area. Since there are a few cheat holes in the riser pipe, the downdraft mode of burning starts automatically. The hot gases and flames flow from the riser and hit the underside of the bbq tray, which is a 10 mm steel plate. From there the gases leave through the chimney.


Downdraft Barbecue water boiling test 3/6/2002

Fuel as was 162 g
Fuel oven dry 140 g

Start Fire 9:48
Start Cook Time 10:05
End time 10:53

Initial fuel 2.6 kg
Remaining fuel 1.2 kg

Big pan dry 0.6 kg
Big pan + water 3.5 kg
Same after 2.8 kg

Small pan dry 0.7 kg
Small pan + water 2.2 kg
Same after 2.1 kg

Water temp start 26.2 C

Start boil big pan 10:28:00
Start boil small pan 10:48:00

Combustion value dry 21 MJ

Average Heat capacity water 4.2 kJ/kgK
Evaporation enthalpy 2257.6 kJ/kg

Average power output 8.82 kW

Heat from wood 25407.41 kJ

Heat into pans 3169.90 kJ

Efficiency 0.125 or 12.48 %