Development of a wood-fired cooking stove to incorporate a thermo-acoustic engine-generator unit Ron DennisProf. Keith PullenCity UniversityLondon

Introduction City University has been responsible mainly for stove development This includes development of stoves to test thermo-acoustic engines (TAE) developed by other members of the SCORE group and carrying out the testing This paper describes the development of the general concepts of the stove design and specifically of a stove in which the TAE is placed vertically above the stove combustion chamber (CC) with heat transfer principally by radiation

Aims of SCORE project Develop a wood-fired cooking stove for domestic use that: 1Produces 100W of electricity for up to 4 hours per day 2Boils 3l of water in 15 minutes 3Reaches 50% of full power in 20 minutes 4Reduces wood consumption by 20%, compared to traditional stoves, to less than 1.4kg/hr 5Has low emissions

Initial Design Concept 1Heat initially to TAE then to cooking 2Acceptable to users – use Rocket Stove principle used widely in improved stoves. L- shaped combustion chamber – Horizontal leg to feed wood and air Vertical leg to draw in air and mix with wood gases for good combustion 3Radiation of 2kW to TAE from 300mm disc on top of combustion chamber (CC) 4Exhaust gases from CC pass through cooking section then to chimney to minimise emissions 5Two cooking pots, one cooking, one simmering 6Low thermal mass

Initial Design 80% Vermiculite/20% Cement Octagonal CC to fit 300mm disc 20mm fireclay on 20mm cast tile Two recessed pots, 200 mm diameter; 10mm gap under pot, 20 mm gap around pot Wood Air

Instrumentation

Test Set-up

Test Results Comparison of Temperatures for Combustion Chambers with Different Cross-section Areas Wood burn rates: Large CC (290mm dia.) – 2.5 kg/hr Small CC (140mm dia.) – 1.5 kg/hr

Conical Combustion Chamber Combustion chamber Ceramic or stainless steel Top ID – 300mm Bottom ID – 200mm Height – 135mm Firebox Vermiculite/cement Coated on inside with fire cement Disc sits on top of conical Combustion chamber Exhaust

Test Results Temperatures for Various Combustion Chamber Materials Wood burn rate 1.5 kg/hr

Heat from Combustion of 1 kg of Wood

CO Emissions

Summary Of Results

Summary of Progress Performance criterionTargetAchieved to date 1 Heat to TAE2 kW1.08 kW 2 Boil 3l of water15 minutes27 minutes 3 Reach 50% power – 90% temperature 945 o K in 20 minutes 895 o K in 25 minutes 4 Wood consumption reduced 20%< 1.4kg/hr1.5 kg/hr 4 Low emissionsMinimise smoke Achieved with chimney 5 Stove efficiency50%29.5%

Conclusions 1 Combustion Probably approaching best that can be achieved for domestic stove with varied type and condition of fuel One improvement in testing will be to adapt rig to use longer pieces of wood for more continuous combustion Stainless steel CC probably not durable and need to find better material 2 Cooking Improvement needed. Limit is area in contact with gases for convection. Can be considerably increased by ribbed hotplate which also has other significant advantages. Aluminium heat sink being tried 3 Stove design Concept is for heat-resistant inner shell of low thermal mass well insulated with lightweight insulation (probably wool), contained in robust, low-cost case (probably concrete blocks)