The single most important device that calls for our immediate attention is the wood burning stove-choola - used for cooking in most of our houses. Since a large amount of firewood takes the route of cooking, it is imperative to look at this device first. Efficiencies of our choolas vary from 5-15%. Any further increase will help in reducing the firewood consumption and other associated problems. Three designs have been developed claiming to have better efficiencies. Two of them - Astra ole developed at IISc and Priagni developed at CPRI - are discussed in this report.

Astra Ole :

One of the important activities taken up by the Centre for Application of Science and Technology for Rural Areas, IISc has been in the field of cooking. As stated elsewhere, ASTRA has been looking at the rural cooking problem and trying to identify solutions - to improve the efficiency of cooking stoves, to use biogas for cooking etc.

A survey and experimentation by Geller showed that the efficiency of wood stoves is in the range of 10-15%. He also identified some areas of heat losses. Prompted by the large scale consumption of firewood in cooking and its scarcity. Professor Kumar and his group started the investigations on wood stoves. They started with the following assumptions;

i) Any new design should be based on the geometry of existing choolas;

ii) The stove should be made mostly from locally available materials by local people with minimum additional skills and with minimum training;

iii) The stove should accept local fuels - twigs, bark, husk, bagasse, stems etc;

iv) It should not cost more and it should not put any constraint on existing practices.

With the above conditions, the objectives chosen are;

i) ease of cooking;

(ii) minimisation of smoke;

iii) ease of starting and stopping the fire;

iv) maximisation of efficiency.

The stove designed is a three pan one, mostly made of mud - looking similar in appearance to existing stoves. There is an enclosed fuel box with a cover; the grate, and parts for primary air into the choolas; flow of fuel gas is controlled by the ducts between pans (1 and 2, 2 and 3) and chimney. The pan openings can be adjusted during construction so as to fit snugly the vessels used normally in the house.

To achieve the given objectives the following were modified or incorporated; (a) area of primary air inlet hole; (b) distances (heights) of combustion chambers; (c) flow diffuser for third pan; (d) orientation of fuel box; (e) materials used for construction and insulation of inner wall-mud and rice husk; (f) coating the grate with simple catalysts to facilitate cracking.

A number of models have been constructed and tested before arriving at an optimal model, ready for diffusion amongst villages. The production model named Astra ole was taken up for field tests - in the high rainfall Uttara Kannada district and the low rainfall Tumkur district. Results were encouraging. ASTRA put up about 100 stoves in Ungra and neighbouring villages. Field efficiencies were varied from 30% to 43% with a mean of 35.5%. This is nearly double that of a traditional stove (mean is 13.3%). Similarly, specific fuel consumption varied from 100 to 250 grams with a mean of 168 grams. The comparable figures for traditional stoves are 251 to 450 grams with a mean of 351 grams. Hence it is clearly shown that the people can save definitely half of the firewood used previously.

Similarly, Astra ole was constructed in large numbers by the Centre for Ecological Sciences, IISc., in Uttara Kannada district - both in the hilly Sirsi taluk and in the Coastal taluk of Kumta. Field studies of CES show similar results.

In addition it has also been found from field studies that the Astra ole is smokeless (so cooking is a pleasent activity for village women); it cooks faster - 40% lesser time for cooking than that of conventional ones, as flame is steady and continuous, no blowing of air is required - improves health of women doing cooking activities; various types of fuels can be used with ease.

Because of these proven advantages, the State Department of Science and Technology stepped in to take up the diffusion work. It gave primary importance to this activity and entrusted the district rural development societies the task of constructing a large number of Astra oles in all districts. As the first activity in diffusion is to generate skilled persons the Karnataka State

Council for Science and Technology (KSCST) has taken up the task of arranging training programmes. They have selected a number of persons as trainers. These were given comprehensive training. These trainers now conduct programmes in various places in all districts. Hence in a short while, it is expected to produce a large number of trained persons dispersed all over the State.

The Department of Sciences and Technology is coordinating the construction work. Targets have been set for each taluk/ district and subsidies under various programmes are also being distributed promptly to persons putting up Astra oles in their houses.

Priagni:

This is an improved wood burning stove designed by the Rural Energy Laboratory, Central Power Research Institute. It has been designed to improve efficiency, to create a steady and continuous flame for burning and to reduce smoke. It is an iron single pot stove modification of existing commercially available ones. The factors considered in design improvement are;

i) Proper height of the stove (combustion chamber) - low height means incomplete combustion and high height means more losses of atmosphere;

ii) Optimal diameter - to reduce smoke;

iii) Height of vessel mounts;

iv) Fuel feed opening - to reduce exposure of wood flames (thereby reducing radiation loss);

v) Grate design.

After optimisation of these parameters, two components have been added. The first is a set of two slotted plates - one at the top and the other at the bottom. The top plate creates turbulance, imparts velocity to the gasses and acts as a partial enclosure to combustion chamber. The bottom plate acts as an air inlet providing for symmetric air flow - helps in continuous burning of the fuel.

The second addition is a clip - on aluminium lining to the inner wall. The thin air gap between the stoves wall and the lining reduces heat flow to the walls, thereby increasing efficiency.

The stove was designed in 3-4 different sizes to cater to different family sizes. The costs vary from Rs. 35/- to Rs. 78/-. Because of its resemblance to existing stoves, it is easier to operate and so acceptability particularly amongst urban households is high. The State Department of Science and Technology took up the popularisation of this stove. It entrusted the manufacture of 750 stoves of this type to Government Workshop, Madikere. These stoves were distributed for field trials to a large number of persons. Two trials in an NSS Camp showed the advantages of this stove.