Plant Oil-based Cooking Stove: Primary Research Results

E. Stumpf, A. Esper, R. Baumann, and W. Mühlbauer

Institute for Agricultural Engineering in the Tropics and Subtropics,

Hohenheim University, Stuttgart, Germany

Abstract

In rural areas of developing countries, cooking is predominantly done on open fires. Wood scarcity urges intensified utilization of alternative cooking methods. At Hohenheim University a modified pressure cooker was developed, which utilizes plant oils like Jatropha oil as fuel.

INTRODUCTION

In rural areas of tropical and subtropical countries wood is still the main energy source. Steadily rising firewood consumption for cooking purposes results in deforestation of large areas creating severe ecological, economical and sociological problems. In order to protect the environment it is urgently required to utilized alternative methods for cooking purposes. Introduction of fuel-efficient stoves can significantly reduce the firewood consumption. However, the decrease in consumption will soon be compensated by the fast growing population. Electricity or kerosene is limited mainly to urban areas. Use of solar cookers and utilization of biogas are still limited due to technical and handling problems.

Plant oils like Jatropha oil are a promising alternative energy source offering a variety of economical and ecological advantages. Their utilization as cooking fuel would give another incentive to intensify cultivation of oil plants. Through locally processed plant oil decentralized structures are strengthened which provide employment and income opportunities for population. Moreover, a long-term supply of cooking energy can be secured. Collection time and purchase cost of fire wood, respectively, as well as deforestation will be reduced. Burning of plant oils is carbon dioxide neutral. The plant oils are bio-degradable so handling is both simple and danger-free.

LIQUID FUEL COOKING STOVES

Two basic principles are common practice for combustion of liquid fuels for cooking stoves like kerosene. In general, wick-type cookers have lower efficiencies and lower power output than pressure-type cookers. Wick stoves utilize the capillary effect of fluids. Since plant oils have a very much higher viscosity than kerosene, common wicks cannot maintain the oil supply and the flame extinguishes. Therefore primary investigation concentrate on pressure burners. They require a certain pressure in the fuel tank. Fuel evaporates in the vaporizer and emits through a nozzle into the combustion area where it burns by mixing with ambient air.

PRIMARY DESIGN OF A PLANT OIL COOKING STOVE

At the Institute for Agricultural Engineering in the Tropics and Subtropics of Hohenheim University a primary plant oil cooker was developed. Investigations were based on a pressure kerosene stove originally designed for camping purposes. Through proper modification continuous operation of the stove for more than 5 hours is possible. By construction of a novel vaporizer made from copper retention time of the plant oil within the flame was increased considerably. By increasing the number of air holes sufficient air supply is ensured to maintain the combustion process.

The cooker was successfully operated with Jatropha oil as well as with sunflower, rape and corn oil. Since plant oils have high ignition points, kerosene is still required to start-up the cooker. After 2 to 3 minutes operating temperature is reached and fuel supply of the cooker is switched to plant oil. For closing down operation the stove needs to be fueled with kerosene again enabling a problem-free start the next time. For easier handling, a two tank system was designed. One fuel container contains the plant oil while the smaller tank is filled with kerosene.

Even though results are promising, further research is necessary in order to overcome existing problems. Heavy visible emissions occur especially during start-up and close-down. Since plant oils dissociate at temperatures below boiling temperature cracking occurs. The cracking products clog vaporizer and nozzle. Thorough cleaning and frequent exchange of the vaporizer are required. Moreover, a special ignition device is needed allowing reduction of ignition time and amount of kerosene required.

The proposed design is preliminary for research purposes only. Handling is still rather difficult and not acceptable for broader dissemination. For successful introduction into developing countries the to be designed cooking stove should meet specific design criteria. Among others a simple maintenance, a high efficiency and an easy power regulation are required.

last modification  21.06.02   by