Partners
- CIRAD
- University of Ouagadougou , Burkina Faso
- Centre national de la recherche scientifique et technique (CNRST), Burkina Faso
- Institut international d'ingénierie de l'eau et de l’environnement (2IE), Burkina Faso
Research units
Biomass and EnergyAgrofuels: vegetable oils are on a par with diesel
06/03/2009 - Article
While vegetable oils cannot be adapted to engines, there is no reason why engines should not be adapted to vegetable oils. The main question is how to go about it. A PhD student from Burkina Faso, jointly supervised by CIRAD, has just answered that question by determining the characteristics of efficient combustion of such oils.
Using vegetable oil in engines or boilers? What a ridiculous idea! This was what scientists thought until recently. The drops of such oil injected into engines are much too large compared to diesel. However, a PhD student from the University of Ouagadougou, jointly supervised by CIRAD, has just proved that on the contrary, vegetable oils could be suitable for use in engines or boilers. Two characteristics govern their suitability: their viscosity, and thus their temperature, and the temperature of the environment into which the oil is injected. Provided these two conditions are met in engines, vegetable oils perform in a similar way to domestic fuel oil.
Granulometry is what really governs good combustion: the aim is to obtain as fine an oil spray as possible, to ensure that the droplets evaporate efficiently. The researchers involved began by studying the correlations between the physicochemical characteristics of different oils, notably their viscosity, droplet size, evaporation and combustion. They demonstrated that the higher the viscosity of a given oil, the larger the droplets. Moreover, for a given droplet size, vegetable oils evaporate less than heating oil at temperatures of below 500°C. Furthermore, combustion is significantly better for saturated vegetable oils such as palm or coconut than for unsaturated oils such as rapeseed, soybean or sunflower. Cottonseed oil, which was also used in the study, falls somewhere in between. As using these oils in engines did not produce the desired result, the researchers took the necessary steps to ensure that the oil droplets were the same size as fuel oil droplets. The result was almost instantaneous: once vegetable oils reach a temperature of 150°C, droplet size is the same as for fuel oil. The second stage was to control evaporation. Again, it is temperature (that of the environment in which evaporation takes place) that can be used to achieve the desired result. Provided that temperature exceeds 500°C, vegetable oil evaporation is similar to that of diesel.
The recipe obviously requires appropriate equipment, and thus means modifying engines and boilers in line with these usage parameters. A range of models has already been developed with the Italian manufacturer Riello. Tests conducted with an 80-kilowatt boiler have produced results similar to those of diesel engines, provided the temperature was sufficient for good combustion. Socfin, a rubber company, has already ordered such boilers for the driers at its plant in Ivory Coast. A boiler fuelled by palm oil was installed there in 2008. By the end of 2009, all the plant's boilers will have been replaced.
As regards polluting exhaust gas emissions, there is little difference between diesel and vegetable oils, except for fine particles. There are no regulations concerning fine particles as yet, but emissions from vegetable oils are 25% lower than from diesel, which is not to be sniffed at. Regulated emissions, carbon dioxide and nitrogen oxide (NOx), are equivalent to those of diesel, if not slightly lower.
Literature
Daho T., 2008. Contribution à l’étude des conditions optimales de combustion des huiles végétales dans les moteurs Diesel et les brûleurs : cas de l’huile de coton. Thesis, University of Ouagadougou.
Daho T., Vaitilingom G., Sanogo O., 2009. Optimization of the combustion of blends of diesel and cottonseed oil in a non-modified boiler. Fuel: doi:10.1016/j.fuel.2008.12.021
Vaitilingom G., 2006. Utilisations énergétiques de l’huile de coton. Cahiers Agriculture, 15 (1): 144-149.
- Category: Science