Biodiesel production from algae oil and its use in a diesel engine as alternati̇ve fuel

In this study, biodiesel production from algae oil via transesterification reaction and its use in diesel engines were investigated. To produce biodiesel, oil, obtained from single-cell and heterotrophic Chlorella protothecoides algae species adapted for oil production and grown in fresh water in which 5% thermal water is added and in which there is closed-loop full-automatic pyramid photo bioreactors, was used; and base-catalyzed transesterification was applied due to its low acid value. Methyl alcohol and potassium hydroxide (KOH) with purities of 98% and 99.9%, respectively, were used for transesterification of algae oil. A series of lab-scale preliminary experiments were carried out to determine the optimal transesterification conditions. In these experiments, molar ratio of methanol to oil was kept as 6:1 and the effects of the amount of catalyst (%0.5, %0.75 and %1 KOH of the oil by wt.), reaction temperature (60-70 oC) and time (60-100 minutes) on the methyl ester yield, kinematic viscosity and density values were studied. Consequently, the molar ratio of methanol to oil of 6:1, in the presence of 0.75 wt.% KOH of the oil as catalyst at 68 °C for 80 minutes, was agreed as the optimal transesterification conditions for producing algae oil methyl ester (biodiesel). Under these conditions, a 98.6% conversion rate of algae oil to fatty acid methyl esters efficiency was achieved, and kinematic viscosity and density of final biodiesel product were measured as 4.491 mm2/s and 881 kg/m3, respectively. According to phsico-chemical analyses of biodiesel produced, it was determined that it had an ester content higher than 96%, and the contents of methanol, mono-, di-, tri-glyceride and free and total glycerin were found to be below the limits specified by ASTM D6751 and EN 14214 standards. It was also found that fuel properties such as kinematic viscosity, density, flash point, cetane number, acid value, sulphur and water content agreed well with the standards. Furthermore, the fact that the biodiesel had a high cetane number (57.3) and low CFPP (-10 0C) besides standard fuel properties makes it a suitable alternative diesel fuel. The biodiesel and its blend with petroleum based diesel fuel in percentage of 20% (v/v) were tested in four-cylinder and direct injection diesel engine at constant engine speed and variable load conditions to assess the combustion, performance and exhaust emissions in comparison with petroleum based diesel fuel. From the experimental test results, it was observed that using biodiesel and blended fuel as fuel instead of petroleum diesel resulted in an increase in specific fuel consumption and in a slight reduction in efficiency. Also, a slightly higher peak cylinder pressure and heat release rate were obtained by using biodiesel and blended fuel in comparison with petroleum diesel. The results of exhaust emission tests showed the sharp reductions in total hydrocarbon emissions and smoke opacity, despite increasing in NOx emissions.