Assessment of tree seed oil biodiesel: A comparative review based on biodiesel of a locally available tree seed

The present investigation is undertaken to investigate prospect of seeds of a locally available tree (koroch) for biodiesel production. The middle-size, evergreen koroch tree with spreading branches are available in Assam. The characteristics of koroch biodiesel and engine performance fueled by koroch biodiesel are also analyzed reviewing similar results available in the literature so as to ascertain its status. Twelve number of different tree seed oils, reported earlier, are considered for making the present comparative assessment. Though transesterification has been the common process for converting tree seed oil into biodiesel, as evidenced from the literature consulted in this study, but there have been variations of the chemical processes. Variations of the transesterification are attributed to (i) types of catalysis viz., acid (H₂SO₄) or base (KOH, NaOH, and NaOCH₃), (ii) reaction temperature, (iii) molar ratio, (iv) nature of reaction viz., single stage or multi-stage. The outputs of the reaction have also been found varying in terms of yield as well as quality. Quality of biodiesel, however, was found to influence by the nature of feedstock. The assessment of quality parameters was made either by ASTM D 6751 or EN 14214 standards. The major fuel properties such as calorific value, kinematic viscosity, cetane number and cloud point of the reference biodiesel (koroch biodiesel) are compared with the properties of five biodiesel obtained from non-edible tree seed (karanja, mahua, polonga, jatropha and rubber seed) and then ranked them in order of desirable property. No single biodiesel type could be found at top rank with reference to more than one property. With regards to viscosity, except rubber seed biodiesel, all other biodiesels (karanja, mahua, polonga, jatropha and koroch) fulfilled the ASTM D 6751 (1.9-6 cSt) as well as EN14214 (3.5-5) standards. Koroch biodiesel ranks 3rd, 3rd and 6th in case of kinematic viscosity, cetane number and calorific value amongst the biodiesel types considered for the present study. Cloud point of koroch, polanga, mahua, rubber, karanja and jatropha biodiesels are 4, 13.2, 5, 4, 12 and 4 °C. Further, properties of biodiesel were found to have influencing correlation with the fatty acid characteristics of the feedstock. Therefore, biodiesel with desirable properties could be expected form optimum mixing of different feedstock.Eleven number of different engine performance results pertaining to uses of biodiesel are also reviewed in this paper. Varying test conditions with reference to fuel types and blends, engine size and loading pattern are discussed. Engine performance results of koroch biodiesel were then compared with five similar tree-based biodiesel. It is observed that tree seed oil with more unsaturated fatty acids exhibits lower thermal efficiency compared to biodiesel having more saturated acids.