Ngamjaroen, S., W. Pakdee, and C. Pattamaprom. “The Effect of Storage Degradation of Palm- Stearin Biodiesel on Engine Performance and Exhaust Emission”. Science & Technology Asia, vol. 15, no. 5, Oct. 2015, pp. 32-38, https://ph02.tci-thaijo.org/index.php/SciTechAsia/article/view/41237.