Sasongko, Mega Nur, and Widya Wijayanti. “Experiment Investigation on the Effect of Oxygen Percentage on Combustion Characteristics of Waste Cooking Oil Biodiesel”. International Journal of Integrated Engineering, vol. 13, no. 1, Jan. 2021, pp. 39-45, https://penerbit.uthm.edu.my/ojs/index.php/ijie/article/view/5554.