Hayat, N., H. U. Mughal, H. Z. Nabiand, and G. Moeenuddin. “Impact of Natural Gas and Biogas on Engine Lube Oil Condition”. The Nucleus, vol. 54, no. 2, June 2017, pp. 83-89, http://202.83.167.189/index.php/Nucleus/article/view/58.