7Biodiesel, which comprises fatty acid esters, is derived from different sources, such as vegetable 8 oils from palm, sunflower, soybean, canola, jatropha, and cottonseed, animal fats, and waste 9 cooking oil. Biodiesel is considered as an alternative fuel for diesel engine. However, biodiesel 10 has poor cold flow behavior (i.e., high cloud point & pour point) and oxidation stability 11 compared with petroleum diesel because of the presence of saturated and unsaturated fatty acid 12 esters. Consequently, the performance of biodiesel during cold weather is affected. When 13 biodiesel is oxidized, the subsequent dregs can adversely affect the performance of the fuel 14 system as well as clog the fuel filter, fuel lines, and injector. This phenomenon results in start-up 15 and operability problems. Cold flow behavior is usually assessed through the pour point (PP), 16 cloud point (CP), and cold filter plugging point (CFPP). Earlier studies on cold flow focused on 17 reducing the devastating effect of poor cold flow problems, such as lowering the PP, CP, and 18 CFPP of biodiesel. This present paper provides an overview of the cold flow behavior and 19 oxidation stability of biodiesel, as well as their effect on the engine operation system. The 20 improvements on the behavior of cold flow of biodiesel are also discussed.21

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The increasing use of bioethanol causes tribological effects on engine components. It is crucial to study the effect of bioethanol on oil degradation and friction and wear behaviors of engine oil, using four-ball wear tester.