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In the present work the evaluation of coconut and palm oil as lubricants in four-stroke engine was carried out and the performance was compared with commercially available engine oil. The tribological properties of oil samples collected from the engine at regular interval were evaluated by means of four ball tester. The emissions from engine were monitored by using exhaust gas analyzer. It was observed that antiwear properties of fresh vegetable base oils and engine oil were comparable at ambient conditions. The observed deviation with usage was linked to the oxidation and the absence of additives in vegetable oil. The increased wear with commercial engine oil was due to depletion of additives. Increased fuel efficiency and reduction in the concentration of oxides of carbon and nitrogen in the emission observed with vegetable oil based lubricant was linked to its high flash point.

Vegetable oils are a potential source of base oils for biodegradable lubricants, with limited oxidative stability. This study focuses on the effect of long-term ageing and the infl uence of oxidation products on the boundary lubrication performance of coconut and soy bean oils, by subjecting them to accelerated ageing in a dark oven at elevated temperature. The samples were collected at regular intervals and analysed for the changes in viscosity, percentage of free fatty acid and peroxide number compared to fresh oil samples. The boundary lubrication properties of these samples were evaluated using a four-ball tester. Increased wear observed with aged oil samples was linked to the destruction of triglyceride structure and formation of peroxides. The difference in the wear properties of soy bean oil to coconut oil was accounted by its high content of unsaturated fatty acids and its susceptibility to undergo oxidation. It was concluded that the coconut oil can perform as a better lubricant and has got a better storage life compared to soy bean oil.

Increased demand to protect the environment from mineral oil based lubricants has necessitated replacing them with products derived from natural resources. In addition to this a combination of environmental, health, and economic challenges has also renewed interest in the development and use of green lubricants over the last two decades. This chapter gives an overview of green lubricants beginning from their ancient use to the challenges prospective of the lubricant industry. The review includes structural and chemical properties of important vegetable oils and chemical modification of vegetable oils. Tribological behavior of products based on vegetable oils, green additives, and ionic liquids under varied testing conditions is also presented. This study also gives an insight into the testing procedures and sustainability aspects of green lubricants and additives.