**Abstract**

The scientific literature allows us to demonstrate the characteristics of high lubricity of biodiesel (particularly B100 from palm), which as a bio-fuel, can fulfill the function of bio-lubricant (B100 = 3 Ester); even surpassing motor oils in some respects (Synthetic Base = 2 Ester). Once its characteristics have been reviewed, we can affirm that it is possible to use B100 as a Bio-Lubricant in Diesel internal combustion engines, but also in spark-ignition engines. A comparison is made between commercial synthetic esters and fatty acid methyl esters ("FAME") designated B100. In the same context, we describe a procedure and a device designed to use B100 in diesel engines, not only as Bio-Fuel, but also as Bio-Lubricant, for both functions, successively and simultaneously, called "Bio-Circular Engine"; so: in Stage 1; biodiesel is taken from the fuel tank (B100) to the engine crankcase (previously filtered), where it will fulfill its first function as Bio-Lubricant. In Stage 2; the same B100 is conducted from the same crankcase to the fuel injection system (previously filtered and, if required, cooled) to fulfill the second function of Bio-Fuel. The "Bio-Circular Engine" is "Circular Economy", because it uses a single substance (B100), for two different and simultaneous functions (as Bio-Fuel and as Bio-Lubricant).

**Keywords:** biolubricant, esters, synthetic esters, lubricity, B100, diesel engine, internal combustion engine, B100 double function, bio-Circular engine
