## 1 Introduction  
Biomass fast pyrolysis fuel is a renewable, environmentally friendly, and biodegradable fuel alternative that has attracted significant attention. This type of crude oil is produced through the fast thermal pyrolysis of biomass materials such as rice husks [1]. Using biofuel reduces vehicle emissions and subsequently improves fuel efficiency [2; 3; 4; 5; 6; 7]. However, biomass crude fuels cannot be used directly in diesel engines because of their high water content, low thermal value, and high acidity. Emulsified biomass crude fuel and refined biomass fuel are the most efficient types of biomass fuel [8]. Regarding the use of emulsified biomass fuels in diesel engines, we should consider the effects of biofuel on the lubricating oil. The tribological properties of biofuels have been studied extensively. [PERSON] [9] affirmed that the waste derived from intermediate pyrolysis oils has better lubrication but could corrode certain parts of the engine. [PERSON] [10] described the components of biomass crude oil, and the wear and friction mechanisms of biomass fuels were attributed to the organic chemical reaction of film formation on the friction pair under boundary lubrication conditions. The increase in wear during the rubbing process also increased the temperature, which resulted in corrosion. [PERSON] [11] determined the tribological performances of biomass crude oil and refined biomass oil by using a four-ball tribometer and a high-frequency reciprocating test rig. The biomass crude oil lubricated better than the refined biomass oil because of the reduction in long-chain organic matter in the latter. The anti-friction properties of biomass fuels were better than those of diesel fuels. However, the anti-wear and anti-corrosion properties of biomass fuels were worse than those of diesel fuels. The effects of these fuels on the tribological performance of engine oils have been examined. [PERSON] [12] investigated how various percentages of palm oil diesel (POD)-contaminated lubricants affect the wear behaviour of cast irons during sliding contact. A low percentage of POD (preferably 5% by weight) contamination functioned as an anti-wear additive that improved the performance of the lubricant on cast iron. [PERSON] [13] investigated the contamination of a lubricant with POD and the effects of a surface-hardening treatment on the wear and friction of AISI 1045 steel. Corrosive wears and pits were found on the specimen's surface when plain biofuel was used as a lubricant. This finding confirmed that the surface-hardened steel specimen had better wear resistance with a 4% biofuel-contaminated lubricant. [PERSON] [14; 15] reported that rapeseed-oil-based bio-lubricant and biodiesel-contaminated synthetic lubricant had better wear resistance and friction mitigation than the synthetic lubricant alone under similar operating conditions. Thus, long-term use of the newly formulated bio-lubricant and biodiesel might have a positive effect on engine life. The emulsified biomass fuel had no observable effects on the tribological behaviour of the engine lubricating oil between the cylinder liner and the piston ring friction pair. Heavy-duty diesel is usually used in marine or tractor diesel engines, which are less fastidious than other diesel engines regarding lubricating oil. On the other hand, it is a little difficult to directly use biomass fuel in normal diesel engines because of the complex composition of biomass fast pyrolysis fuels. The successful use of biomass diesel will depend on solutions to many problems. One of aspects that should be focused on is the fuel's dilution of the lubricating oil in the engine, and we did exactly that in the present research. Thus, we studied the effects of the emulsified biomass fuel contents on the tribological performance of a fully formulated engine oil (FFEO, CD SAE 15W-40) in simulations of engine cylinder liners and piston rings.