Changes in Total Friction in the Engine, Friction in Timing Chain Transmissions and Engine Emissions Due to Adding TiO2 Nanoparticles to Engine Oil
Authors: Wozniak M. , Batory D. , Siczek K. , Ozuna G. 
Published: August 2020

The main aim of the study was to evaluate changes in total friction in the engine, friction in its timing chain transmissions and engine emissions resulting from adding TiO2 nanoparticles to engine oil. The applicable engine oils and factors affecting their features were discussed. The drive from the crankshaft to the camshaft in an internal combustion engine is usually carried out by means of a cogged belt transmission or a chain transmission when high mileage is required without service operations. The engine performance of analyzed SI engine was obtained from the literature. The dependency of engine emission on engine operating speed was obtained using data from tests of a very similar engine under standard test conditions described in the literature. The changes in engine characteristics caused by varying internal friction conditions were estimated using the engine performance characteristic and engine friction losses, particularly in valve train chain transmission. The friction in such a chain transmission operating under oil lubrication conditions can be determined using its analytical model and measured friction torque occurring between the chain rollers and the pins. The analytical model was developed using the finite element method and additional mathematical formulas. The proposed model allowed obtaining weight and mass inertial moments of all valve train transmission components. The friction torque in contact zone chain roller–pin was obtained using the elaborated physical pendulum method for different conditions of lubrication, namely, without oil, with pure engine oil, and with engine oil containing TiO2 nanoparticles. The engine oil SAE 10W-40 with/without dispersed 2% wt. TiO2 nanoparticles was used during tests. The preparation process of studied oils was described. The resulted values of the friction torque in the chain transmission operating in different conditions of lubrication and changes in engine emission have been presented for tests before and after addition of TiO2 nanoparticles into engine oil. During the measurements it was observed that the addition of 2% TiO2 nanoparticles into engine oil reduced the total friction losses by 7–7.7%. Additionally, it was demonstrated that the timing drive and valve train generate about 14.4–18% of overall engine friction losses. Based on the results obtained from a comparative analysis of emission in the other engine with similar power characteristics, the mentioned total friction losses can change the emission of the following compounds in the analyzed SI engine: 17–19% for CO, 8–9% for CO2, 13–17% for NOx, and 12–16% for HC. Such changes were dependent on the engine speed. The smallest changes in engine were registered for the rotation speed of 2500 rpm. The oil consumption in the engine and its impact on the PM emission was estimated. The additional arrangements facilitating the extrapolation of the obtained friction results to the cases of using other oils and the method of measuring the PM emission on the test stand were proposed.