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| Author(s): |
Roberto Balarini Junior
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2022-06-24 |
| Examining board members: |
Roberto Martins de Souza;
Marcio Gustavo di Vernieri Cuppari;
Henara Lillian Costa Murray;
Francisco José Profito;
Andre Zuin
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| Advisor: | Roberto Martins de Souza |
| Abstract | |
Despite extensive research into alternative methods, the internal combustion engine (ICE) is expected to remain as the main vehicular propulsion source in the next decades. Higher efficiency solutions are the main driving force for the future of ICE, being the use of renewable fuels, downsizing, low-viscosity engine oils and new additive packages, some of the most promising routes in this direction. Engine oil is a complex substance in its own, consisting of a base oil and various additives. Organic compounds based on molybdenum, such as molybdenum dithiocarbamate (MoDTC), are widely used as friction modifiers (FM) additives intended for the friction reduction , while the zinc dialkyldithiphosphates (ZDDP) is the antiwear (AW) additive most used in engine oils. In this scenario, the expansion of the use of ethanol as fuel has generated many investigations about its impact on the functionality of the oil additives. In general, due to the high evaporation latent heat of ethanol, lubricant contamination can be significant. Consequently, the contamination may affect the activation and formation steps of tribofilms formed from oil additives, which impacts on the final ICE efficiency. Consequently, loss of efficiency, excessive fuel consumption, higher emissions of pollutants and premature wear can be induced to the ICE. Therefore, this work has the objective of investigating the mechanical properties of the tribofilms formed from ZDDP and MoDTC in engines that run with anhydrous ethanol (AE). Thus, tribological tests were conducted in an SRV-4 tribometer (Optimol Instruments), with the tribological configuration of flat engine ring against AISI H13 steel plate, under reciprocating motion and lubricated contact. Three lubricating oils were tested, (i) PM (PAO 8 + 0.06 wt.% MoDTC); (ii) PMZ (PAO 8 + 0,06 wt.% MoDTC + 1% wt.% ZDDP), and (iii) FF (SAE 0W-20 fully-formulated engine oil), under new (fresh lube) and contaminated (with 10 wt% of AE) conditions. Results were evaluated in terms of friction, wear and tribofilms formed on the worn tracks. The tribolayers were identified by Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDX) and Raman Spectroscopy and, then, characterized by Atomic Force Microscopy (AFM) and Nanoindentation technique. The FF oil resulted in the lowest values of friction coefficient ( ~ 0.08), presenting the same range of values for fresh and contaminated conditions. The PM oil provided lower levels of friction for the fresh lubricant in relation to the contaminated condition ( ~ 0.10 versus ~ 0.16, respectively), which was also observed for the tests performed with PMZ lubricant ( ~ 0.09 and 0.12, respectively). The MoDTC activation was impaired by the AE addition to PM lubricant, resulting in tribofilm thickness reduction, whereas this effect was not noticed for FF and PMZ oils. The AE contamination induced higher levels of wear, especially in tests conducted with PM oil. The MoDTC tribofilm presented a highly plastic mechanical behavior, with hardness (H) and reduced elastic modulus (Er) of the order of 0.08 GPa and 8 GPa, respectively. On the other hand, the tribofilm formed with the PMZ and FF oils had higher mechanical properties, with H and Er measured values of approximately 4-5 and 140-160 GPa, respectively. For the lubricant under contamination condition, there is a trend to increase the hardness values of the resultant tribofilm, specially in terms of elastic modulus. (AU) | |
| FAPESP's process: | 17/19147-2 - Mechanical behavior of tribofilms formed from MoDTC and ZDDP additives in ethanol engines |
| Grantee: | Roberto Balarini Junior |
| Support Opportunities: | Scholarships in Brazil - Doctorate |