International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231
New generation of nanolubricants fuel economy
125
2022
Marta Hernaiz
Iker Elexpe
Esibaliz Aranzabe
Tomas Pérez Gutierrez
Beatriz Dominguez
ict2310141
23rd International Colloquium Tribology - January 2022 141 New generation of nanolubricants fuel economy Marta Hernaiz TEKNIKER research centre, Eibar, Spain Corresponding author: marta.hernaiz@tekniker.es Iker Elexpe TEKNIKER research centre, Eibar, Spain Estibaliz Aranzabe TEKNIKER research centre, Eibar, Spain Tomas Pérez Gutierrez REPSOL Technological centre, Madrid, Spain Beatriz Dominguez REPSOL Technological centre, Madrid, Spain 1. Introduction Climate change is one of the greatest challenges of our era, however, the need to ensure access to energy to ensure quality of life and economic development is just as important. The Sustainable Development Goals (2015-2030) [1], are a United Nations-driven initiative to continue the development agenda; through Climate Action Goal, calls for urgent action to address climate change and its effects; the figures to be faced such as the 50% increase in CO 2 emissions since 1990; and the increase in emissions between 2000-2010 is higher than in the previous three decades, highlights the need to define the necessary measures to meet responsibilities and facilitate a prosperous, supportive and compatible future with climate security and the limits of the planet. The need to reduce emissions does not exclude the use of fossil fuels but requires a significant change of direction; the transition to a sustainable energy system offers the opportunity to improve energy efficiency from source to use ensuring better quality of life and economic growth, while reducing the environmental footprint of the energy sector. Fuel Economy lubricants are the alternative to meet EU requirements to reduce fuel consumption while maintaining engine protection performance. Lubricant manufacturers are facing a new challenge and need to explore new technologies. The use of nanotechnology and nanomaterials (NM), (one or more external dimensions is in the size range 1-100 nm.) [2] offers a new range of lubricants and in recent years the number of studies on the potential of nanomaterials to improve the performance of lubricants is increasing [3]. The limited information available on long-term systems and the evolution of the properties and performance achieved with the dispersion of nanomaterials shows that currently the biggest challenge for nanofluids in general, and nanolubricants in particular, is the challenge of long-term stabilisation, and this property is what limits the market penetration of this type of product. The most common stabilisation strategy for NMs in a fluid is the use of surfactants that induce steric and electrostatic stabilisation on the NM, although this route, despite its advantages such as cost and simplicity of preparation, generates nanofluids with limited stability over time, which makes it not the most appropriate strategy. In this work we present the surface functionalisation of a nanomaterial as a dispersion strategy to obtain a stable and functional system over time. The physical anchoring of a chemical compound on the surface of the NM seeks to cover several objectives, on the one hand to ensure maximum compatibility between NP/ fluid, on the other hand to maintain the properties inferred to the lubricant over time, for this it is necessary to maintain the cluster size distribution. 2. Nanoparticle surface functionalization A metal oxide nanoparticle of 50nm has been surface functionalised through an esterification reaction with a fatty acid. The fatty acid due to its polarity will increase the stability of the NM in the fluid once it is dispersed, in the esterification reaction between the carboxyl group (COO-) of the fatty acid and the surface hydroxyl group (OH-) of the NM; the polar head is oriented towards the nanoparticle and the aliphatic chain (apolar) is oriented towards the oil stabilising the NM in the lubricant. 142 23rd International Colloquium Tribology - January 2022 New generation of nanolubricants fuel economy Figure 1: NM Surface functionalization Nanoparticle surface functionalization has been optimized via two main characterization techniques; infrared spectroscopy (FTIR) to identify determinate chemical bonds that prove the existence of covalent bonding between MO surface and carboxylate group of fatty acid, and thermogravimetric (TGA) technique to determine organic content in the NP surface. Figure 2: CH 2 bond symmetric & asymmetric at 2800cm -1 and COO bond of carbonyl at 1650cm -1 As Figure 2 shows spectroscopic analysis by FTIR evidence the characteristic peaks of fatty acid onto nanoparticle surface as reported by Suhaib [4]. Organic content in NP surface determined by TGA suggest a deposition of 80% in mass of fatty acid onto MO surface (Figure 3). Figure 3: TGA test of Np and functionalised NP 3. Nanolubricant formulation and performance characterisation Obtained functionalized nanomaterials have been dispersed in a PAO based fully formulated lubricant at different loads (0.2%, 05% 1% wt). Dispersion strategy of NP has been assisted by mechanical stirring assisted by ultrasonication device for 5min. Following figure show the aspect of nanolubricants once prepared and after 30 days of storage. As the photo shows the dispersion of functionalized nanoparticles not only improve nanofluid long-term stability also the colour and visual aspect of nanolubricant have been not affected, and this is an important property in lubricants and not reported in previous studies. Figure 4: Aspect and stability of formulated nanolubricants The tribological performance has been measured using a ball-on-disk tribometer (SRV) with a contact pressure up to 1.3GPa, 10mm/ s and at 80ºC. The friction coefficient (COF) and wear scar results expressed as percentage reduction for each system are plotted graphically. As can be seen, the use of functionalised NMs reduces both parameters and although the higher the concentration of NMs the greater the reduction in terms of COF, 1%wt has been considered as the optimum concentration, as a balance between tribological performance and NP load, reaching up to a reduction of 12% in COF and more than 5% in ball wear scar. Figure 5: Experimental results of SRV tribological test of nanolubricants 4. Nanolubricant characterisation Selected nanolubricants with 1% of functionalized metal oxide as functional additive has been characterized to determine other important physic parameters, such us viscosity (@40ºC and 100ºC), viscosity index, termoxidative stability by HPDCS (OIT in min) and cooling 23rd International Colloquium Tribology - January 2022 143 New generation of nanolubricants fuel economy properties expressed as overall heat transfer coefficient (h). Following table summarised experimental results. Table 1: Summary of main physic and thermal nanolubricant properties Property Reference PAO OIL 1.0% F-MO % variation D0.5 190nm OIT (min) by HPDSC 49,33 59,09 +20 h [KW/ m 2 K]*ɸ 40ºC 78,696 80,914 +2,82 h [KW/ m 2 K]*ɸ 100ºC 207,299 215,440 +3,93 IV 194 207 +6.7 Viscosity 40ºC 0.1577 0.1350 Viscosity 100ºC 0.0211 0.0214 5. Conclusion In this study the nanolubricant formulation by dispersion of surface modified metal oxide nanoparticle has been evaluated with the main objective to obtain nanolubricants with improved tribological performance, with long term stability and without modified aspect and colour of reference fluid, important but not reported property in lubricants. Proposed esterification route evidence effective chemical anchorage of fatty acid into NP surface evaluated by FTIR spectroscopy. By TGA the fatty acid content in the NP surface has been quantified reaching up to 80% of organic load. Performance, evaluated by tribological test, and main physic-chemical parameters, have shown that proposed strategy not only improve friction coefficient and antiwear properties of lubricant, also cooling properties and viscosity index have been booster without limit thermooxidative behaviour. The NM stability resilience and the good visual aspect of the obtained nanolubricant suggest exceptional potential as a new fuel economy nanolubricant. References [1] The 2030 agenda for sustainable development. United Nations. sustainabledevelopment.un.org [2] Recommendation on the definition of a nanomaterial 2011/ 696/ EU. [3] R.Saidur, K.Y.Leong, H.A.Mohammed. “A review on applications and challenges of nanofluids”. Renewable and Sustainable Energy Reviews. Volume 15, Issue 3, April 2011, Pages 1646-1668. [4] S.U. Ilyas, M. Narahari, J.T.Y. Theng, et al., “Experimental evaluation of dispersion behavior, rheology and thermal analysis of functionalized zinc oxideparaffin oil nanofluids”, Journal of Molecular Liquids (2019).
