Sustainability as it relates to Carbon dioxide emissions, friction and wear

Following the growing world population and demands of energy as well as amenities, many studies have proved the use of fossil-based fuels as the main contribution of climate change and global warming. The consequences are evident from rising temperatures, sea levels and an increase in the intensity and frequency of extreme weather conditions. Therefore, immediate actions, including limitations on CO2 and fine particulate emissions in internal combustion engines, need to be taken to reduce energy-consumption levels and pollution. Transportation, power generation and manufacturing are essential industrial activities in modern societies that will generate a great amount of carbon dioxide and greenhouse gases. These activities involve many different forms of machinery and mechanical systems with numerous moving parts and contacting surfaces [1]. Tribology is the science of interacting surfaces in relative motion under relative loads and encompasses the study of friction, wear, lubrication and related design aspects [2]. Smooth, reliable, and long-lasting operations of these machines heavily depend on how well friction and wear can be controlled in these systems [1].
Material efficiency and resource conservation can be achieved through products with a longer life cycle [1]. Since tribology has become a key factor in developing sustainable technologies, this contribution aims at exploring the global impact of tribology in terms of CO2 emissions.

Tribology has become a cross-sectional technology involving biology, chemistry, engineering, materials science and mathematics of economic importance. It combines economic aspects and sustainability in terms of correlating CO2 emissions and friction. As a result, tribology has both direct and indirect effects on certain global sustainable development goals (SDG) as outlined in Table 1 [3]. Table 1 emphasizes the tremendous impact tribology can make from energy efficiency through wear protection and lubrication. Wear protection and condition monitoring help to extend service life and functionality of components. Therefore, fewer replacement parts are required for production and handling operations, reducing overall materials, energy and work [3]. Another fundamental aspect of tribology is lubrication. Lubrication is essential for optimizing friction in sliding surfaces, minimizing direct surface contact, and reducing tool wear and power requirements. Lubricants consisting of base oils and additives synthesized from biomasses are the most suitable options, as they are made of renewable raw materials [3]. The tonnage of lubricants corresponds to about 1% of the fuel volume [3]. Moreover, there is enough biomass tonnage available to feed the synthesis of chemicals needed for formulating about 38-42 million metric tons of lubricants consumed annually.
Furthermore, the correlation between energy efficiency and CO2 emissions is evident in Figure 1, which shows the estimation of key scenarios for reducing CO2 emissions to limit global warming by 2oC in 2050. As opposed to carbon capture and storage and renewables, the largest impact is expected to come from end-use energy efficiency (38%), which includes energy generated in industry, services, agriculture and households. A 2017 analysis of earlier studies calculated that approximately 23% of the world’s total energy consumption is related to tribological contacts [1]. 20% is used to overcome friction and the remaining 3% is connected with remanufacturing worn parts and spare equipment due to wear and wear-related failures [1]. Assuming that friction losses can be reduced by 30-40%, the medium and long-term global savings potentials, the potential for reducing primary energy by reducing friction has a wide range of predictions: 8.6% (Holmberg, 2017) [1], 8% (Holmberg, 2019) [5], 10.9% (ASME, 1977) [6], 13% (US Congress, 2016) and 24% (ARPA-E, 2017) [7]. In consequence, based on 33.3 gigatons of CO2 emissions in 2017, about 2.66-4.93 gigatons of CO2 per year could be avoided by reasonable and appropriate measures to reduce friction and wear.
Thus, a large emphasis has been placed on tribological research. This progress includes the development of new materials and coatings, surface engineering (surface treatments, modifications and texturing), and lubricants and additives (nanomaterials and solid lubricants), as well as innovative technical solutions such as new component designs [8]. The coefficient of friction (COF) in the “milli-range” is en vogue in research and will greatly reduce CO2 emissions, if widely applied in practice. Some of the solutions for friction and wear reduction can be directly applied to existing machines, but some may only be compatible with newer or more advanced instruments [1]. Many industries also aim at synthesizing lubricants with the focus on biodegradable and eco-friendly characteristics [9].
Within the scientific community, there is an increased awareness of tribology and its impact on sustainability with more efforts into investigating this field. Table 2 shows the potential average friction and wear reduction rate in 2017 as well as levels estimated to be possible to achieve in 2030 [1,8]. These estimations are based on the average friction and wear levels of today’s devices compared to the relative friction and wear reduction in today’s new commercial devices, the lowest levels measured in research laboratories and the levels estimated to be possible to achieve up to 2030. This data focuses on the transport, energy, industrial and residential sectors.
Table 3 displays the estimated potential energy and savings and CO2 emissions reduction in some geographic regions in the long term (15 years), as a result of better tribological performance [1]. The figures are calculated as related to the total primary energy supply (TPES). Due to people’s improved understanding of tribology and its implementation, friction and wear reduction rates are expected to increase in the future (Table 2) and can ultimately improve cost and energy savings as well as CO2 emission reduction (Table 3).
In conclusion, following the population growth that leads to higher energy demand on a global scale, tribology plays a key role in reducing CO2 emissions related to energy-consumption levels. Tribology has both direct and indirect effects on various SDGs through energy efficiency, in terms of friction and wear protection. Hence, a lot of efforts must be undertaken to implement the pre-existing knowledge and develop new business models. However, it needs to be emphasized that sustainability is not limited to environmental friendliness. By taking advantage of new materials, lubrication technologies and condition monitoring in many machinery and other equipment, energy losses may be significantly reduced, which can be estimated to be about 3.1 gigatons of CO2 emissions or ~9% of the total direct CO2 emissions in 2017.

References:

[1] Holmberg K., Erdemir A, “Influence of tribology on global energy consumption, costs and emissions”, FRICTION, 2017; 5(3);264-284. Doi: 10.1007/s40544-017-0183-5.
[2] Jin Z., Fisher J., “Tribology in joint replacement”, Joint replacement technology, 2008
[3] Woydt M., Hosenfeldt T., Luther R., Scholz C., Bäse M., Wincierz C., Schulz J., “Wear protection and sustainability as cross-sectional challenges”, German Society for Tribology ( www.gft-ev.de ), 2021, https://www.gft-ev.de/en/tribology-in-germany-wear-protection-and-sustainability-as-cross-sectional-challenges/
[4] IEA Energy Technology Perspectives 2008, “Scenarios & Strategies to 2050”, IEA International Energy Agency, Paris, France 2010. ISBN 978-92-64-04143-1
[5] K. Holmberg and A. Erdemir, “The impact of tribology on energy use and CO2 emission globally and in combustion engine and electric cars.“, Tribology International, 2019, Vol. 135, pp. 389-396
[6] O. Pinkus and D.F. Wilcock, “Strategy for Energy Conservation through Tribology”, 1977, The American Society of Mechanical Engineers, New York, NY 10016-5990, USA; www.asme.org
[7] P.M. Lee and R. Carpick (eds.), Tribology Opportunities for Enhancing America´s Energy Efficiency – A report to the Advanced Research Projects Agency, 14th February 2017, U.S. DoE, https://alliance.seas.upenn.edu/~carpickg/dynamic/wordpress/wp-content/uploads/2012/03/TribologyARPAE_FINAL.pdf
[8] Holmberg K., Kivikytö-Reponen P., Härkisaari P., Valtonen K., Erdemir A. “Global energy consumption due to friction and wear in the mining industry”, Tribology International, 2017;116–139
[9] Saini V., “Aspects of green-sustainable tribology and its impacts on future product development: A Review”, Ecology, Environment and Conservation. 25, 2019;146-157
[10] Shah R., Woydt M., Huq N., Rosenkranz A., “Tribology meets sustainability”, Industrial Lubrication and Tribology, 2020, DOI: 10.1108/ILT-09-2020-0356