{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,31]],"date-time":"2026-07-31T06:02:31Z","timestamp":1785477751255,"version":"3.56.0"},"reference-count":42,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2023,1,12]],"date-time":"2023-01-12T00:00:00Z","timestamp":1673481600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Ageing of engine oil is an important issue determining the engine life and performance. The present work attempts to delineate the ageing-induced changes in engine oil through the mode-mismatched dual-beam thermal lens (MMDBTL) technique and other conventional spectroscopic techniques. For the analyses, engine oil samples were collected after every 200 km of runtime. As the thermal diffusivity is related to the nonradiative deexcitation upon optical absorption, comprehensive radiative and nonradiative analyses were carried out. The Ultraviolet-Visible, Fourier transform infrared, and Nuclear magnetic resonance spectroscopic analyses point to the structural modification as a result of the breaking of the long-chain hydrocarbons into ketones, aldehydes, esters, and other compounds. This modifies the absorption pattern, which can also be understood from the nonlinear refractive index study using the Z-scan technique. The compositional variations associated with the degradation upon ageing, the length of the hydrocarbon chain, and the formation of newer molecules account for the enhancement of the thermal diffusivity revealed through the MMBDTL techniques. The complementary nature of the radiative and nonradiative emission is understood from the fluorescence study. Thus, the study reveals the possibility of thermal diffusivity measurement as an effective tool for the quality monitoring of engine oil.<\/jats:p>","DOI":"10.3390\/ma16020773","type":"journal-article","created":{"date-parts":[[2023,1,13]],"date-time":"2023-01-13T02:57:33Z","timestamp":1673578653000},"page":"773","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Reflecting the Quality Degradation of Engine Oil by the Thermal Diffusivity: Radiative and Nonradiative Analyses"],"prefix":"10.3390","volume":"16","author":[{"given":"Vijayakumar","family":"Gokul","sequence":"first","affiliation":[{"name":"Department of Optoelectronics, University of Kerala, Trivandrum 695581, Kerala, India"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5147-3172","authenticated-orcid":false,"given":"Mohanachandran Nair Sindhu","family":"Swapna","sequence":"additional","affiliation":[{"name":"Laboratory for Environmental and Life Science, University of Nova Gorica, Vipavska 13, SI-5000 Nova Gorica, Slovenia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dorota","family":"Korte","sequence":"additional","affiliation":[{"name":"Laboratory for Environmental and Life Science, University of Nova Gorica, Vipavska 13, SI-5000 Nova Gorica, Slovenia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sankaranarayana Iyer","family":"Sankararaman","sequence":"additional","affiliation":[{"name":"Department of Optoelectronics, University of Kerala, Trivandrum 695581, Kerala, India"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,1,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"27","DOI":"10.1016\/B978-012639855-7\/50041-7","article-title":"Environmental Aspect of Air Pollution","volume":"Volume 1","author":"Sher","year":"1998","journal-title":"Handbook of Air Pollution from Internal Combustion Engines\u2014Pollution Formation and Control"},{"key":"ref_2","first-page":"1","article-title":"Engine Exhaust Emissions","volume":"Volume 1","author":"Springer","year":"1973","journal-title":"Engine Emissions\u2014Pollutant Formation and Measurement"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"125869","DOI":"10.1016\/j.energy.2022.125869","article-title":"Performance Optimization of a Diesel Engine Fueled with Hydrogen\/Biodiesel with Water Addition Based on the Response Surface Methodology","volume":"263","author":"Tan","year":"2023","journal-title":"Energy"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Nikolakopoulos, P.G., Mavroudis, S., and Zavos, A. 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