Eksperimentalno določanje termofizikalnih lastnosti motornih olj

Jug Blagovič, Žana (author), Karpe, Blaž (mentor)

V diplomskem delu so eksperimentalno določene in primerjane izbrane termofizikalne lastnosti dveh motornih olj proizvajalca MANNOL, ki sta se razlikovali v viskoznostnem razredu. Namen raziskave je ovrednotiti vpliv temperature in viskoznostnega razreda na gostoto, viskoznost in toplotno prevodnost motornih olj ter oceniti primernost izbranih merilnih metod za njihovo karakterizacijo. Preiskovani sta bili motorni olji MANNOL Longlife 504/507 5W-30 in MANNOL Classic 10W-40. Gostota je bila določena s piknometri, viskoznost s Höpplerjevim viskozimetrom s padajočo kroglico, toplotna prevodnost pa z metodo nestacionarnega ploščatega vira in metodo vroče žice. Meritve so bile izvedene v temperaturnem območju od sobne temperature do 90 °C. Z metodo nestacionarnega ploščatega vira so bili zanesljivi rezultati pridobljeni le pri sobni temperaturi. Pri 22 °C je bila povprečna toplotna prevodnost olja MANNOL Classic 10W-40 0,1726 W/(m·K), olja MANNOL Longlife 504/507 5W-30 pa 0,1501 W/(m·K). Pri višjih temperaturah so se pojavila velika odstopanja in nerealne vrednosti, zato temperaturne odvisnosti s to metodo ni bilo mogoče zanesljivo določiti. Pri metodi vroče žice je bilo ugotovljeno, da je izračunana toplotna prevodnost močno odvisna od načina določitve temperaturnega koeficienta električne upornosti senzorske žice. Razlike v toplotni prevodnosti glede na vrsto izračuna so se pri višjih temperaturah povečale in dosegle približno 18 % pri olju 10W-40 ter 14 % pri olju 5W-30. Ugotovljeno je bilo, da sta bila pri merjenju toplotne prevodnosti motornih olj ključna ustrezna omejitev vpliva konvekcije ter natančna temperaturna karakterizacija merilnega senzorja. Meritve gostote so pokazale, da se je gostota obeh motornih olj z naraščanjem temperature zmanjševala, pri čemer je imelo olje MANNOL Classic 10W-40 pri vseh primerljivih temperaturah višjo gostoto kot MANNOL Longlife 5W-30. Meritve s Höpplerjevim viskozimetrom so pokazale izrazito in nelinearno zmanjševanje dinamične in kinematične viskoznosti z naraščanjem temperature, pri čemer je olje 10W-40 v celotnem temperaturnem območju ohranilo višjo viskoznost od olja 5W-30.

• Language: Slovenian
• Keywords: motorna olja, termofizikalne lastnosti, toplotna prevodnost, viskoznost, gostota, nestacionarne merilne metode
• Work type: Bachelor thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2026
• PID: 20.500.12556/RUL-186186
• Publication date in RUL: 28.08.2026

Secondary language

• Language: English
• Title: Experimental determination of the thermophysicalproperties of engine oils

Abstract

The selected thermophysical properties of two MANNOL engine oils with different viscosity grades were experimentally determined and compared. The purpose of the study was to evaluate the influence of temperature and viscosity grade on the density, viscosity, and thermal conductivity of engine oils and to assess the suitability of the selected measurement methods for their characterization. MANNOL Longlife 504/507 5W-30 and MANNOL Classic 10W-40 engine oils were investigated. Density was determined by pycnometry, viscosity by a Höppler falling-ball viscometer, and thermal conductivity by the transient plane source method and the transient hot-wire method. Measurements were performed from room temperature to approximately 90 °C. Reliable results with the transient plane source method were obtained only at room temperature. At 22 °C, the average thermal conductivity was 0.1726 W/(m·K) for MANNOL Classic 10W-40 and 0.1501 W/(m·K) for MANNOL Longlife 504/507 5W-30. At higher temperatures, large deviations and unrealistic values occurred, so the temperature dependence could not be determined reliably using this method. With the transient hot-wire method, the calculated thermal conductivity was found to depend strongly on the procedure used to determine the temperature coefficient of electrical resistance of the sensor wire. The differences in thermal conductivity between the two calculation procedures increased at higher temperatures and reached approximately 18% for the 10W-40 oil and 14% for the 5W-30 oil. It was concluded that reliable thermal-conductivity measurements of engine oils required effective limitation of convection effects and accurate temperature characterization of the measuring sensor. Density measurements showed that the density of both engine oils decreased with increasing temperature, with MANNOL Classic 10W-40 exhibiting a higher density than MANNOL Longlife 5W-30 at all comparable temperatures. Measurements using the Höppler viscometer revealed a pronounced and nonlinear decrease in both dynamic and kinematic viscosity with increasing temperature, while the 10W-40 oil maintained a higher viscosity than the 5W-30 oil throughout the investigated temperature range.

• Keywords: engine oils, thermophysical properties, thermal conductivity, viscosity, density, transient measurement methods