Influence of engine oils dilution by fuels on their viscosity, flash point and fire point

Abstract

U sklopu ovog rada ispitivan je utjecaj razrjeđenja automobilskih sintetičkih i mineralnih motornih ulja dvjema vrstama komercijalnih goriva: motornim benzinom – Eurosuperom 95 i dizelskim gorivom – Eurodizelom. Time se simulirao slučaj koji se može dogoditi u motoru – prolazak neizgorena goriva u kućište motora te miješanje i otapanje u motornom ulju. Kao najvažniji parametri za praćenje promjena karakteristika ulja odabrani su viskoznost, plamište i gorište. Razrjeđenje ulja gorivom kretalo se u rasponu od 0% do 10% masenoga udjela (wt) goriva. Uzorci motornih ulja koji su korišteni u ispitivanjima nabavljeni su od dvaju proizvođača prisutnih na hrvatskom tržištu, po jedno čisto mineralno i jedno potpuno sintetičko multigradno motorno ulje gradacija viskoznosti prema SAE gradaciji: 15W-40 i 5W-30, bez dodatnih modifikacija. Promjene svojstava ulja premašile su pretpostavljene praktične vrijednosti potrebne za siguran rad motora u slučaju razrjeđenja ulja s benzinom u iznosu od 10 wt%. Razrjeđenje ulja sa 5 wt% benzina je maksimalni iznos uz koji se može očekivati mogućnost njegove praktične primjene za podmazivanje motora jer se plamište ispitivanih ulja snižava na temperature koje se već javljaju u primjeni – oko 150 °C ili niže. Kada se ulja razrijede dizelskim gorivom, tada se praćena svojstva ulja mijenjaju manje nego što je to slučaj s benzinom.In this project the influence of dilution of synthetic and mineral engine oils with two commercial fuels – gasoline (type Eurosuper 95) and diesel fuel (type eurodiesel) was studied. The situation that could really occur in the automotive engine was simulated – a breakthrough of unburned fuel to engine oil and its mixing and dissolution. Viscosity, fire point and flash point were chosen as the most important parameters to follow the changes in oil-fuel mixtures. The dilution range was between 0 and 10 wt% of fuel in the oil-fuel mixture. The samples used in this investigation were bought directly from the two producers present on the Croatian market, without further modification. The samples were multigrade mineral and synthetic oils – mineral oil with SAE gradation 15W-40 and synthetic oil with SAE gradation 5W-30. The changes of oil properties were too high for assumed safe use in engines in the case of oil dilution with 10 wt% of gasoline. The dilution of oil with 5 wt% of gasoline was maximal level of dilution that could be expected to be still adequate for use in engines, because the flash points of these mixtures were mostly near 150 °C, which is assumed as maximal allowed working temperature of engine oil. The properties of mixtures of the same oils with diesel fuel showed smaller changes than mixtures with gasoline