Heat transfer characteristics of some oils used for engine cooling Hosny Z. Abou-Ziyan * Mech. Power Eng. Dept., Faculty of Engineering, Mattaria, Helwan University, Cairo 11718, Egypt Received 1 July 2003; accepted 14 October 2003 Available online 13 April 2004 Abstract This paper reports the results of an experimental investigation of heat transfer from a cast iron test specimen to engine oils under boiling conditions. The work is aimed at evaluating the thermal character- istics of some engine oils in contact with high temperature parts in internal combustion engines. Three mono-grade oils and two multi-grade oils are examined at heat fluxes from about 30 to more than 400 kW/ m 2 for bulk temperatures of 40, 60, 80, 100, 125, 150 and 175 °C. The considered oils are analyzed and tested according to some ASTM standards to determine their additives concentration and to obtain some of their thermophysical properties. The results indicated that oil additives, oil properties and bulk temperatures have substantial effects on the oil characteristics. The boiling heat flux, for the best oil, rises by a factor of 1.65 as the bulk temperature decreases from 175 to 40 °C. The mono-grade oils produce superior heat transfer characteristics compared to those produced by multi-grade oils. The oil with the best additive concentrations produces boiling heat fluxes up to 4.44 times higher than those produced by some other oils. Comparing the results of the tested oils revealed that the oil that has the largest concentrations of boron, magnesium, phosphorus and zinc with low concentration of calcium yields the best heat transport characteristics among the other tested oils. These additives provide superior detergent and dispersant characteristics, reflected in the large alkalinity and low corrosivity of the oil. On the other side, calcium has a negative interaction with other additives and yields an adverse effect on heat transfer characteristics even when it exists in oil with large concentrations of boron, magnesium, phosphorus and zinc. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Engine cooling; Engine oil; Oil additives; Subcooled boiling Energy Conversion and Management 45 (2004) 2553–2569 www.elsevier.com/locate/enconman * Present address: State of Kuwait, P.O. Box 789, Surra 45708, Kuwait. Tel.: +20-9655347098; fax: +20-9654811753. E-mail address: hosnyaz@hotmail.com (H.Z. Abou-Ziyan). 0196-8904/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2003.10.005