Unsteady Heat Conduction Phenomena in Internal Combustion Engine Chamber and Exhaust Manifold Surfaces

Abstract

Heat transfer to the combustion chamber walls of internal combustion engines is recognized as one of the most important factors having a great influence both in engine design and operation (Annand, 1963; Assanis & Heywood, 1986; Heywood, 1988; Rakopoulos et al., 2004). Research efforts concerning conduction heat transfer in reciprocating internal combustion engines are aiming, among other, to the investigation of thermal loading at critical combustion chamber components (Keribar & Morel, 1987; Rakopoulos & Mavropoulos, 1996) with the target to improve their structural integrity and increase their factor of safety against fatigue phenomena. The application of ceramic materials in low heat rejection (LHR) engines (Rakopoulos & Mavropoulos, 1999) is also among the large amount of examples where engine conduction heat transfer is a dominant factor. At the same time, special engine cases like the air-cooled (Perez-Blanco, 2004; Wu et al., 2008) or HCCI ones demand a special treatment for a successful description of the heat transfer phenomena involved. Today, technology changes in the field of the internal combustion engines (mainly the diesel ones) are happening extremely fast. New demands are added towards the areas of controlled ignition of new and alternative fuels (Demuynck et al., 2009), reduction of tailpipe emissions (Rakopoulos & Hountalas, 1998) and improved engine construction that would ensure operation under extreme combustion chamber pressures (well above 200 bar). However, application of these revolutionary technologies creates several functional and construction problems and engine heat transfer is holding a significant share among them. Engine heat transfer phenomena are unsteady (transient), three-dimensional, and subject to rapid swings in cylinder gas pressure and temperatures (Mavropoulos et al., 2008), while the combustion chamber itself with its moving boundaries adds further to this complexity. In modern downsized diesel engines, the extreme combustion pressure and temperature values combined with increased speed values lead to increased amplitude of temperature oscillations and thus to enormous thermal loading of chamber surfaces (Rakopoulos et al., 1998). At the same time, transient engine operation (changes of speed and/or load) imposes a significant additional influence to the system heat transfer, which cannot (and should not)