Experimental and theoretical study of the short term response temperature transients in the cylinder walls of a diesel engine at various operating conditions

The present work concerns a combined experimental and theoretical investigation of the interesting phenomenon of short term response (cyclic) temperature transients in the combustion chamber walls of a reciprocating internal combustion engine. The experimental work is carried out on a direct injection (DI), air-cooled, four-stroke, diesel engine located at the authors' laboratory. For this purpose, a novel experimental installation has been developed, which uses a new pre-amplification unit for the in-house developed fast response wall thermocouples and an object-oriented control code for fast data acquisition. A comprehensive simulation code of the thermodynamic cycle of the engine is developed, taking into account both the closed and the open parts of it. For the closed part, thermodynamic analysis of the measured pressure indicator diagrams is carried out to yield local temperature histories and the fuel burned mass rate, after combining it with a gas heat transfer sub-model. For the open part, a purely theoretical thermodynamic analysis is developed, applying the energy and state equations with appropriate gas heat transfer and mass exchange with the atmosphere sub-models. The model is appropriately coupled to a wall periodic conduction model, which uses as boundary condition the gas temperature variation throughout the engine cycle after being treated by Fourier analysis techniques. The theoretical analysis results compare well with the corresponding experimental ones, at the load and speed conditions examined. The influence that engine operating conditions and wall material properties have on the values of cyclic temperature swings is demonstrated. These oscillations, apart from possibly impairing the engine performance, may take prohibitive values due to high wall thermal fatigue, when materials such as thermal insulators are used. (C) 2003 Elsevier Ltd. All rights reserved.