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

In book: Heat Transfer - Engineering Applications
Source: InTech
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    ABSTRACT: The present work describes the development of a model for the calculation of the temperature field and heat flow in the combustion chamber components of internal combustion piston engines, which occur both under steady and transient engine operating conditions. Two and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner and cylinder head). The model is applied for the piston and liner of a medium speed diesel engine, for which relevant experimental data exist in the literature. Special care is given for accurately specifying the thermal boundary conditions (temperatures and heat transfer coefficients). Gas side boundary conditions are calculated using a thermodynamic cycle simulation code, including spatial variation of the gas side heat transfer coefficient. Coolant sides (water on the external liner surface and oil on the piston undercrown surface) boundary conditions are calculated using correlations pertaining to real engine conditions. Also an effort is made to model the piston-ring belt-liner complex thermal paths using equivalent thermal circuits. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements, revealing that the finite-element methods presented are successful in formulating this kind of problem, giving accurate results with reasonable computational cost. The utilization of the model reveals very clearly the essential role of engine operating transients (sudden changes in speed and/or load) in the generation of sharp temperature excursions in the metal components until a new steady state is reached. The phenomenon should be taken into account for correct engine design and safe operation (i.e. the avoidance of high local stresses).
    International Journal of Energy Research 01/1996; 20(5):437 - 464. DOI:10.1002/(SICI)1099-114X(199605)20:5<437::AID-ER169>3.0.CO;2-J · 2.74 Impact Factor
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    ABSTRACT: A new hybrid finite-element thermostructural model is developed and applied for the investigation of the thermal effects of various insulation configurations on the combustion chamber surfaces of a DI (direct injection) diesel engine, under transient operating conditions. The model uses a comprehensive thermodynamic engine cycle simulation model in combination with a detailed structural analysis model, which allows the study of the effect of engine geometry and construction parameters on its performance. The separate representation of the various component subregions by the hybrid model makes possible the quantitative estimation of the effect of contact resistances on the amount of heat rejected to the combustion chamber walls. Connection between the resulting submodels is accomplished via the adequate use of the heat balance method. The model is applied for two of the most commonly used engine insulation configurations under transient operation (load increase), with the variation of the thermal characteristics of the fluids surrounding the combustion chamber simulated in detail. An engine transient event was revealed to consist of two different characteristic thermal stages, which are distinguished and analysed. The importance of the rate of a specific variation towards the development of sharp temperature gradients (thermal shock) inside the sensitive ceramic materials is clearly revealed. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements at the initial and final stages of the transient variation, confirming the models validity.
    International Journal of Vehicle Design 01/1999; 22(3-4). DOI:10.1504/IJVD.1999.001865 · 0.24 Impact Factor
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    ABSTRACT: The present two zone model of a direct injection (DI) Diesel engine divides the cylinder contents into a non-burning zone of air and another homogeneous zone in which fuel is continuously supplied from the injector and burned with entrained air from the air zone. The growth of the fuel spray zone, which comprises a number of fuel-air conical jets equal to the injector nozzle holes, is carefully modelled by incorporating jet mixing, thus determining the amount of oxygen available for combustion. The mass, energy and state equations are applied in each of the two zones to yield local temperatures and cylinder pressure histories. The concentration of the various constituents in the exhaust gases are calculated by adopting a chemical equilibrium scheme for the C–H–O system of the 11 species considered, together with chemical rate equations for the calculation of nitric oxide (NO). A model for evaluation of the soot formation and oxidation rates is included. The theoretical results from the relevant computer program are compared very favourably with the measurements from an experimental investigation conducted on a fully automated test bed, standard “Hydra”, DI Diesel engine installed at the authors’ laboratory. In-cylinder pressure and temperature histories, nitric oxide concentration and soot density are among the interesting quantities tested for various loads and injection timings. As revealed, the model is sensitive to the selection of the constants of the fuel preparation and reaction sub-models, so that a relevant sensitivity analysis is undertaken. This leads to a better understanding of the physical mechanisms governed by these constants and also paves the way for construction of a reliable and relatively simple multi-zone model, which incorporates in each zone (packet) the philosophy of the present two zone model.
    Energy Conversion and Management 06/2004; DOI:10.1016/j.enconman.2003.09.012 · 3.59 Impact Factor

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