Abstract
It is well known that spark ignition internal combustion engines for aeronautical applications operate within a specific temperature range to avoid structural damages, detonations and loss of efficiency of the combustion process. An accurate assessment of the cooling system performance is a crucial aspect in order to guarantee broad operating conditions of the engine. In this framework, the use of a Conjugate Heat Transfer method is a proper choice, since it allows to estimate both the heat fluxes between the engine walls and the cooling air and the temperature distribution along the outer wall surfaces of the engine, and to perform parametric analyses by varying the engine operating conditions. In this work, the air-cooling system of a 4-cylinder spark ignition engine, designed by CMD Engine Company for aeronautical applications, is analysed in order to evaluate the amount of the air mass flow rate to guarantee the heat transfer under full load operating conditions. A preliminary validation of the model is performed by comparing the results with available experimental data. A parametric study is also performed to assess the influence of the controlling parameters on the cooling system efficiency. This study is carried out by varying the inlet air mass flow rate from 1.0 kg/s to 1.5 kg/s and the temperature of the inner wall surfaces of the engine combustion chambers from 390 K to 430 K.
Highlights
An increase of the load conditions of Internal Combustion Engines (ICEs) causes an increase of the engine wall temperatures
It is well known that spark ignition internal combustion engines for aeronautical applications operate within a specific temperature range to avoid structural damages, detonations and loss of efficiency of the combustion process
An accurate assessment of the cooling system performance is a crucial aspect in order to guarantee the operating conditions of the engine
Summary
An increase of the load conditions of Internal Combustion Engines (ICEs) causes an increase of the engine wall temperatures. High temperature of the engine walls leads to several problems as, for instance, the deterioration of the cylinder lubricating oil and the seizure of the engine components [1]. The temperature of the combustion chamber liner on the gas-side surface should be generally kept below about 180°C, in order to preserve the thermal stability of the lubricating oil and to reduce the thermal stresses [2]. It has been proven that the heattransfer rate to coolant under full load conditions of a spark ignition engine is about 60-70 % of the engine brake power [3]. The amount of transferred heat can be evaluated by employing semi-empirical relations, such as Annand's correlation, which provide the wall heat fluxes in the combustion chamber during the working cycle [4]
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