Étude numérique et expérimentale d’un cycle thermodynamique dans un moteur diesel

Abstract

Internal combustion engines are an important part of the transport and power generation sector, consuming a large amount of fossil fuels. They alone consume about 70% of the world’s daily demand for crude oil, which is a concern for public authorities because of their polluting nature. Their optimisation and the design of new prototypes call on manufacturers to develop digital and experimental tools capable of reproducing the phenomena taking place within the engine cylinder throughout the thermodynamic cycle. Diesel engine modelling is generally represented by several models, including the 0D model. The 0D model is dominant because of its ability to reproduce state quantities in a relatively short time and the results are relatively close to the experimental ones. The main objective of this thesis is to write a computational code simulating the diesel cycle and solving speci c problems such as the valorisation of new energy sources, the reduction of high pressures and polluting emissions following the use of biofuels. The validation of the code is done using the numerical cylinder pressure of the cycle from the admission of gases into the combustion chamber to their exhaust compared to the experimental cylinder pressure obtained under the same conditions. The mathematical modelling is that of Krieger and Borman’s 0D model, which takes into account the nature of the fuel, allowing the combustion of the di erent fuels to be simulated under the constraint of heat losses at the walls. The characteristic peak of the temporal variation of the cylinder pressure in the numerical model is evaluated at 89 bars against 86 bars for the experimental one in the combustion of D100. In general, the validation results of the code showed an accuracy of 5 % compared to the experimental measurements of the two fuels tested at 100 % load. The results revealed that the use of biodiesel creates an increase in cylinder pressure of around 3.5% compared to conventional D100 diesel, thereby increasing engine e ciency. This led to a study of pressure reduction techniques. Under the constraint of heat loss models with a better accuracy of Woschni compared to other models with Eichelberg and Hohenberg, a decrease of the cylinder pressure of diesel and biodiesel with decreasing engine load of about 22.22% was shown when the engine load is reduced from 100 to 25 %. In dual-fuel mode, a reduction of 26.76% and 48.32% of nitrogen oxides is observed for diesel and biodiesel as primary fuel respectively.