Modélisation et simulation des caractéristiques de combustion et de NO dans un moteur à allumage par compression : application au carburant biodiesel

Abstract

Global demand for energy has grown exponentially due to the increase of the world population, to the economic growth and to the technological evolution. This increase in overall energy demand can be explained in large part by the evolution of the transport sector. Unfortunately, the world’s oil reserves are depleting and in addition, the use of these fossil fuels is responsible of the environmental issues. So, research continues to offer other alternative energy resources to be part of a sustainable energy mix. The thesis follows this path and concerns the study of the biodiesel fuel which is from a renewable source of energy because of its immense potential. The biodiesel fuel used is based on waste cooking oil biodiesel (WCOBD). Our overall goal is to improve the energy performance of compression ignition engines operating with biodiesel fuels and to reduce NO emissions. Within the framework of this thesis, a thermodynamic approach was used for the modeling of the various physical phenomena that occur in the chamber of combustion of a compression ignition engine running with biodiesel fuel and with conventional diesel fuel. This phenomeno-logical model describes the whole physical phenomena, which occur during combustion, such as vaporization, injection, turbulence and the impact of chemistry on heat release and they are modeled using sub-models describing each of these physical phenomena. This two zone thermo-dynamic phenomenological model of combustion which predicts the pressure, the temperature, the different energy performances and the NO emissions. The technique of steam injection added reduces NO emissions and improves performances. Biodiesel fuels and conventional fuels are composed of many different classes of oxygenated hydrocarbons and hydrocarbons, it would be very hard to conduct meaningful experiments or simulations with such a large number of chemicals contained in these fuels. In order to overcome this problem, surrogates and chemical equilibrium modeling are used to meet these requirements. The comparison of the calculated and experimental values of nitric oxide concentrations in the exhaust for the two fuels shows a very satisfactory coincidence. The calculated and measured nitric oxide concentration values of biodiesel fuel are 927.7 ppm and 954.4 ppm, respectively. While the values of calculated and experimental concentration of nitric oxides in diesel fuel are 1004.4 ppm and 1019.4 ppm, respectively. As perspectives, the computational fluid dynamics of the combustion of biodiesel fuel in compression ignition engines and chemical equilibrium modeling combustion products to find surrogates molecules for biodiesel fuels are being considered.