Abstract
Abstract: Nowadays, research in the internal combustion engine field is focusing on detailed understanding of the processes that take place in certain parts of the aggregate, and can have a great influence on the engine´s performance and pollution levels. Thus, in several experiments the clogging of the air filter is studied and its´ influence on engine running characteristics. Such research is developed in this paper, in which using the i-x air-fuel diagram, one can simulate a series of values for pressure, temperature and intake air humidity before and after the filter for a spark ignition engine. The aim is to evaluate the final temperature of the air-fuel mixture near the inlet valve. Temperature and mixture composition were determined using a numerical method based on the equations used in building the i-x air-gasoline diagram. Also, the mixing of air with fuel was considered adiabatic, as the process takes place in a short period of time. By determining the temperature near the inlet valve, the mixture´s composition can be evaluated. Thus, the fraction of fuel that enters the engine as vapor and the part that remains in liquid state can be determined. These evaluations were done for different manifold absolute pressure and intake air humidity values. A nonliniar variation of the mixture´s final temperature with the air intake temperature was observed in all the studied cases. The curves´ trend changes when crossing from the saturated domain (mixture with vapor and liquid fuel) into the nonsaturated one (fuel as vapor only). Also, the deviation from a liniar variation is influenced by the intake air´s relative humidity, as is the final mixture´s composition.
Keywords: Intake, Temperature, Mixture, Enthalpy, Air humidity, Pressure