Influence of transient phenomena in the discharge coefficient through the intake valve in an internal combustion engine

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The project of engine intake systems involves optimization of parameters such as the pipe length and diameter, junctions, and opening and closing times of the intake and exhaust valves. The correct sizing leads to an increase of the air mass admitted to the cylinders at the desired engine operational conditions. A suitable design of the intake valves in internal combustion engines is one of the factors that maximize the amount of intake air mass to the cylinder. The parameter that determines the maximization of the mass flow through the valves is called discharge coefficient. The mass flow through the valve is usually described by the compressible flow equation through a restriction, based on a dimensional analysis of an isentropic flow. In the present work, pressure variations caused by the valve movement were investigated experimentally considering an intake system. The objective was to study and compare the dynamic response of the flow through the intake valve. For this purpose, curves of mass flow rate and the dynamic pressure in several locations of the intake system were obtained. The experimental data were obtained from the intake system connected to a cylinder head. The cylinder head was installed in an air supply system consisted by a blower, a flow measurement device, and a reservoir chamber. The valves were driven by an electric motor with controlled rotational speed. The results showed that the correct design of the intake valve affects positively the air mass flow rate.cf201

Numerical analysis of the crosswind in small solar chimney

The solar chimney (or solar updraft tower) consists of a circular solar collector, a tower in the center of the collector, and turbines installed in the collector output or the tower entrance. The solar radiation passes through the translucent collector, reaches the ground surface and heats it. The air within the device is heated by the radiation emitted by the ground and by convection currents formed under the collector. The thermal energy is stored in the absorber layer of the ground when there is incidence of solar radiation and it is released from the ground when solar radiation is low. The density difference between the hot air inside the device and the ambient air creates convection currents that drive the air in the collector from the base to the top of the tower. Finally, the airflow in the tower drives the turbines which are coupled to electrical generators. The environmental winds influence the performance of the solar updraft towers in three main ways: heat losses by convection from the outer surface of the collector to the environment, heated air drag out of the cover and drag on the top of the chimney generating a suction effect and enhancing the upward flow in the tower. This work studied the influence of crosswinds on the system flow conditions through a numerical analysis using CFD. Results indicate that an increase on the environmental crosswinds speed from 0 to 25 m/s decreased the outlet temperature of the device in 0.3% and increased the outlet velocity in 50.26%, increasing the energetic efficiency of the device in 56.31%.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016