Abstract
Unsteady flow in pipe elements can have significant effects on engineered products such as inlet and exhaust systems of internal combustion engines. These flows are considered onedimensional and the gas dynamics phenomena are described by a non-linear differential equation system which solves the continuity equation, the momentum equation, and the energy equation. The resolution of these equations requires a modeling of the boundary conditions where the flow perturbations are located, especially near the inlet and exhaust valves. It is then necessary to develop models which can predict the flow behavior with accuracy in order to determine the internal combustion engine filling and emptying.
The presented work is a part of a project whose aim is to improve the modelling of poppet valves. Due to technical problems, it is difficult to reproduce valve flow in hot conditions. Thus, a credible outflow configuration with hot gases is rarely tested. Consequently, valve models are tested and calibrated in normal temperature.
However, a literature survey shows that the discharge coefficient, Cd, is strongly temperaturedependant. Consequently, is the engine simulation calculated from a Cd computed in warm condition is as accurate as expected? Furthermore, even if the energy of the mass of air trapped in the cylinder is important, the enthalpy flows through the exhaust pipe is extremely important to study the warn of a catalytic converter.
In a first step, a pipe fitted with a cylinder head is tested at high temperature .The aim of this paper is to quantify the influence of the temperature in a representative geometry. Then, the results are analysed with a1-D valve model.
A comparison of the discharge coefficient measured at atmospheric and thermal condition was finally done. Results showed that the effect of temperature on this fundamental parameter is not negligible.
Keywords: Valve Model, Thermal effect, Measure – Computation comparison