A New Modeling to Predict the Fluid Dynamic Transient Phenomena in Ice Ducts 2008-01-2389

The prediction of the transient phenomena in reciprocating internal combustion engine (ICE) manifolds is of great importance in engine design (torque, power, etc…) as well as for the air fuel ratio (A/F) engine control. Those phenomena are dominated by the capacitive and inertial properties of a compressible flow, leading to the propagation of pressure waves traveling upstream and downstream the intake and exhaust manifolds. These can produce benefits or drawbacks in cylinder filling or emptying, so influencing the thermodynamical and environmental performances of the engine.

A new method for calculating the transient phenomena in engine manifolds is here presented in a form which is an improvement of a previous formulation presented by one of the author [1]. Following an electric analogy between voltage-speed of sound and current-fluid velocity, the method presents a wider formulation for the solution of the non-homoentropic 1-D advected wave equation in the Laplace domain. The method introduces a third fluid state variable (to take into account of the energy conservation together with the mass and momentum) represented by the entropy level. The mathematical representation of the boundary conditions to which usually is made reference in ICE has been also improved; according to this new formulation, they allow a very close representation of real engine manifolds geometries.

A validation of the model is presented according to experimental data measured on a series of ducts whose cross section varies in the direction of the fluid motion.