IMPROVEMENTS OF BOUNDARY CONDITION MODELS FOR 1D ENGINE
THERMODYNAMIC AND GAS DYNAMIC SIMULATIONS
ENEA - Italian National Agency for New Technologies, Energy and the Environment
RTZ-Soft – Automotive Engineering and Software
Computer software which simulates the thermodynamic and gas dynamic of internal combustion engines, is used extensively during
design and development process.
This paper analyzes the 1D boundary calculations using the Method of Characteristics (MOC), in particular the flow from the cylinder
to the manifold and the multi-pipe junction model with pressure loss.
The Benson constant pressure outflow model has been modified setting the minimum (no flow) and maximum (sonic flow in the
duct) physical entropy levels during the iteration s. A sub iterative cycle has also been made when calculating the Riemann incident
and reflected variables in order to improve the convergence espec ially for lower valve area ratios (e.g. at the valve opening and
closing). An example to test the convergence has been reported and it has been obtained for all the valve area ratios (>10-6) with a
tolerance of 10-6 and with a number of iterations less tha n 45.
Sonic flows can be encountered in the exhaust manifolds of internal combustion engines (for example racing engines) and if more than
one manifold has flow to ward the junction a “Datum” manifold has to be defined in order to calculate the pressure losses for those
ducts with flow away from the junction. This paper reports some improvements of the multi-pipe pressure-loss junction model (SAE
2003-01-0370): a control for chocked flow has been added when solving the continuity equation and an " datum duct" has been built as
sum of all incoming flows, an averaged density, speed and area together with the pressure loss coefficients. Two tests have been
reported in order to show the results for the case when there is sonic flow for incoming flows and anoth...