Abstract
Keywords: unsteady gas flow, engine manifold design
Today, 1D engine performance and gas dynamics simulation codes are widely used tools in the design and development process of piston combustion engines. They are characterized by an outstanding combination of rapid runtime and high precision of results; thanks to the combination of 1D gas dynamic model in the manifold and 0D solving approach to all other elements (cylinders, turbochargers, plenums, etc.). Typical applications of these codes include prediction of performance parameters, manifold tuning, valve and ignition timing and cam profile optimization or turbocharger matching. They are also often used to provide boundary conditions for thermo-mechanical finite element or more complex CFD analyses. In order to obtain time-dependent state parameters of the unsteady gas flow throughout the manifold at defined engine speed and load conditions, the codes solve a set of three conservation laws (continuity, momentum and energy equations) of inviscid gas flow. Though they can take into account the phenomena of friction, heat transfer or even chemical reactions, they sometimes exhibit serious problems when dealing with varying-area geometries (nonstraight pipes). Features like bends, junctions, or plenums can be solved fairly well with one of the established methods (Gono, 2006), but tapered ducts, which are abundant features in engine manifold systems, are supposed to obey the so called quasi-1D formulation of equations.