Gas transfer in internal combustion engines

The performance of an internal combustion engine, whether diesel or spark-ignition, two-stroke or four-stroke, naturally aspirated or supercharged, is directly determined by the mass of air introduced into the cylinder. This air mass determines the maximum quantity of fuel that can be introduced, and therefore the total energy available. During the engine cycle, this energy is transformed not only into mechanical energy on a shaft, but also into unburnt fuel, exhaust losses and thermal losses.

To optimize the quantity of air introduced into the cylinder, we need to study the unsteady flows that take place in the intake and exhaust systems of internal combustion engines. This optimization is carried out by determining the lengths and cross-sections of the ducts (supercharging by the Kadenacy effect), the volumes of the various elements (resonance of tubes on volumes: air filter or cylinder), as well as the characteristics of the valve train (diameter and number of valves, timing of lift laws, spread, maximum lift, maximum permissible acceleration, characteristics of the ports for two-stroke engines).

These considerations apply equally to reciprocating and rotary engines, which differ only in their kinematic designs for volume variation.

We begin by describing 1 the physical phenomena encountered when studying gas transfer in an engine, with a few examples of sensitivity to different parameters, such as distribution, heat exchange, pressure drop, acoustics and cross-sectional variations. We then present a numerical modeling approach for studying these phenomena. The equations that can be applied to study flows in pipes will be described 2 , as well as the main solution methods