Correlation Between Instantaneous Pattern of Intake Air Motion and Combustion Behaviour in a S.I.Turbocharged Engine

Improvement of combustion efficiency is an effective way to increase engine torque and to reduce fuel consumption simultaneously. For gasoline engines, however, especially at medium and high load, combustion efficiency is limited by knock. It is well known that intake air motion into the cylinder influences combustion speed and knock resistance.

During the development activity of a S.I. (Spark Ignition) turbocharged engine it was noticed that not only the maximum intensity of air motion, but also its instantaneous pattern had an impact on combustion behaviour. A methodology which estimates the instantaneous pattern of intake air flow through the valves, based on in-cylinder pressure measurements and on flow test rig data, was found. A further verification of this methodology through a computational 1-D thermodynamic cycle model was performed. The methodology predictive capability was tested in terms of evaluating the effect on the combustion, i.e. on the engine torque, due to an engine intake system modification, with advantages in time spent during engine development activity.