Scavenging in a turbocharged gasoline engine

The phenomenon of air escaping the engine intake directly to the exhaust during valve overlap is commonly known as scavenging. This phenomenon is primarily observed at low-speed, high-load in engines with significant overlap between intake valve opening and exhaust valve closing. Evaluation on a turbocharged-gasoline engine shows increased low-speed torque when operating under scavenging conditions. This paper investigates the occurrence of scavenging and analyzes its consequences. A methodology is presented to infer the amount of scavenging using airflow and in-cylinder pressure measurements. Scavenging increases catalyst exotherm when operating with stoichiometric exhaust. A model is proposed to predict the additional exotherm.

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