Air Intake System Evaporation Emissions: Physical Description and Solutions 2008-01-0627
Reducing evaporation emission is one of the most important targets during vehicle development nowadays. Apart from the emissions while the vehicle is in operation, evaporation emissions occur after the engine is turned off. Up to 30 % of these emissions can originate from the Air Intake System (AIS).
Today, Hydro Carbon Adsorbers (HCA) are already used as a part of the AIS to reduce evaporation emissions , . Usually the HCA contains activated carbon or zeolite. HC emissions are adsorbed by the HCA during and after the engine shut down. When the engine is running, the HCA is purged with the intake air. The HC storage principle is well known for carbon canisters .
HCAs were initially designed for existing AIS. So far, the pressure drop of the system was considered to be the most important design parameter while designing the AIS. Due to government regulations, more advanced requirements are established and hence sophistication in design is needed to meet new targets. This can only be achieved by having a complete understanding of the design boundary, otherwise known as package space.
This paper explains the HC transportation process in detail after the engine is shut down, by means of measured pressure, temperature and concentration gradients. Together with the emission sources such as intake ports (fuel films), injectors, crankcase (blow by), etc. and geometrical specifications like volume of the crankcase or the AIS, necessary information can be obtained for an optimal HCA design. Based on this, the available solutions are analyzed and compared.