Search Results

A common practice to improve vehicle fuel economy is to employ a fuel cut-off strategy on deceleration. This practice exposes the TWC exhaust catalyst to varying concentrations of oxygen depending on the vehicle control strategy. Since it is well known that exposure to oxygen at high temperature is deleterious to long term catalyst durability, it is important to understand the impact of oxygen concentration and temperature on catalyst performance. Simulated fuel cut agings at about 1%, 3%, and 9% oxygen concentration were compared to a full fuel cut aging (21% oxygen concentration). It was found that even small concentrations of oxygen at high temperature damaged catalyst performance. Deactivation increased with increasing oxygen concentration and increasing temperature.

The Federal Test Procedure (FTP) test contains an initial period, prior to the catalyst becoming fully activated, during which hydrocarbons escape the vehicle. These hydrocarbons constitute 60-80% of the total emitted over the entire FTP test. To meet future emission levels mandated by the California Air Resources Board, alternate technologies must be created that deal effectively with these cold start hydrocarbons. This paper describes an adsorbent bed/catalyst system that can trap approximately 70% of the available nonmethane hydrocarbons over the first two minutes of the FTP test. Importantly, the trap does not require bypass valves because of a unique heat exchange approach to catalytically consuming the trapped hydrocarbons, and because the trapping materials are unaffected by engine exhaust temperatures below 800°C. Experiments with a prototype system demonstrate that LEV emissions are possible.