Close-coupled catalyst

INTERNAL COMBUSTION ENGINE + CLOSE COUPLED CATALYST + TWC WITH FEEDBACK CONTROL... 

Figure 12 THC, CO, and NO emissions in the ECE/EUDC test from the vehicle used in Fig. 9 fitted with a close-coupled catalyst.

Fig. 4. Cumulative hydrocarbon emissions measured during the federal test procedure (FTP cycle) on a US 1995 car (1) engine-out emissions (2) tailpipe emissions with close-coupled catalyst. (Heck and Farrauto 1997.)...

The effects of high temperature calcination has been studied by different authors due to their inherent importance under the fuel-cut conditions, where the TWCs are subjected to extremely high temperatures under oxidising conditions (above 1273 K in the close-coupled catalyst). 

As shown in sect. 3, Ce02-Zr02 mixed oxides represent a fundamental advance of TWC technology from the advent of the Ce02 in exhaust control in the early 1980s. As discussed above, particularly thermal stability of both surface area and OSC are positively affected by the insertion of Zr02 in the catalyst formulation. Consequently, the development of the close-coupled catalyst has become a reality. This technology... 

Vehicle Performance In an attempt to meet the strict LEV/ULEV standards, a preliminary close coupled and underfloor catalyst system was evaluated. The close coupled catalyst was a 0.4 liter unit containing 10.6 g/1 of Pd. The underfloor converter contains 2 units with a combined volume of 2.67 liters and a Pd loading of 3.53 g/1. The system was aged on a multi-step dynamometer cycle for 55 hours in which the close couple converter sees a maximum bed temperature of 950°C and the underfloor catalyst 800°C. The FTP test evaluations are conducted on a 1993 vehicle with a 2.21 DOHC engine. 

Recent developments in Pd catalyst teclinology have been demonstrated to improve the durability of the low temperature lightoff properties of this catalyst after repeated exposure to relatively high temperature exhaust [30,32,35]. Thus, these new catalyst formulations show promise for application as a close-coupled catalyst which can reach HC lightoff rapidly after cold-start. These new formulations may also be more resistant to sulfur poisoning. 

All of these approaches contain vmderfloor catalysts of various compositions. It has become clear with the development of high-temperature, close-coupled catalyst that this is the leading technology for LEV, ULEV, and SULEV applications. It is used in combination with underfloor catalysts. A brief description of each of the various candidate technologies follows, along with details of the close-coupled catalyst development. 

Fig. 14. Close-coupled catalyst with an underfloor catalyst can meet ULEV emissions for many four- and six-cylinder vehicles.

Low heat capacity exhaust pipe Pd close-coupled catalyst on 1200 cpsi Underfloor catalysts, TWC and HC trap hybrid catalyst Two secondary HEGO sensor... 

Close-coupled catalyst Underfloor catalyst 1.1- L ceramic 3 mil 600 cpsi 1.1- L ceramic 4 mil 400 cpsi 1.1-L ceramic 3 mil 900 cpsi 1.3-L 3 mil 600 cpsi (HC adsorbing TWC)... 

These reductions in emissions were measured after the close-coupled catalyst of the different cell geometries (90). 

In fact, depending on the driving, it is not unusual for a traditional TWC to meet temperatures up to 900 °C during operation. Furthermore, because of the continuously stricter limits for automotive pollutants demanded, the control of cold-start emissions through the concept of close-coupled catalysts (CCCs) has to... 

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