Catalytic Converters for Cold Start HC Emission Control
Figure 5.19 shows HC emissions on US EPA cycle beginning from the instant when the engine is started from cold. Also, the LEV and ULEV HC limits are shown on this figure.
Figure 5.19
HC emissions during cold start in US FTP cycle. LEV and ULEV emission limits are alsoshown.
From this figure it is observed that;
About 60 to 80% of total US FTP cycle HC emissions are produced during the first 2 minutes of vehicle operation after cold start.
To meet LEV standards catalyst should become functional within 80 seconds
For ULEV limts the catalyst should become functional within 50 seconds
• Electrically heated catalysts (EHC)
• Close-coupled catalysts
• Hydrocarbon traps
Electrically Heated Catalysts
The converters can be electrically heated before the engine started. In the metallic monoliths, metal honeycomb itself has been used as a heating element. Use of thin steel foils reduces thermal capacity of the catalyst. However, electrical heating still requires considerable energy to be drawn from the battery particularly in cold climates. Under cold ambient conditions the batteries are subjected to very high power drain. This becomes more difficult proposition as at the low ambient temperatures the battery activity is low and a high amount of energy is also required to crank and start the engine.
