Exhaust Catalyst and Exhaust System

EXHAUST CATALYST AND EXHAUST SYSTEM

The exhaust catalyst and exhaust system consists of the following components. For additional component information, refer to Engine Control Components. Engine Control Components
- Three exhaust gas temperature (EGT) sensors that measure the exhaust gas temperature.
- An oxidation catalytic converter (OC) that reduces emissions and assists in diesel particulate filter regeneration.
- A diesel particulate filter pressure sensor that measures the gauge pressure of the exhaust gas before the diesel particulate filter.
- A diesel particulate filter that traps soot and ash particulates.

Exhaust System:

Overview
The purpose of the exhaust catalyst and exhaust system is to convey the exhaust gas from the engine to the atmosphere and reduce the tailpipe emissions of hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and diesel particulates. The diesel particulates, soot and ash, are captured and periodically reduced by the diesel particulate filter regeneration cycle.


The exhaust gas and particulates are directed away from the engine through the exhaust manifold. The exhaust gas concentrations are then reduced to acceptable levels as the exhaust gas passes through the OC. Since the particulates are components of the exhaust gas, some soot particulates may deposit on the OC. These particulates are removed during regeneration. The reduced emissions exhaust gas and particulates continue to the diesel particulate filter. In the diesel particulate filter, the exhaust gas and particulates flow through the channels of substrate filter. The channels of the substrate filter are alternately blocked, so the exhaust gas and particulates are forced to pass through the filter medium and into the adjoining channels to exit the filter. As the exhaust gas passes through the filter medium, any particulates larger than the pores of the filter are removed from the flow of exhaust gas and trapped for diesel particulate filter regeneration. The reduced emissions exhaust gas and any remaining particulates flow through the muffler and tailpipe into the atmosphere.

Diesel Particulate Filter Regeneration
The diesel particulate filter regeneration occurs during normal vehicle operation. The powertrain control module (PCM) may regenerate the diesel particulate filter at idle. During the diesel particulate filter regeneration, fuel is injected into the cylinder after the main combustion. The extra fuel increases the temperature of the exhaust gas and lights-off the OC. The temperature of the exhaust gas increases to greater than 550°C (1,022°F) at the OC and diesel particulate filter. At this temperature soot burns and is reduced to ash. Soot particulates that may have accumulated on the OC or in the diesel particulate filter are burned and the ash is trapped in the diesel particulate filter. The ash particulates that remain in the diesel particulate filter are mainly comprised of metallic compounds generated during combustion and from corrosion in the exhaust system.