CAP 6D4909 - Caterpillar

To meet current emissions legislation requirements, a small amount of certain chemical compounds that are emitted by the engine must not be allowed to enter the atmosphere.
Illustration 1 g03320982
Typical example
(1) Aftertreatment Regeneration Device (ARD)
(2) Diesel Oxidation Catalyst (DOC)
(3) Diesel Particulate Filter (DPF) The CEM for the engine consists of the following components.
Aftertreatment Regeneration Device (ARD)
Diesel Oxidation Catalyst (DOC)
Diesel Particulate Filter (DPF)The Diesel Oxidation Catalyst (DOC) oxidizes the carbon monoxide and the hydrocarbons that are not burnt in the exhaust gas into carbon dioxide and water. This is a through flow device that will continue to operate during all normal engine operating conditions.The wall flow Diesel Particulate Filter (DPF) collects all solid particulate matter in the exhaust gas.The Aftertreatment Regeneration Device (ARD) increases the exhaust gas temperature to a sufficient level. The soot that is collected in the DPF is oxidized.If applicable, a flexible exhaust pipe can connect the engine to the Clean Emissions Module (CEM). Refer to Disassembly and Assembly for the correct procedure to install the flexible exhaust pipe.The solid particulate matter that is collected by the DPF consists of soot (carbon) from incomplete combustion of the fuel and inorganic ash from the combustion of any oil in the cylinder.The rate of accumulation of ash is slow. The filter is designed to contain all the ash that is produced until the defined service interval. Refer to Operation and Maintenance Manual for more information.The soot that is collected must be removed at regular intervals by a process of regeneration.The wall flow DPF continuously regenerates at modest temperatures, using passive regeneration to continually control soot loading.Active regeneration occurs when the engine does not create enough heat in order to regenerate the DPF.Air is supplied to the ARD through pressurized air from the turbocharger and air pump. Fuel is supplied from the leakoff line to the ARD.Fuel is injected onto a wire gauze by the first injector. The fuel is ignited by the glow plug. The ARD is air cooled.The combustion of the fuel generates heat. Once the temperature recorded by the inlet temperature sensor has reached 300° C (572° F), the second injector will inject fuel into the exhaust gas stream. The fuel from the second injector ignites when the fuel comes into contact with the face of the DOC due to the heat created by first injection event.The DOC oxidizes the soot into carbon dioxide, which then passes through the filter and into the atmosphere.The ARD may automatically switch ON and OFF. The ARD may be manually controlled by the operator. The ARD is controlled by the sensor for the soot level. The sensor for the level of soot will ensure that the level of soot in the filter is kept within limits. This is referred to as a regeneration of the filter.In order to regenerate the DPF at the right time, the engine ECM must know how much soot is in the DPF. Measurement of soot is accomplished through the following means:
Delta pressure measurement across the DPF
Calculated model