1. Passive Generation :
Inside the aftertreatment device (ATD), the exhaust first passes over the diesel oxidation catalyst (DOC), then passes through the diesel particulate filter, which traps soot particles. Passive regeneration happens when heat in the engine builds to the point where soot, or carbon, is combined with oxygen to create carbon dioxide. Since carbon dioxide is a gas, it can pass through the filter. Ash, on the other hand, is already a byproduct of combustion, so no amount of heat from the engine can convert it. Over time, the ash will build up to the point where the filter has to be physically removed and cleaned. This filter can then be reinstalled and reused. Passive regeneration occurs as the vehicle is driven normally under load; the driver is not aware that it is happening. It may not always keep the DPF clean over the course of the workday, so the filter may have to undergo active regeneration.
2. Active Generation :
passive regeneration is part of normal engine operation, however active regeneration requires the engine to take action. For example, a truck fully loaded with 80,000 pounds moving down the highway will create enough heat in the engine for a chemical reaction to occur—which is passive regeneration. Active regeneration takes place when the engine isn’t creating the heat it needs. For example, this may occur in a truck that’s not fully loaded. Once the soot level reaches a certain point, the engine injects fuel into the exhaust stream, which goes over the oxidation catalyst and oxidizes the fuel to create heat. The heat created from the fuel oxidizing is then used to convert soot to carbon dioxide.
Both active and passive regeneration happen automatically and without driver input. Active regeneration can occur automatically any time the vehicle is moving. The exhaust gas temperature could reach 1500℉ (800℃).
Active regeneration is unknown to the driver with the exception of some additional dashboard lamps. The biggest sign to look for to determine if it is taking place is the high exhaust temp light, which will turn on once the aftertreatment doser starts to inject, increasing the temperature in the aftertreatment device.
When operating conditions do not allow for DPF cleaning by active or passive regeneration, the vehicle may require an operator activated parked regeneration.
In order for this to take place, the vehicle must be standing still. The driver or technician brings the engine to operating temperature and initiates the parked regeneration by activating the dash controls. This may take anywhere from 20 minutes to an hour, depending on ambient conditions and type of engine or DPF system.
