Diesel Particulate Filter (DPF) System Description
Diesel Particulate Filter (DPF) System Description
Exhaust Particulate Filter
The exhaust particulate filter (DPF) captures diesel exhaust gas particulates, preventing their release into the atmosphere. This is accomplished by forcing particulate-laden exhaust through a filter substrate of porous cells which removes the particulates from the exhaust gas. The exhaust gas enters the filter, but because every other cell of the filter is capped at the opposite end, the exhaust particulates cannot exit the cell. Instead, the exhaust gas passes through the porous walls of the cell leaving the particulates trapped on the cell wall. The cleaned exhaust gas exits the filter through the adjacent cell. The DPF is capable of reducing more than 90 percent of particulate matter (PM).
Exhaust Particulate Filter Operation
The exhaust particulate filter (DPF) filters particulate-laden diesel exhaust (1) through a porous cell which traps the particulate matter.
Diesel Particulate Filter Layout
1 - Exhaust Gas Temperature (EGT) Sensor 2
2 - Differential Pressure Sensor (DPS)
3 - Catalyst (DOC)
4 - Particulate Filter (DPF or EPF)
5 - DPS Pressure Lines
6 - Exhaust Gas Temperature (EGT) Sensor 1
Diesel Oxidation Catalyst
The diesel oxidation catalyst (DOC) (3) has two functions. One function is to reduce emissions of non methane hydro-carbons (NMHC) and carbon monoxide (CO), from the exhaust gases. The other function is to help start a regeneration event by converting the fuel-rich exhaust gases to heat. The engine control module (ECM) monitors the functionally of the DOC by determining if the exhaust gas temperature (EGT) sensor 1 (6) reaches a predetermined temperature during a regeneration event. The DOC and the exhaust particulate filter (DPF) (4) are downstream of the turbocharger, and are two separate components under the vehicle.
Exhaust Pressure Differential Sensor and Lines
The exhaust pressure differential sensor (2) measures the pressure difference between the inlet and outlet of the exhaust particulate filter (DPF) filter. When pressure difference has increased above a calibrated threshold, a high particulate loading condition is indicated. The engine control module (ECM) will command a regeneration event in order to restore the DPF. If the pressure differential continues to increase across the exhaust filter without a regeneration event the ECM will illuminate a DPF lamp or send a message to the drivers information center (DIC) referring the customer to the owners manual. The owner's manual will instruct the customer to drive the vehicle under the conditions necessary for a regeneration to take place. If these lamps and messages are ignored the ECM will eventually illuminate the MIL and revert to Reduced Engine Power which will require the vehicle to be serviced.
The exhaust pressure differential sensor wiring consists of the following circuits:
* A 5-volt reference supplied by the ECM
* A low reference supplied by the ECM
* A signal supplied by the differential pressure sensor to the ECM-The voltage is relative to the pressure differential changes in the particulate element. The ECM converts the signal voltage input to a pressure value.
The exhaust differential pressure sensor sample lines (5) are connected before and after the DPF. To provide the pressure sensor with accurate back pressure measurements, the DPS sample lines should have a continuous downward gradient, without sharp bends or kinks.
Normal Regeneration
Regeneration is the process of removing the captured particulates through incineration within the exhaust particulate filer. Elevated temperatures are created in the diesel oxidation catalyst (DOC) through a calibrated strategy in the engine control system.
Regeneration occurs when the engine control module (ECM) calculates that the particulate level in the filter has reached a calibrated threshold using a number of different factors, including engine run time, distance traveled, fuel used since the last regeneration, and the exhaust differential pressure. In general, the vehicle will need to be operate continuously at speeds above 48 km/h (30 mph) for approximately 20-30 minutes for a full and effective regeneration to complete. During regeneration the exhaust gases reach temperatures above 550°C (1,022°F). If a regeneration event is interrupted for any reason, it will continue where it left off, including the next key cycle, when the conditions are met for regeneration. Normal regeneration is transparent to the customer.
Service Regeneration
Caution: Tailpipe outlet exhaust temperature will be greater than 300°C (572°F) during service regeneration. To help prevent personal injury or property damage from fire or burns, perform the following:
1. Do not connect any shop exhaust removal hoses to the vehicle's tailpipe.
2. Park the vehicle outdoors and keep people, other vehicles, and combustible material away during service regeneration.
3. Do not leave the vehicle unattended.
Caution: To avoid extremely elevated exhaust temperatures, inspect and remove any debris or mud build up at the exhaust cooler located at the tailpipe.
Notice: Due to the elevated engine temperatures created while performing this procedure it is imperative to keep the front of vehicle in an open environment, away from any walls or buildings, this will ensure proper airflow across the radiator.
The Tech 2(R) is an essential tool that is required for service regeneration. Commanding a service regeneration is accomplished using the output control function. The vehicle will need to be parked outside the facility and away from nearby objects, such as other vehicles and buildings, due to the elevated exhaust gas temperature at the tail pipe during regeneration. The service regeneration can be terminated by pressing the brake pedal, commanding service regeneration OFF using the scan tool or disconnecting the Tech 2(R) from the vehicle.
Regeneration Process
A number of engine components are required to function together for the regeneration process to be performed. These components are the fuel injectors, turbocharger, intake air valve (IAV), fuel pressure control, and the intake air heater (IAH).
The regeneration process consists of several stages:
Warming up the oxidizing converter (DOC) to 350°C (662°F) by performing the following:
* Reducing air flow with the intake air valve
* Increasing or decreasing boost pressure with the turbocharger, depending on engine load
* Elevating the engine speed
* Reduce fuel rail pressure
* Retard fuel injection timing
* Add late fuel injection pulses. The added fuel is not combusted but is oxidized by the diesel oxidation catalyst (DOC) and exhaust particulate filter (DPF) to create heat.
Ash Loading
Ash is a non-combustible by product from normal oil consumption. Low Ash content engine oil (CJ-4 API) is required for vehicles with the exhaust particulate filter (DPF) system. Ash accumulation in the DPF will eventually cause a restriction in particulate filter. Regeneration will not burn off the ash, only particulate matter is burned off. To service an ash loaded DPF, the DPF will need to be removed from the vehicle and cleaned or replaced.
Exhaust Temperature Sensor Position 1
The exhaust gas temperature (EGT) sensor 1 (6) is a variable resistor that measures the temperature of the exhaust gases at the inlet of the DPF. The engine control module (ECM) supplies EGT sensor with a bias 5 volts on the signal circuit and a ground on the low reference circuit. When the EGT sensor is cold, the sensor resistance is high, as the temperature increases, the sensor resistance decreases. When sensor resistance is high, the ECM detects a high voltage on the signal circuit. When sensor resistance is low the ECM detects a lower voltage on the signal circuit. Proper exhaust gas temperatures at the inlet of the exhaust particulate filter (DPF) are crucial for proper operation and for initiating the regeneration process. A temperature that is too high in the DPF will cause the DPF substrate to melt or crack. Regeneration will be terminated at temperatures above 800°C (1,472°F). A temperature that is too low will not completely eliminate the particulates during regeneration. The ECM monitors the temperatures at the DPF inlet and outlet to regulate DPF temperatures.
Exhaust Temperature Sensor Position 2
The exhaust gas temperature (EGT) sensor 2 (1) is a variable resistor that measures the temperature of the exhaust gases at the outlet of the DPF. The engine control module (ECM) supplies the EGT sensor with a bias 5 volts on the signal circuit and a ground on the low reference circuit. When the EGT sensor is cold, the sensor resistance is high, as the temperature increases, the sensor resistance decreases. When sensor resistance is high, the ECM detects a high voltage on the signal circuit. When sensor resistance is low the ECM detects a lower voltage on the signal circuit. Temperatures at the outlet of the DPF are crucial to maintaining the integrity of the exhaust particulate filter (DPF) substrate. A temperature that is too high in the DPF outlet will cause the substrate to melt or crack. Regeneration will be terminated at temperatures above 800°C (1,472°F). A temperature that is too low will not completely eliminate the particulates during regeneration. The ECM monitors the temperatures at the DPF inlet and outlet to regulate DPF temperatures.