Diesel Particulate Filters

A Diesel Particulate Filter collects particulate matter in the exhaust stream by means of physical filtration.  
Diesel Particulate Filters
  • The Diameter of the soot particles are close to 0.09 microns, which are made mainly by carbon and hydrocarbons
  • The principle of the diesel particulate filter (DPF) is to collect the sooty particles and periodically burn them off
  • The natural combustion of those particles takes place around 550°C, whereas the initial temperature reached by exhaust gases in the exhaust manifold is around 150°C
Particulate Matter (PM)
In a perfect combustion, carbon dioxide, water and nitrogen are the end products. The incomplete combustion of diesel fuel results in emissions that include oxides of nitrogen (NOx), carbon monoxide (CO), Carbon dioxide (CO2), water (H2O) and unburned hydrocarbons (HC). There are also un-burnt carbon particles, as well as engine oils, debris, soot and ash particulates which are known as particulate matter (PM). This diesel particulate matter (DPM) is the visible cloud of black smoke that appears from the engine start-up and continues to appear when the engine is running. DPMS can be categorized into two groups. Particles of 2.5 microns to 10 microns, and particles of less than 2.5 microns in size. More than 99% are in the sub 2.5 microns range. They are all damaging to your health.
DPF: Passive Regeneration

Passive regeneration involves the slow environment-protecting conversion of the particulates deposited in the filter into carbon dioxide. This regeneration process comes into effect when the filters temperature reaches 250°C+ and occurs continuously when the vehicle is being driven at higher engine loads and speeds. No special engine management intervention is initiated during passive regeneration, allowing the engine to operate as normal.

Only a portion of the particulates are converted to carbon dioxide during passive regeneration and due to chemical reaction this process is only effective with the temperature range of 250°+to 500°C+. Above this temperature range the conversion efficiency of the particulates into carbon dioxide subsides as the temperature of the filter increases.

Unfortunately not all vehicles get the required long journey necessary to complete a passive regeneration of the DPF System so manufacturers have has to adapt the technology and design-in an "active" regeneration process controlled by the Engine Control Unit (ECU).

Advanced Particulate Filter Technologies for Direct Injection Gasoline Engine Applications: Part 2

Future emissions regulations without compromising vehicle performance or durability.

Diesel Particulate Filters for original equipment applications remove particulate matter from engine exhaust gases in a closed system. When gases carrying particulate matter flow through the filter's substrate walls, particulate matter is trapped and collected in the filter. A regeneration process, triggered by the engine management system, then burns off the soot using either a fuel borne additive or a catalytic filter coating.

Gasoline particulate filters use the same type of wall-flow substrates as diesel particulate filters and can be included in the exhaust system in addition to the series three-way catalyst or the catalyst coating can be directly applied to the filter substrate to form a four-way catalyst. Improvements in the acoustic function of the gasoline particulate filter make it possible to reduce exhaust volume,  helping to reduce backpressure, increase performance, reduce weight and save cost.

Advanced Particulate Filter Technologies for Direct Injection Gasoline Engine Applications: Part 1

The developing of gasoline particulate filters for 2017 model year light vehicles. These filters are designed for gasoline direct injection (GDI) engines to reduce particulate emissions in compliance with the Euro 6C emissions regulation, which takes effect on September 1st 2017. 

Systems integration and advanced manufacturing capabilities, we provide customers flexible solutions for any powertrain to meet regulations without compromising vehicle performance or durability. GDI engines help improve fuel economy and therefore refuse CO2 emissions however, they can have higher particulate emissions due to shorter fuel/air mixing times in the cylinder compared to multiport fuel injection engines.

Advanced fuel injection strategies are currently used to control gasoline particulate emissions in cylinder but they are designed for a particular emission test cycle and may be less effective under real driving conditions. Gasoline particulate filters effectively control particulate emissions under all opening conditions.

Active DPF Regeneration: DPF Coordinator Module

The DPF coordinator responds to a regeneration request from the supervisor module by initiating and coordinating the following DPF regeneration specific requests: EGR cut off, Boost pressure control, Engine load increase, Control of gas pressure and temperature in the intake manifold, and Fuel injection control.

Once regeneration request is set by the supervisor module the coordinator requests EGR cut off, and regeneration specific boost pressure control. It awaits feedback signal from the EGR system indicating that the valve is shut. Once this occurs, the coordinator initiates requests to increase engine load by activating electric consumers and controlling the intake air temperature and pressure.

Once it receives a confirmation that intake conditions are adequately controlled or expiration of calibratable time, it switches to a state waiting for an accelerator pedal release manoeuvre from the driver. If this occurs or a calibratable time elapses, the coordinator initiates a request to control fuel injections to increase exhaust gas temperature.

Diesel Particulate Filters: Active DPF using additives

When the soot loading in the filter reaches a set limit (about 45%) the ECU will release an additive (EOLYS) into the fuel system. The additive reduces the burning temperature of the particulates by 100°C, therefore reducing it from 550°C to 450°C. Once the filter is empty the ECU will switch off the additive. There are two additive systems, one injects the EOLYS directly into the fuel line, the other releases the EOLYS into the fuel tank, this method relies on a pressure sensor on the fuel filler cap.

Active DPF Regeneration: During the active regeneration period

The turbocharges are maintained in the fully open position to minimize heat transmission from the exhaust gas to the turbocharges and to reduce the rate of gas flow through the particulate filter. This enables optimum heating of the particulate filter. if the driver demands a higher torque the turbochargers will respond by closing the vanes as required.

The throttle is closed as this assists in increasing the exhaust gas temperature and reducing the rate of exhaust gas flow, both of which increase the speed at which particulate filter is heated.

The exhaust gas recirculation (EGR) valve is closed as the use of EGR lowers exhaust gas temperatures and therefore makes it difficult to achieve the regeneration temperature in the particulate filter.

The glow plugs are sometimes activated to provide additional heat in raising the temperature of the particulate filter. To maintain flow plug serviceability the activation period of the glow plugs is restricted to 40 seconds

Active DPF Regeneration: Part 2

If the DPF warning light comes on you will need to start the regeneration process. This can be done by driving at 2500 RPM for more than 20 minutes, or according to the manufacturers recommendations (as explained in the manufacturers service handbook).

If you continue to drive the car and ignore the warning light the filter will continue to fill with soot and around 70%+full the engine management light and the glow plug light will start flashing and sometimes the vehicle will go into limp mode causing a lack of power. When the DPF reaches 90% full it will need replacing.

Active DPF Regeneration: Part 1

First  post-injection retards combustion inside the cylinder to increase the heat of the exhaust gas. Second post-injection injects fuel late in the power stroke cycle; fuel partly combusts in the cylinder but also sweeps down the exhaust where unburned fuel triggers an exothermal event in the catalyst, raising the filters temperature further.

Active regeneration takes approximately 20 minutes to complete. The first phase is to raise the temperature of the filter to particulate combustion temperature of 500°C+. In the second phase the temperature is raised to 600°C+, the optimum particulate combustion temperature.

This temperature is maintained for 15 to 20 minutes to ensure complete incineration of the particulates captured in the filter. The incinerated particulates produce carbon dioxide and water. Active regeneration is controlled to achieve a target temperature of 600°C+ at the inlet of the particulate filter without exceeding the temperature limits of the turbocharges and close-coupled catalysts.

Active DPF
The CRT can form part of the actively regenerated DPF System in which the HC content of the exhaust stream is periodically enriched by in-cylinder post injection (up to 8 times more fuel injected). The HC's are burnt over the catalyst, raising the temperature within the DPF to over 550° resulting in the combustion of the collected PM.
Silicone Carbide Wall Flow Filters
The second most popular filter material is silicone carbide, or SIC. It has a higher melting point than cordierite (2700°C+) however it is not as stable thermally, making packaging an issue. Small SIC cores are made of single pieces, while larger cores are made in segments, which are separated by a special cement so that heat expansion of the core will be taken up by the cement. SIC cores are usually more expensive than cordierite cores, however they are manufactured in similar sizes, and one can often be used to replace the other.
DPF Removal

We strongly advise people to not do it as it is illegal and your vehicle WILL fail its MOT. Numerous customers that have had engine problems due to DPF Removals and ECU re-mapping, they have ended up paying out thousands of pounds trying to rectify the related faults.

Newer vehicles have their full build specification logged on a master computer, so if the DPF is removed and the ECU is re-mapped when the car is connected to the dealerships master computer a PR Code will identify that the engine has been enhanced, so voiding the manufactures warranty. You will be breaking the law and liable to prosecution to use a vehicle modified in this way in any ULEZ/LEZ (low emission zones).

Cordierite Wall Flow Filters

The Most Common Filter is made of Cordierite.

Cordierite filters provide excellent filtration efficiency, are (relatively) inexpensive and have thermal properties that make packaging them for installation in the vehicle simple.

How does a Diesel Particulate Filter work?
A Diesel Particulate Filter collects particulate matter in the exhaust stream by means of physical filtration. Soot particles from diesel exhausts are trapped by a porous ceramic substrate inside the filter and collected on the walls. When the maximum 'fill level' is reached one of several methods is employed to clear the filter of the collected particulates. It is only necessary to replace the DPF when this process breaks down and the filter becomes irreversibly clogged.