Diesel Particulate Filters(DPF)

Diesel particulate filters (DPF) are devices that physically arrest diesel particulates to inhibit their discharge to the atmosphere. Diesel particulate filter materials have been developed that show remarkable filtration efficiencies, in excess of 90%, as well as good mechanical and thermal toughness. Diesel particulate filters have become the most effective technology for the stoppage of diesel particulate emissions which includes particle mass and numbers—with high efficiencies. Due to the particle deposition mechanisms in these devices, filters are most effective in regulating the solid fraction of diesel particulates, including elemental carbon (soot) and black smoke emission.

Operation of DPF

Diesel particulate filters function by trapping soot particles from the engine exhaust, avoiding them from getting into the environment.  Contrasting to a catalytic converter which is considered to reduce gas-phase emissions flowing through the catalyst, the particulate filter is intended to trap and keep the solid particles till the particles can be oxidized in the DPF, via a process called regeneration.

In order to decrease filter pressure drop due to soot accumulation, the filter is regenerated through a processes oxidizes the soot.  There are two major categories of regeneration process, although most commercial applications practice some mixture of the two.  This is accurate with vehicles or equipments experiencing lengthy periods of low exhaust temperature operation, such as long periods of idle or low speed/load operations.

Active Regeneration

Active regeneration needs the addition of heat to the exhaust to upsurge the temperature of the soot to the point at which it will oxidize in the presence of surplus oxygen in the exhaust.  The combustion of soot in oxygen usually requires temperatures above 550 °C.  Since these high temperatures usually do not occur during standard engine operation, a number of tactics are used to increase the exhaust temperature.  Active regeneration systems may contain the use of a diesel burner to directly heat the exhaust arriving the DPF over the catalyst as a means for aggregating the DPF temperature.

Passive Regeneration

Passive regeneration does not involve additional energy to carry out the regeneration process. Instead, this approach depend on the oxidation of soot in the presence of NO2, which can happen at much lower temperatures in the array of 250 °C to 400 °C. A catalyst is used to convert NO present in the exhaust to NO2.  These catalysts involve the use of costly metals to enable the reaction. Platinum (Pt), in particular, which increases the additional cost to the system.

When your vehicle shows second stage DPF warning lights it will go in to ‘limp mode’ and should be taken to your garage or dealer to determine the level of the problem.

Forced Regeneration 

This involves the garage using a computer program to run the car, starting a regeneration of the DPF.  This will also involve altering the engine oil & oil filter.

In an ideal case, if engine operation outcomes in a certain extent of time spent within this passive regeneration “temperature window” then active regeneration is not required.  In fact, low temperature operation may take place for extended periods of time, such as long periods of sluggish or low load operation, mostly in cold climates, and some active regeneration is still needed.  In the deficiency of active regeneration, periods of low temperature operation may be accompanied by periods of high temperature operation to encourage passive regeneration.

In order to decrease fuel consumption, passive regeneration is favored, although most commercial systems still use active regeneration to variable degrees, depending on the drive cycle and operating situations. Irrespective of the regeneration method, the oxidation of soot (whether active or passive) gives us incombustible material, or ash, which cannot be burned, and residues in the DPF.  Knowing the key differences between ash and soot, as well as their impressions on DPF performance is vital when picking up the most suitable cleaning technique for the filter.

Emission Performance

All SXS diesel particulate filters deliver high declines of diesel particulate matter emissions. The catalyst coated filters will moreover decrease harmful gases such as CO, HC and HCHO. A DPF gathers diesel particulates in a diesel engine’s exhaust through a filtering process, and regular, proper maintenance is essential to make sure it continues to avoid the particulates from entering the atmosphere. In case when soot and ash builds up in a DPF, it limits system flow and creates substantial back pressure. A number of undesirable problems can cause from neglecting DPF maintenance, including:

  • Plugged DPF.
  • Low vehicle power.
  • Cracked DPF.
  • Melted filters.
  • Engine damage.

If you make DPF ash cleaning a typical procedure in all of your annual preventive maintenance schedules, you will reduce 99 percent of your DPF glitches. The quality of the DPF cleaning process will also govern how long it will be before a vehicle starts to display symptoms of ash and soot buildup.

How to clear a blocked DPF

Use good quality fuel. High Cetane fuel from key brands is loaded with additives which help burn off the particles. Cheap fuel usually increases the problem. Shell fuels are often recommended. Tests have revealed that this burns cleaner and leaves fewer deposits in your engine.

Avoid short journeys where the engine does not warm up completely and trips where the car is not able to continue 2000rpm for 5 mins.

Use a decent quality fuel additive such as BG244 to maintain a fresh and efficient engine.

Here is a general guide. Warm up the engine to operating temperature, then drive it for 15 minutes at constant speed on a street. Aim to keep the revolutions above 2000rpm for this period. The heat produced will aid to clean the DPF filter and the cars regeneration cycle will typically kick in under these circumstances. Add some BG244 to your tank and go for a long highway run at 70mph again keeping the revolutions above 2000 rpm. Other cleaners are accessible but BG244 is the most effective on the market. Always fill the tank with diesel as it helps a lot. Once you clear the DPF you shouldn’t get any problem until the next refill. Do not overlook the warning light of DPF blockage, take the car on a long road as soon as possible and follow the procedures mentioned otherwise engine management light would come on and car would go in limp mode and would not attain a speed.

What causes DPF Blockage

Every vehicle type & engine combination can have different reasons as to why the filter blocks. The degree of particulates generated by the engine, the quality of the fuel, quality of the oil, driving flair, even the location of the DPF in the exhaust system can all add to the filter blocking or not regenerating completely.

Generally, the problems arise in around urban stop start driving where the regeneration procedure might not complete. A warning light will illuminate or a message specifying the DPF is full displays on the dash. If you carry on to drive in the same manner, the soot build up will rise until other warning lights illuminate and the vehicle will go into ‘limp’ mode, where driving speed is limited.

This warning stage will now include a visit to the mechanic to carry out a forced regeneration on the filter, where filters that cannot be regenerated will then cost you to change the filter. Some of the reasons for the same are,

  • Use low ash engine oil: Not using the correct oil stated for your engine can considerably add to the soot buildup in the DPF.
  • 100% Diesel Bio Fuel: Using these Bio Fuels can also add to extra soot build up loading in your DPF as the Bio Fuel may not burn as ‘clean’.
  • Temperature: The DPF trusts on temperature to carry out a filter regeneration, at around 600°C, so a lot of short trips, low speed driving will not provide the exhaust system with a high sufficient temperature to start or complete a regeneration, so the filter can block up faster.
  • High Kilometre vehicles: As these vehicles with DPF systems age they will jump to show that filter regeneration is tougher to complete. Like any part on the car they do wear out and can no longer be mended.

Maintaining a DPF

A holistic approach needs to be adopted when considering care of your DPF system, meaning you need to look at the vehicle’s complete health when considering proper maintenance for your DPF. Here are a few items to consider about when it comes to engine issues in association to DPF plugging:

  • Air filters need to be inspected and replaced at the suggested intervals. A muddy air filter can lead to a smaller amount of air to the engine, and when the air-fuel ratio is not precise for the engine the result is improper combustion in the cylinders.
  • Worn fuel injectors cause engines to run rough, lose fuel economy and lead to improper combustion, which can cause filter plugging.
  • Your vehicle’s turbo charger and charge air cooler need to be tested for good operation as well. Turbochargers that do not yield adequate air or have leaking seals, can lead to oil and soot generation in the exhaust system, possibly damaging the DPF.
  • When your DPF regenerates, it deoxidizes the particulate matter, and the exhaust pressure impulses the ash to the end of the filter. Using the correct type of engine oil and checking your vehicle’s oil consumption is serious as well. An approved CJ-4 rated oil is suggested due to its low ash generating properties for any automobile with a DPF. If your vehicle is using too much oil it needs to be noticed to prevent possible damage to both your engine and your DPF system.

Proper engine maintenance is crucial to keep a DPF operating properly. After any engine repair your DPF should always be cleaned by a skilled technician by means of proper equipment and methods.

Types of DPF

  • Catalysed Diesel Particulate Filters

Customary Diesel Particulate Filter systems contain a filter material located in the exhaust designed to collect solid and liquid particulate matter emissions while letting the exhaust gases to pass through the ceramic walls. Catalyzed Diesel Particulate Filters (CDPF) are intended to achieve collection efficiencies of 90% or greater in terms of mass.

  • Ceramic Diesel Particulate Filters

These types of particulate filters need to be regenerated. Regeneration of a DPF is to eliminate accumulated soot/carbon. Two general methods are continuous and intermittent regeneration.

  • Coated Diesel Particulate Filter

CDPF system traps carbon deposits as they depart from the combustion system, stopping their release into the atmosphere. Under satisfactory conditions the system then cleans itself with a measured ‘burn-off’ process, thus providing a self-contained clean air system without the need for service upkeep. This system comprises of a ceramic filter body of around 4 liters volume attached behind the exhaust manifold plus a distinct regeneration support unit on the engine’s intake manifold.

Illegal to Remove

Driving with a DPF delete system on the road is illegal.  It’s that simple.  If you read the texts that comes with the pipe it will noticeably state “for off road use only”.  Without the DPF, the truck will not get an authorization on emissions test. The Government’s decision to actively apply the regulations regarding DPF removal are welcome, since they eliminate any possible doubt regarding the issue and means that a device intended to reduce pollution should function as it should.

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