What is Diesel Particulate Filter (DPF) in a Car?
A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Diesel particulate matter is considered harmful to health when inhaled, so filters were introduced to remove this particulate matter from the exhaust gases of diesel-powered vehicles.
Modern diesel vehicles use a wall-flow particulate filter to trap the microscopic particles contained in diesel exhaust soot. As the particles build up, they begin restricting the filter, hence the need for regeneration (cleaning). The filter has a honeycomb structure that forces exhaust gases to flow through the porous walls, where the particles get trapped as the gases pass. The gases can then exit the filter but without the particulate matter.
How does a Diesel Particulate Filter Work?
A diesel particulate filter works by forcing engine exhaust gases to flow through a porous honeycomb medium (the filter) where the carbon soot particles get deposited on the walls of the filter while the cleaned exhaust gases are allowed to exit out the other end.
The filter has small pores large enough for gases to flow through but still small enough to trap most carbon particles and particulates from the engine. As these particles build up inside the filter, they form into a soot cake that collects even more particles even as it blocks part of the filter, hence the need for regeneration.
During regeneration, the high temperatures burn off the particles, converting them into less harmful components restoring the DPF to normal operation. Regeneration can either happen passively or actively depending on various factors.
Components of Diesel Particulate Filter
The main component of a modern DPF is a wall-flow filter block made from a porous ceramic material. It features an internal honeycomb structure with several small parallel channels running from one end to the other.
The channels are alternatively plugged at each end, forcing the exhaust gases to flow into one channel and out through the porous walls into the adjacent channel. Other components include:
Inlet and outlet pipes
A silicon carbide or cordierite substrate
Catalyst coating of substances like platinum or ceria
Catalytic converter to help with regeneration
Electronic control unit to monitor filter status
Importance of DPF in Diesel Engines
There are several important reasons why the diesel particulate filter was introduced in diesel engines:
Reduces Environmental Pollution- The particulate matter from diesel exhaust contributes significantly to air pollution and smog formation. DPFs help reduce emissions from diesel cars by 85%, making them less harmful.
Health Reasons– The microscopic soot particles in diesel exhaust are small enough to penetrate the lungs, causing respiratory diseases. Removing them improves health outcomes related to diesel exhaust.
Compliance with Emission Regulations– Rules such as BS 6 emission regulations make DPFs mandatory for all new diesel cars as part of efforts to reduce air pollution from vehicles.
Improves Engine Efficiency– Reducing particulate emissions enables diesel engines to burn fuel more efficiently, which increases performance, particularly torque and power output.
Allows Use of Low Sulphur Fuel– DPF technology works optimally with ultra-low sulphur diesel fuels, so its adoption has facilitated the supply and use of cleaner diesel fuels.
Therefore, although the DPF system increases the cost of diesel vehicles, its emission reduction and health benefits make it an indispensable component of all modern diesel-powered cars and trucks.
Signs of a Blocked Diesel Particulate Filter
Some key indicators that your DPF might be clogged include:
Reduced Engine Power and Performance- The engine may feel underpowered, especially when accelerating or going up gradients. Fuel consumption may also increase noticeably.
Warning Lights- A blocked DPF will trigger warning lights on the dashboard, such as the engine check light. Drivers should not ignore such warnings.
Excessive Exhaust Smoke- More white or black smoke than normal is emitted, indicating issues with combustion or the DPF.
Increased Regeneration Frequency- If regeneration starts occurring more often, it shows soot build-up is rising faster, indicating a failing filter substrate.
Strange Exhaust Noises- Unusual exhaust sounds like rattling or metallic noises can signify internal DPF damage or other issues needing repair.
Prompt diagnosis of these symptoms is vital to prevent further damage to the DPF system or the engine itself. Software updates may restore normal operation, but physical repair or replacement may be needed in severe cases of filter clogging.
Tips to Maintain a Diesel Particulate Filter
Proper diesel particulate filter maintenance is key to its efficient operation. Here are some useful maintenance tips:
1. Use Recommended Fuel and Oils- Ensure ultra-low Sulphur diesel is used and oils meet specifications for DPF use. Avoid fuel contamination at all costs.
2. Drive at Optimal Engine Temperatures- Avoid extensive engine idling and cold starts. Also, take cars at highway speeds regularly to allow exhaust gases to get hot enough for ideal DPF regeneration.
3. Follow the Manufacturers Service Schedule- Stick to prescribed intervals for oil changes, filter checks and cleaning to prevent premature DPF failures.
4. Avoid Short Trips Where Possible- Short drives prevent exhaust systems from getting hot enough to regenerate DPF systems effectively. Combine trips if feasible or occasionally take longer higher speed drives sufficient for self-cleaning.
5. Use Cleaner Fuel Additives- Reputable fuel additives help keep injectors clean, improve combustion and may reduce particulate emissions, hence lessening DPF clogging. However, avoid excess use of such products.
Passive DPF Regeneration
Passive regeneration relies on the natural process where occasionally elevated exhaust temperatures help burn off collected diesel soot when driving at optimal highway speeds. It requires no special actions since suitable temperatures are attained in due course.
Passive regeneration works thanks to a catalyst formulation coated onto the filter. The catalyst reduces the soot burn-off temperature to within reach of normal engine exhaust temperatures. This facilitates self-cleaning during regular vehicle use.
Active DPF Regeneration
Active regeneration engages when exhaust gas temperatures are insufficient to enable passive regeneration. It uses additional heat to clean off accumulated engine soot.
There are two main types of active DPF regeneration systems used:
Oxidation Catalyst Regeneration
This uses an extra fuel-borne catalyst (FBC) upstream of the DPF unit. Diesel fuel additives containing cerium or iron compounds act as extra catalysts to promote exothermic chemical reactions that raise temperatures. The heat generated and engine control modifications by ECU facilitate DPF regeneration.
Post-Injection Regeneration
After normal combustion events are complete, extra fuel is injected as a late second injection phase. This unburnt fuel oxidises in the DPF, releasing heat to incinerate collected soot. Precise timing and controlled conditions prevent adverse impacts of this excess fueling.
The engine management computer initiates active regeneration when needed without driver input. Warning lights inform drivers once the process is underway. Regeneration could last up to 30 minutes if carbon soot levels were high.
Conclusion
Diesel particulate filters are indispensable in trapping the microscopic soot particles contained in diesel exhaust gases. This protects human health and the environment from tons of pollutants emitted by ever-growing diesel-powered vehicular traffic worldwide.
Despite their extra costs and maintenance needs, DPF systems now ensure modern diesel vehicles have reduced their particulate emissions footprint by over 80%. Passive and active regeneration processes help facilitate efficient filter operation over hundreds of thousands of miles without needing replacement. These make diesel cars equipped with DPFs a safe and clean technology for drivers and society.
Frequently Asked Questions
