Diesel Particulate Filters (DPF) Knowledge All Here

What is Diesel particulate filter ?

Diesel Particulate Filters (DPF) are devices that physically capture diesel particulates to prevent their release to the atmosphere. Diesel particulate filter materials have been developed that show impressive filtration efficiencies, in excess of 90%, as well as good mechanical and thermal durability. Diesel particulate filters have become the most effective technology for the control of diesel particulate emissions—including particle mass and numbers with high efficiencies.

How Diesel Particulate Filters Work

With any filter, they ‘filter’ or trap particles, in this case harmful diesel exhaust soot particles, so they have to be emptied regularly to maintain performance. The DPF needs to be cleaned regularly, through a process called regeneration. During regeneration—either active, passive or forced regeneration—the accumulated soot is burnt off at high temperature (around 600°C) to leave only a residue of ash, effectively renewing or regenerating the filter, ready to take on more pollution from the engine.

Regeneration of Diesel Particulate Filters Diesel Particulate Filters (DPF)

Have high efficiency on dust grain filtration, up to 60%∼90%. During filtering, the accumulation of particles in the particulate filter will lead to diesel engine back pressure rise. When the diesel engine pressure reaches 16 kPa∼20 kPa, the diesel engine performance begins to deteriorate. Therefore, we need to clean particles regularly to restore the DPF working state, which is called DPF regeneration.

The biggest challenge of DPF is the regeneration problem. Particulate filter regeneration primarily involves particulate oxidation. Key elements for particulate oxidation include high temperature, oxygen, and oxidation time. However, diesel engine exhaust temperatures are generally less than 500℃, and in some buses, exhaust temperatures are even below 300℃. The key problem of particle filter regeneration is to reduce the equilibrium point temperature where particle formation and oxidation rates are equal. When back pressure is relatively constant, the system is in equilibrium. The balance point temperature is influenced by flow rate, particle composition, NOx content, sulfur concentration, charcoal formation, and engine fuel parameters.

Diesel particulate filter clean types:

There are two types of regeneration: active and passive.

DPF Active Regeneration:

Active Diesel Particulate Filter regeneration methods include burner fuel injection heating regeneration, electric heating regeneration, microwave heating regeneration, and infrared heating regeneration.

Burner fuel injection heating regeneration:

A burner is installed at the inlet of the particulate filter to inject diesel and secondary air, burning the charcoal particles in the particulate filter to regenerate. This method requires additional fuel and a constant burner temperature, necessitating an automatic adjustment control system to regulate fuel and secondary air supply values. During regeneration, rapid acceleration should be avoided, as it can extinguish the burner flame, causing incomplete combustion and resulting in white smoke emission from the vehicle.

Electric heating regeneration

This method involves electrically heating the particle filter to promote soot particle burning. Although it avoids smoke emissions, it demands high energy, posing challenges for small and medium power diesel engines. Additionally, uneven heating can cause non-uniform regeneration, potentially overheating and damaging the filter.

Microwave heating regeneration

Microwave heating uses unique selective and volumetric heating characteristics to form a spatial heat source within the filter, heating the carbon particles directly. This method employs electromagnetic waves to transfer energy efficiently. Key technology includes controlling the soot particles’ burning temperature to prevent filter damage from high temperatures.

Infrared heating regeneration

Infrared radiation heating selectively heats the filter body directly, reducing the time to reach the required temperature and lowering energy consumption. It provides high efficiency and a suitable temperature gradient for honeycomb ceramic regeneration. The advantages stem from its mechanism, where the filter material absorbs infrared energy, enhancing molecular movement and heating efficiency.

DPF Passive Regeneration

Common passive regeneration methods include the fuel additive catalytic regeneration filter system, CRT (Continuous Regeneration Trap) system, and CCRT (Catalyzed Continuous Regeneration Trap) system.

Fuel Additive Catalytic regeneration

This system uses a fuel-soluble catalyst that enters the exhaust after combustion and mixes with particles. The catalyst reduces the particle regeneration temperature, promoting effective cleaning.

CRT System

The CRT system includes an oxidizer (DOC) and a non-catalytic particulate trap (DPF). Diesel exhaust passes through the DOC, where CO and HC oxidize into CO2 and water, while NO converts to NO2. NO2 then oxidizes the soot particles, achieving regeneration and reducing emissions.

CCRT system

The CCRT system also uses an oxidizer (DOC) and a particulate trap (DPF) but includes a catalytic coating on the DPF. This allows NO produced in the DOC to continue converting to NO2 in the trap, ensuring complete soot oxidation. The CCRT system offers easier regeneration at lower exhaust temperatures and lower NOx/PM ratios.