Flow-Through and Wall-Flow Honeycomb Ceramics: Structure, Function, and Applications

In exhaust gas aftertreatment systems, honeycomb ceramic carriers are mainly divided into two types based on structural differences: flow-through and wall-flow. These two designs differ fundamentally in physical structure, working principle, and application scenarios.

Basic Structure

The straight-through carrier has a parallel channel structure with open ends. All channels remain unobstructed from inlet to outlet, allowing exhaust gas to pass through the carrier in a straight path, with catalytic reaction occurring only at the channel walls.

The wall-flow carrier employs an alternating blocking design, where one end of adjacent channels is blocked, while the other end remains open. This structure forces exhaust gas to pass through the porous ceramic walls between the channels to exit the system, thus achieving a physical filtration function.

Working Principle

The main function of the straight-through carrier is to provide a catalytic reaction site. When exhaust gas passes through, gaseous pollutants (such as carbon monoxide, hydrocarbons, and nitrogen oxides) come into contact with the catalyst coated on the channel walls and undergo a chemical reaction, transforming into harmless substances. Its design focuses on maximizing the catalytic reaction surface area while minimizing airflow resistance.

The core function of wall-flow carriers is particulate matter capture. After exhaust gas enters the open inlet channel, it must be forced through the porous ceramic wall into the adjacent outlet channel due to the blocked outlet end. During this process, solid particulate matter (such as soot) in the exhaust gas is trapped within or on the surface of the channel wall, achieving physical separation.

Performance Parameter Focus

For straight-through carriers, key parameters include:

Porosity: determines the effective catalytic surface area per unit volume

Wall thickness: affects the carrier's heat capacity and mechanical strength

Coefficient of thermal expansion: reflects the material's dimensional stability under temperature changes

For wall-flow carriers, key parameters include:

Porosity and pore size distribution: determine filtration efficiency and airflow resistance characteristics

Ash capacity: affects maintenance cycle and service life

Thermal conductivity and heat capacity: affect temperature control during regeneration

Manufacturing Process Differences

The core of manufacturing straight-through carriers lies in ensuring precise channel dimensions, uniform wall thickness, and providing suitable surface properties for subsequent catalyst coating. Key process aspects include extrusion die precision control and sintering deformation management.

The manufacturing of wall-flow carriers requires additional alternating sealing processes and strict control over the microstructure of the porous ceramic body. The high-temperature resistance of the sealing material and the uniformity of the sealing depth directly affect filtration efficiency and durability.

Application Scenarios

Straight-through carriers are mainly used in:

Gasoline vehicle three-way catalytic converters (treating CO, HC, NOx)

Diesel vehicle oxidation catalysts (treating CO, HC)

Selective catalytic reduction system carriers (treating NOx)

Industrial waste gas catalytic purification devices

Wall-flow carriers are mainly used in:

Diesel particulate filters (capturing soot particles)

Gasoline particulate filters (capturing fine particulate matter)

Industrial flue gas pre-filtration systems

Summary

Modern emission control systems often combine two carrier technologies. For example, diesel vehicle aftertreatment systems typically employ a "DOC (straight-through) + DPF (wall-flow) + SCR (straight-through)" layout to treat different forms of pollutants. Straight-through supports aim for thinner walls and higher pore density to improve catalytic efficiency; wall-flow supports, on the other hand, improve filtration efficiency and regeneration reliability by optimizing pore structure and material formulation. We are a Chinese manufacturer of honeycomb ceramics. For more information, please contact us via email at annayu@169chem.net or WhatsApp at +8618909016373.