Aerosol filtration in a wall flow filter

Understanding catalytic filter devices for automotive emissions control

Particulate matter (PM) pollution remains a major public health concern. The installation of particulate filters on the exhaust of road vehicles with combustion engines has been critical in capturing PM before they pollute the environment. 

However, the deposits cause the permeability of the filter to change continuously, and over time, without remediation, it can lead to excessive back‑pressure from the exhaust, lowering the fuel efficiency of the engine and increasing greenhouse emissions.

The challenge

It is critical to understand filter trapping and the 3D distribution of particulate emission in a wall flow filter in order to better control the processes involved. 

Understanding the effects of pore scale structural changes in particulate filters, how deposits restrict flow through the filter, and how they can be efficiently burnt off is currently an ongoing challenge, in particular with constantly tightening emissions legislation  

A high‑resolution non‑destructive technique was needed to monitor these processes occurring within the particulate filter in greater detail and over time.

The benefits

With access to new insights into the mechanisms by which filter efficiency and pressure loss can be affected in service, the concentration of PM output from the exhaust and the fuel efficiency of the vehicle power unit can be better estimated. 

This approach can be directly applied to catalyst‑coated automotive wall flow filters to dynamically image the interface between the soot‑like deposits and the catalyst layer. This knowledge can contribute to real‑world improvements in clean air technology and public health.

Moreover, this methodology provides new opportunities for studying the mechanisms by which filter efficiency and pressure loss can be affected by aerosols, and may find additional use for HVAC and PPE applications.