Source: Empa announcement
DÜBENDORF, Switzerland – The broad introduction of particle filters reduced the emission of combustion-generated fine and ultrafine particles significantly. As a result, brake disc and tire abrasion are moving into the focus of public health experts and engineers, given their health harming potential. There is still a major challenge, though: How can the quantity and size of brake dust particles be measured correctly? Empa, the Swiss Federal Laboratories for Materials Science and Technology, researchers are currently developing a sophisticated method to do the measurements.
The VW Jetta Hybrid on the chassis dynamometer in Empa’s Automotive Powertrains Technologies Laboratory had a couple of years of duty as a fleet vehicle. Strapped into the test chamber, it has been part of a new research purpose since July 2020: The goal is to generate brake dust, strictly following the standardized WLTP driving cycle, is the cycle that is also used to determine exhaust emissions.
Brake Dust Impact on Non-Exhaust Pollution
The interest in brake dust measurements is fairly recent: In June 2016, a department of the UN Economic Commission for Europe (UNECE) known as the “Particle Measurement Programme Informal Working Group” (PMP IWG) decided that it was time to develop a generally applicable test procedure for brake dust that would reliably determine the mass and the number of the emitted particles.
Since then, a number of research institutions, vehicle manufacturers and specialized companies for testing equipment have addressed the topic. However, there some severe challenges to tackle.
Unlike an exhaust pipe, which reliably emits gases in a given direction, a rotating brake disc distributes the particles in all possible directions. So you first have to collect the particles and then introduce them in a well-defined flow towards a particle analyzer. During this process losses have to be minimized: Neither fine particles should be escape, nor should coarse particles remain in the pipes.
Two further complications arise: The brakes of a vehicle are attached to a rotating drive shaft, which must be carefully sealed for the measurement so that no particles are lost. In parallel brakes have to be cooled.
On the road, the airstream together with ventilation lamellas inside the brake disks provide a cooling breeze. A fully enclosed brake on a test bench, by contrast, can heat up quickly – and would then yield completely different particles than in real everyday traffic. Such an analysis would thus be of little value.
The UNECE’s PMP IWG working group solves the problem by simplification: The desired brake tests are to be carried-out in completely enclosed test stands. Such test stands exist. They resemble large cabinets, in which brake discs and brake pads rub against each other. Only one component is tested, not the entire car.
“We are going to try out another way,” says Panayotis Dimopoulos Eggenschwiler, who is designing the test setup at Empa. “We want to measure all emissions of a vehicle simultaneously during a test drive on the chassis dynamometer. This is much more meaningful than data from an isolated brake tester, which must then be converted to real-world conditions.”
Together with Daniel Schreiber, an engineer by training, Dimopoulos Eggenschwiler has developed the Empa version of the test, the results of which must now stand up to comparison with other international research teams.
At Empa an entire vehicle is being tested, the VW Jetta Hybrid mentioned above.
The extensive post, including a number of images, can be viewed by clicking HERE.