Particle Emissions of Train Brakes

Abstract

Inhalable particulate matter concentrations have been found to reach concerning levels in underground subway stations around the world. Brake particles have been identified as a significant contributor to these elevated levels. However, there is still limited research into the effect of the braking behaviour of trains on the emissions of brake wear particles. The present thesis examines the influence of sliding speed and contact pressure on the airborne particle emissions of a high-speed train brake material. Twelve different sliding speed and contact pressure combinations were defined and tested using a copper-based brake pad and forged steel disc material in a pin-on-disc configuration. The coefficient of friction (COF), temperature and particle number concentrations and size distribution were recorded over time. The results are presented in the form of sliding speed-contact pressure maps, which enable the dependence of the results on these variables to be visualised and discussed. Furthermore, the mass loss of the components was recorded. A correlation between the COF, temperature, wear mass loss, particle number concentration (PNC) and size distribution and the sliding speed and contact pressure could be identified. In order to gain deeper insights into the potential health impacts of the emitted particles, particles were collected for offline analysis with the objective of assessing their composition and particle toxicity. The results of the cell exposure tests indicated that the collected wear particles exhibit cytotoxic effects, which underscores the importance of further research into the reduction of brake wear particle emissions. Finally, the findings were evaluated with respect to their applicability for identifying an effective braking strategy in real-life train operations with the objective of reducing airborne wear particle emissions and minimizing adverse effects on human health and the environment.

Popular Abstract

The inhalation of airborne particles in urban environments and subway stations has been a cause of concern since the potential negative effects on human health are not yet fully understood. In order to minimize these effects, it is necessary to reduce the levels of airborne particles. When commuters are waiting on the platform for the train, a significant proportion of the particles they are exposed to originate from the wear particles produced by contact between the brake pad and brake disc of the train. The number of suspended particles in the air is dependent on a number of factors, including the braking conditions. These include the speed of the train when braking and the severity of the braking, which is the pressure level at which the brake pad is pressed on the brake disc. Twelve different combinations of sliding speed and contact pressure were tested in an experimental setup to propose braking conditions that minimize particulate emissions into the air. This pin-on-disc setup consists of a horizontal rotating disc made from the material of a high-speed train brake disc and a pin which is pressed onto the disc from the top and manufactured from a train brake pad. Since the setup is placed in an enclosure and clean air is blown through, the particles that become suspended in the air can be detected by particle sampling instruments which are connected to the outlet. A correlation was identified between sliding speed and pressure and the wear, friction, and particle emissions. Further, the number of airborne particles was found to be the highest at high sliding speed and pressure. However, the many interacting factors such as temperature, wear behavior and material composition limit the generalizability of the results and recommended braking pattern.

To determine whether the conditions under which particle emissions are minimal are beneficial, the particle toxicity was examined. This was accomplished by exposing lab-cultured human lung cells to particles collected on quartz filters within the same experimental setup. The toxicity was assessed by the number of cells that died over an exposure time of 24 hours. The filter material was observed to be toxic to the cells at high concentrations. At lower concentrations, however, cell death appears to be due to the toxicity of the particles. It was therefore concluded that the particles seem to have toxic potential for the cells, and there might be adverse health effects from particle exposure in subway stations. This highlights the necessity for further research into the reduction of particle emissions and particle toxicity.

• author: Tanzeglock, Leonie
• supervisor: Yezhe Lyu
• organization: Production and Materials Engineering
• course: MMTM05 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Non-exhaust emissions, High-speed trains, Copper-based brake pads, Pin-on-disc, Particle toxicity
• report number: LUTMDN/(TMMV-5361)/1-69/2024
• language: English
• id: 9159154
• date added to LUP: 2024-06-07 17:50:14
• date last changed: 2024-06-07 17:50:14