Brake Particle Emissions From Freight Trains

Abstract

This research has been conducted to measure the brake particle emission from freight trains drag braking operation. It only focuses on mechanical brakes by using two different brake pad material one is sintered, and another one is composite, in combination with grey cast iron brake disc. All the materials have been collected from real time braking operations from Green cargo. This research is an example of a joint collaboration within academia and industry. Lund university performs as the academic partner and Green Cargo ab has been the logistics and finance contributor for this study.

This experimental work was conducted using a pin-on-disc tribometer under controlled laboratory conditions. Particle number concentration and size distributions were measured by using a condensation particle counter (CPC) and a mini wide-range aerosol spectrometer (MiniWRAS). In this study a K-type thermocouple has been installed in the disc of the pin-on-disc tribometer to monitor the surface temperature of the sliding operation between the friction materials. The wear mechanism and surface morphology of the tested pads were investigated using scanning electron microscopy (SEM) and material characterization was done by energy-dispersive X-ray spectroscopy (EDXS).

The results showed that sintered pads indicate more stable friction and temperature increase in the repeated drag braking than composite pads. The wear rate of sintered pad is 34% higher than composite pad, which also showcasing the stability of CoF of the sintered pad. Both brake pads show almost similar particle number concentration in the repeated drag braking tests, whilst sintered pads have doubled PM10 than composite pads in the repeated drag braking tests.

Sintered pads showcase wider mass-weighted size distribution and coarser particle sizes than composite pads in the drag braking runs. While the mass concentration of PM2.5 for sintered pad is slightly higher than the composite pad material. Worn surfaces of sintered pads are mainly composited of metallic elements whilst composite pads exhibited a certain amount of non-metallic elements besides metals on their worn surfaces.

This research contributes valuable insights to the understanding of non-exhaust emissions from rail transport and supports future efforts toward greener and safer braking technologies in alignment with EU sustainability goals.

Popular Abstract

Freight trains are well known for their lower CO2 emissions, greater energy efficiency and cost effectiveness. This makes this transport popular over other vehicles for transporting goods. But while trains don’t produce exhaust like cars or planes, they still release harmful particles into the air, especially when braking. These particles are tiny, often invisible to the eye, and can travel deep into our lungs, potentially causing serious health problems.
In my thesis, I studied two types of brake pads used in freight trains mechanical braking system, one is sintered pad and another is composite pad. I wanted to find out which one wear slower and releases fewer harmful particles during braking. Using a lab setup that represented real train braking, I measured how much material each pad lost, how many particles were released in terms of number and mass, and how stable the braking was. I also did microscopy analysis for both the pad surface that was used in the lab to show the variation in surface wear between two pads.
The results showed a trade-off between particle emission and braking ability. Sintered pads presented more stable braking but released more particles than composite pad in case of particle number as well as particle mass. Composite pads, on the other hand, wore down more slowly and emitted fewer particles. But Composite pad braking efficiency was not stable, and it also raises higher temperature while braking than sintered pad.
Based on the results of this study, the choice of brake pad material depends on the main target of the user. If the aim is to reduce air pollution and limit the emission of harmful particles, then composite pads are a better option. They produce comparatively less PM₁₀ and PM₂.₅ particles and have a lower wear rate than sintered one. However, if the main focus is on braking performance and friction stability, especially during repeated braking, then sintered pads are more suitable, as they provide more stable braking but at the cost of higher wear and more coarse particle emissions. Overall, for environmental benefits and longer material life, composite pads are recommended over sintered pad.

• author: Monica, Maksuda Aktar Kalam
• supervisor: Yezhe Lyu
• organization: Production and Materials Engineering
• course: MMTM05 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Non-exhaust emissions, Freight trains, Sintered brake pads, Composite brake Pad, Pin-on-disc, Particle number concentration, Particle mass concentration, Mechanical train brake, Scanning electron microscopy.
• report number: LUTMDN/(TMMV-5376)/1-60/2025
• language: English
• id: 9198860
• date added to LUP: 2025-06-13 15:09:28
• date last changed: 2025-06-13 15:09:28