Reducing the nanoparticles generated at the wheel–rail contact by applying tap water lubricant at subway train operational velocities

Abstract

The formation characteristics and the reduction of nanoparticles emitted from wheel–rail contacts at subway-train velocities of 73, 90, and 113 km/h under dry and water-lubricated conditions (using tap water) were studied using a twin-disk rig. The resulting number concentration (NC) of ultrafine and fine particles increased with train velocity under both conditions. Particle generation varied with slip rate under both conditions in both the particle categories. Furthermore, the formation characteristics at 113 km/h under dry conditions showed a notable deviation from those under water-lubricated conditions in three aspects: (i) The maximum NC of ultrafine particles was higher than that of fine particles, (ii) the predominant peak diameter was in the ultrafine particles category, and (iii) the proportion of ultrafine particles was much higher than those of the fine particles. Applying water decreased the NC of ultrafine and fine particles significantly at all tested velocities (by 54–69% and 87–91%, respectively). Adding water increased the NC of particles ≤ 35 nm in diameter, possibly owing to the increase in water vapor and mineral crystals from tap water. Overall, this study provides a reference for researchers aiming to minimize nanoparticle formation at the wheel–rail contacts by applying a lubricant.

Effectiveness of Tap Water in Reducing the Generation of Ultrafine Wear Particles from the Wheel-Rail Contact by Eliminating the Water Vapor Effect

“…In this study, a newly developed small-sized twin-disk rig was utilized to investigate the generation of AWPs at the wheel-rail contacts. This rig was designed based on the twin-disk rig used in previous studies [1,2,27,[29][30][31]. Each disk was connected to a-45 kW AC motor and driven independently.…”

“…The experimental setup used to simulate the generation of AWPs at the wheel-rail contacts was described comprehensively in previous studies by Lee [1,2,27,[29][30][31]. The schematic of the experimental setup is shown in Figure 1.…”

“…As a continuation of the previous study [31], this research aimed to verify the effectiveness of tap water application in reducing the NC of nano-sized wear particles generation, especially ultrafine particles, by eliminating the influence of water vapor. To ensure an accurate assessment of the reduction in nano-sized wear particle generation at the wheel-rail contact, a diffusion dryer was employed to eliminate the effect of water vapor.…”

“…Lee [30] further reported that applying tap water at the wheel-rail contact significantly decreased the NC of fine wear particles and reduced micro-sized wear particles to nearly negligible levels across various train velocities. However, Lee's studies [29][30][31] were conducted under tap water conditions, showing an increase in particle NC of ≤35 nm in diameter, possibly due to water vapor and mineral crystals from tap water. However, these studies by Lee [29][30][31] did not utilize any form of dryer to remove water vapor generated at high contact temperature.…”

“…However, Lee's studies [29][30][31] were conducted under tap water conditions, showing an increase in particle NC of ≤35 nm in diameter, possibly due to water vapor and mineral crystals from tap water. However, these studies by Lee [29][30][31] did not utilize any form of dryer to remove water vapor generated at high contact temperature.…”