Particulate Emissions from Iron Brakes

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Source: Keronite post

HAVERHILL, U.K. — The automotive industry places a lot of focus on replacing heavier iron components with lightweight alternatives such as aluminum or carbon composite. This is especially true in high-performance vehicles for motorsport, where every kilogram counts. Recent research shows that iron brakes not only add unnecessary weight to a vehicle, but they’re also contributing to particulate emissions and air pollution.

Iron brake discs are commonly used across the automotive industry. They have been used for decades and are an established, cost-effective technology.  A robust supply chain system exists for iron brake discs in the automotive industry as the concept and design has hardly changed in over 50 years.

There are two main drawbacks to using iron brake discs in passenger vehicles. Firstly, they’re heavy. The main challenge for automotive engineers over the last few years has been to increase engine efficiency and reduce CO2 emissions. Reducing the weight of the vehicle will improve fuel economy and reduce running costs. As using electric and hybrid vehicles becomes more widespread, reducing vehicle weight will allow for a longer range, allowing for an increased travel distance on a single charge.

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The second issue with iron brake discs is particulate emissions. The cast iron brake discs of road vehicles are the main source of iron particulates affecting air quality. Usually, a car’s braking system is made of an iron brake disc and a high-friction polymer-based brake pad. Over time, we see significant wear to both the brake discs and brake pads, which leads to them being replaced to ensure passenger safety. Wear on brake discs and pads generates particulate matter which contributes to air pollution, something which continues for the entirety of a car’s useful life.

Particulate matter from traffic

Exhaust emissions have long been recognized as a contributor to air pollution. There is legislation in place which requires car manufacturers to ensure vehicles remain below specified levels of carbon monoxide, nitrogen oxides, hydrocarbon, and particulate matter emissions.

Although many studies on air pollution focus on exhaust emissions from traffic, there has been more recent research that shows that small solid particles constitute a significant proportion of non-exhaust particulate matter. Studies show that, since exhaust filters have improved, particulate matter originating from brake wear, tire wear and road surface wear now makes up a significant proportion of particle pollution in the air.

A report from the U.K. Government’s Air Quality Expert Group highlighted the problem of non-exhaust particulate matter to Environment Minister Therese Coffey in 2019. She commented that, “It is not just fumes from car exhaust pipes that have a detrimental impact on human health, but also the tiny particles released from their brakes and tires.”

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However, there is currently no legislation in place to restrict non-exhaust emissions from passenger vehicles. Particulate matter levels are difficult to measure, and it is also difficult to identify the source. Independent testing company Emissions Analytics carried out real-world testing to measure tire wear. They found that a typical family hatchback emitted approximately 5.8 g/km of particulate matter. Compare this to 4.5 mg/km of permitted exhaust emissions and we can see that particulate emissions from tire, brake and road wear pose a considerable threat to air quality.

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