How to improve emissions caused by older diesel cars

Tackling the issue of the legacy fleet of older diesel vehicles will help speed up efforts to make Europe’s air cleaner.

In 2015, diesel vehicles made up 42 percent of the total fleet of passenger vehicles in the EU. Although new Euro 6d-temp vehicles meet current emissions standards, the older diesel vehicles that remain on the roads continue to have an important impact on air pollution. Some cities are introducing access restrictions to the older, more polluting vehicles. So, what are the options for owners of older diesel vehicles?

As EU Member States regularly surpass EU NO2 limits, reducing pollutant emissions from diesel vehicles has been an area of particular interest for policymakers. We take a look at scrapping schemes and retrofitting options as ways to accelerate the reduction of emissions from older diesel vehicles.

 

How do scrapping schemes work?

Scrapping schemes are necessary to accelerate the replacement of older diesel vehicles and meet emission reduction goals.

Scrapping schemes encourage drivers of older diesels to switch their car or van to a more environmentally friendly vehicle, such as a Euro 6d-temp diesel, through many incentives, such as compensation, part-exchange or fiscal benefit.

An example of a successful scrapping scheme is the French “prime à la casse” system where drivers of old diesel cars receive a compensation of up to €2,000 when switching to new diesel vehicles. Since January 2018, this initiative has already helped to replace 60,000 vehicles in France. Several car manufacturers are offering such schemes across Europe as well.

Accelerating the scrapping of old vehicles and replacing them with Euro 6d-temp vehicles which meet the latest emission standards is an efficient answer to tightening air quality standards and emission reduction regulation in cities.

Scrapping schemes and retrofitting are steps to rapidly improving air quality, health and mitigating the environmental impact in Europe.

How does retrofitting older diesels work?

A key development in preventing harmful emissions has been the Diesel Particulate Filter (DPF), which traps soot particles. All new diesel cars in the EU have been fitted with this technology since 2011. However, technologies to reduce nitrogen oxide (NOx) emissions have been broadly introduced only later.

Retrofitting older diesel vehicles with systems that reduce NOx exhaust emissions is a viable solution to today’s air pollution challenge, with some options reducing emissions by up to 70%.

Selective Catalytic Reduction (SCR) systems are seen as an efficient technology necessary to achieving emission standards. They work by adding ammonia – either in the form of AdBlue®, a liquid NOx reducing agent, or directly as a gas, using cartridges – to the exhaust gases. This then reacts in a catalytic converter with the nitrogen oxides coming from the diesel engine to release harmless nitrogen and water vapour at the tailpipe.

 

What are the challenges of retrofitting diesel vehicles?

Retrofitting is a potential measure for reducing emissions from older diesel vehicles and improving urban air quality. It has proven very effective with heavy-duty trucks and buses as well as construction machinery. However, for passenger cars it is not without challenges:

  • SCR systems can be complex and costly to install, with costs of purchase and installation ranging from €1,400 to €3,300, more likely in the upper third of this range, according to the German motor club (ADAC) investigations.
  • Where ammonia passes through the SCR without reacting, ammonia slips can occur. This can be easily prevented by a slip catalyst, but it needs to be carefully designed.
  • Insufficient vehicle space can also be a challenge. Many vehicles that could be retrofitted do not have enough room to integrate the SCR catalytic converter into the exhaust system.
  • The adequate storage of AdBlue® or ammonia may also pose an issue. It requires a separate tank, which is usually installed in the spare wheel well.

Producers of retrofitting technology stress the importance of close involvement and cooperation with the original vehicle manufacturer and support from dealer networks for distribution, installation and periodic emissions testing.

These complications must all be taken into consideration but can vary depending on the vehicle and amount of driving. Despite the challenges, retrofitting is an effective way of reducing NOx emissions from older diesel vehicles.

 

The need for effective retrofitting standards

Currently there are no EU-wide guidelines on what to do with diesel vehicles that do not meet emission standards. While most cities in Europe have established Low Emission Zones (LEZs), in which higher emission-producing vehicles are restricted, a single solution has not yet been provided to address the fleet as a whole.

There are several technical and certification elements that policymakers must consider, so that the rush to find a solution does not impact the viability of retrofitting procedures and delivers the necessary benefits to urban air quality.

The difficulty for policymakers in considering all of these elements is that there is no one solution that works for all makes and models of vehicles.

Proactive solutions are needed now for the owners and operators of older diesel vehicles. Policymakers will be looking to address the current complexities in the automotive industry, and to set attainable solutions for consumers, dealers, manufacturers and Member States in the coming years.

When addressing the challenge of reducing emissions from older diesel vehicles, scrapping schemes and retrofitting are an important part of the solution and are useful to rapidly improving air quality, health and mitigating the environmental impact in Europe.