Technical inspection to tackle particle filter fraud from July 1st

From 1 July, the emission measurement for diesel cars in the Belgian annual technical inspection will be changed. From then on, diesel cars will have to pass a new test procedure to map out the emission of particulate matter in the exhaust gases.

The new system counts the particles that are present, making it possible to measure more accurately and, above all, detect the efficient operation of a soot filter and expose frauds that removed the filter completely and had the unit welded shut.

Existing test is outdated

The new test procedure was introduced after it became clear that the existing measurement method at the technical inspection was outdated. Until now, measurement occurred using an opacity test prescribed by the European directive.

Under the impulse of Flemish minister Lydia Peters (Open Vld) and Brussels minister Elke Van den Brandt (Green), Belgium is going a step further with a new test. Until now, only the transparency of the exhaust gases was measured.

On one side of the test cell, there is a light source, and on the other side, they measure the amount of light that passes through the exhaust gases (in the cell). Based on that percentage, a car was considered good or bad. In practice, only vehicles that smoked black were detected.

The second disadvantage of the measurement method was that the diesel engine was driven to its maximum revolutions per minute during the test. This procedure was criticized from the outset because it is detrimental to the engines.

It’s also unhealthy for the employees, and has little relevance, as a diesel engine runs at around 2 000 revolutions under normal circumstances and will rarely exceed 3 500 revolutions on public roads.

Fighting fraud by counting particles

One of the side effects of the old measurement method was that little could be learned from the test about the actual emissions of the vehicles. Moreover, a car where the DPF filter was removed proved to pass the test easily.

Many customers do not wish to replace the expensive filter (which costs between 500 and 2 500 euros). The casing is then cut open, the contents removed, and the unit welded shut so that the empty filter housing is in place.

To tackle this, a renewed test will no longer measure the opacity but counts the number of particles per cubic cm. In addition, the test no longer takes place at high engine speeds; the engine will have to idle for 30 seconds.

Vehicles achieving less than 250 000 particles per cm3 are okay; if the value is between 250 000 and 1 million, a remark will follow, and corrective measures may be imposed.

Diesel engines that reach a value of over 1 million are immediately given a red card. In the first phase, the test is for diesel vehicles (passenger cars and light trucks) that meet the Euro 5 standard and above. Due to the stationary measurement, engines with chip tuning will also rarely or not be noticed. The only relevant measurement method would be a representative driving test on a roller dynamometer that also includes mild acceleration.

Good start, but NOx remains out of scope

The particle counter is a good first step, but it mainly says something about the presence of a particulate filter. The potential for fraud is much greater because, in addition to particulate filters, entire EGR systems are also removed.

Such systems ensure a controlled re-combustion of the exhaust gases to reduce the nitrogen oxides in the emissions. Unfortunately, the particle counter will not measure this fraud, although this very element was at the root of dieselgate.

NOx emissions are a concern not only in diesel engines but also in modern gasoline engines. The sensors that monitor this often break down and are expensive (over €500) to replace.

These systems are also increasingly being deactivated by adapting the software, because a NOx measurement is not an element of the inspection. This is remarkable because NOx emissions are under enormous pressure in other sectors lately, like energy and agriculture.


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