HJS City-Filter® - Technology & how it works

With its unique design and materials, the City-Filter® offers major advantages over conventional particulate reduction systems. The robust design, extreme heat resistance and very high soot-holding capacity provide the ideal basis for retrofitting diesel vehicles. The HJS City-Filter® is maintenance-free and will last for the lifetime of the vehicle. It requires neither sensors, electronics nor additives.

The City-Filter® has been tested in Germany by TÜV and has the national type approval required under EU regulations. The filter is available for more than 800 different vehicle models.

HJS City-Filter® - How the filter works

How the filter works

The hot exhaust gases from the engine – which contain soot particles – are fed into the filter housing and through the sintered metal filter (SMF®) developed by HJS. The gaseous components flow through the microscopic pores of the filter pockets; the soot particles, including the ultra- fine particles, are trapped on the surface and deposited on the individual filter pockets.

Filter regeneration

Regeneration (cleaning) of the filter starts when the exhaust gas temperature reaches roughly 200°C. The nitrogen dioxide (NO2) formed with the help of the oxidation catalytic converter (aka oxi-cat) comes into contact with the soot deposited on the filter pockets, causing the soot particles to oxidise and degrade; the NO2 is then reduced to nitrogen oxide (NO). This chemical process is repeated continuously so that the HJS City-Filter® regenerates itself continuously, requiring no additional regeneration aids, such as assistance from the engine management system.

Combi system

HJS City-Filter® - Combi system

The HJS City-Filter® combi system consists of an integral oxidation catalytic converter (oxi-cat) or has a highly efficient catalytic coating, and ensures optimum regeneration when the necessary exhaust gas temperature is reached.

The combi filter also helps many car owners save money if they are forced by regulations to replace the oxi-cat of their car when retrofitting a particulate filter. This is because the relevant regulations stipulate that the oxi-cat already installed in the car may be no more than 5 years old or have covered no more than 80,000 km (50,000 miles). With HJS combi systems, a new oxi-cat or the catalytic coating is included in the price.

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