Fact sheetExhaust filter FL

CRT

Volvo’s exhaust filters work as both silencers and exhaustgas cleaners and are intended for vehicles operating in asensitive urban environment with heavy traffic.

The Volvo CRT (Continuously Regenerating Trap) filteris matched to the Volvo FL 6-litre engine. The exhaustfilter reduces emissions of health-affecting substances inthe exhaust gases – carbon monoxide, hydrocarbon andparticulates (microscopic soot particles) – by 80-90 %with no effect on engine power.The filter cleans the exhaust gases in two stages. First,carbon monoxide and hydrocarbons are reduced in acatalytic converter, then the particulates are trapped andburnt in a particulate filter.The exhaust filter is intended for vehicles that operate ina sensitive urban environment with heavy traffic, forexample goods distribution, refuse collection and localauthority service vehicles.The filter, which replaces the normal silencer, satisfiesthe requirements of current noise legislation for 78/80dB(A). Made from stainless steel, it is designed like aconventional silencer and installed in the same place.The sulphur content of the fuel used in vehicles with anexhaust filter must not exceed 50 ppm. Fuel with ahigher sulphur content results in increased exhaust back-pressure and high temperatures, which may destroy thefilter and possibly damage the engine.The filter cartridge must be removed and cleaned at everyoil change.When vehicles with an exhaust filter are being operatedindoors, good ventilation or exhaust extraction must beprovided in the same way as for vehicles without anexhaust filter.

Exhaust filter FL-CRT has the following distinguishingfeatures:• The entire silencer unit is made of stainless steel.• Catalytic converter with ceramic body coated with

catalytic material, including noble metals, whichoxidise large amounts of the substances that areharmful to health.

• The particulate filter is made from a porous ceramicmaterial, shaped to form channels. These channels trapthe particles, which are then burnt.

• The filter is kept clean by continuous oxidation of theparticles in the exhaust gases.

• Meets the same requirements as the conventionalsilencer, which it replaces.

Cutaway view of the cleaning process in the exhaust filter

2002-09-23 ENG Version 01

Fact sheetExhaust filter FL

CRT

Easy servicing and

minimal maintenance

Non-combustible particles (ash)must be blown out of the filter atevery oil change. The filter must bereversed during cleaning so that theair flows through the filter walls inthe opposite direction.

Two-stage process with

combustion of

particulates

The exhaust gases are cleaned in twostages. First, the gases pass through aceramic catalytic converter coated innoble metals. Here, 90 % of the carbonmonoxide is oxidised to form carbondioxide (CO2) and about 85 % of thehydrocarbons (HC) are converted intocarbon dioxide (CO2) and water vapour(H2O). Some of the nitric oxide (NO)is converted into nitrogen dioxide(NO2), which is used to facilitate thecombustion of soot particles in stage2.The process increases the emissions ofnitrogen dioxide to some extent, butthe total amount of oxides of nitrogenis unchanged. Moderateconcentrations of nitrogen dioxide maycause irritation of mucous membranesand the respiratory system, especiallyfor asthmatics.In the second stage the soot particlesare trapped in a particulate filter. Thisis a ceramic filter is made up ofchannels and filter walls with poresthat trap 80 % of the particles.The soot particles are thencontinuously burnt, forming carbondioxide and water vapour. Because ofthe hot gases, the combustion processis self-sustaining. It starts at a tempera-ture of about 275 °C. At lower tempe-ratures, for example when the engineload is low, the particles are not burnt.This is not a problem for short periods,but running an engine at idling formore than three hours is notrecommended.Overall, the filter offers major adv-antages in the form of reducedemissions of particulates,hydrocarbons and carbon monoxide,as well as the positive effects this hason the human health and theenvironment.

Fuel with a low-sulphur

content must be used

When the exhaust filter is fitted, adiesel fuel of the correct qualitymust be used. The sulphur content ofthe fuel must not exceed 50 ppm. Ifthe sulphur content of the fuel ishigher, the catalytic converter willproduce sulphur trioxide instead ofnitrogen dioxide. The soot particlesin the fuel will be unable to burn andwill quickly clog the particulatefilter.This leads to increased exhaust back-pressure and high temperatures,which destroy the filter and maydamage the engine.The availability of fuel with the cor-rect sulphur content variesthroughout Europe. In 2005, stricterregulations will come into force inthe EU, limiting the sulphur contentof the fuel to 50 ppm.

Combined silencer and

exhaust gas cleaner

The exhaust filter serves both as anexhaust gas cleaner and a silencer.The filter is installed in the sameplace as the silencer and can be retro-fitted.Only a few minor changes are neededwhen installing the filter. Theconnections between the exhaust pipeand the filter look the same as beforeand the options of having a vertical orside-outlet exhaust are still available.Externally, the only differencecompared with a conventionalsilencer is that the filter is made ofstainless steel.The installation has been thoroughlytested and satisfies the currentrequirements in terms of noise,geometry and pressure drop.The effect of the filter on engineperformance and fuel consumptionis minimal.The increase in weight when thefilter is installed is only 18 kg.

The exhaust filter is installed at the sameplace as a conventional silencer

The process reduces particulate emissions(PM) by about 80 %, carbon monoxide(CO) by about 90 % and hydrocarbons(HC) by about 85 %

Test outlet in filter body

The exhaust filter has a test outlet forchecking the exhaust gas back-pressure.

Principle of exhaust gas

cleaning

Stage 1

Catalytic converter

Stage 2

Particulate filter