Diesel Particle Filter (DPF)

While diesel engines emit considerably less pollutant CO and NOx as well as green house gas CO2, the only shortcoming is excessive level of particles.

These particles are mainly composed of carbon and hydrocarbons. They lead to dark smoke and smog which is very crucial to air quality of urban area, if not to the ecology system of our planet.

Since the '80s particle emissions from cars have been reduced by three-quarters, thanks to the Government’s legislation as well as the advances in diesel technology such as direct injection. However, diesel engines still emit more particles than petrol, and it seems that it is the nature of diesel.

Therefore the largest diesel car maker, PSA, developed in 2000 a particle filter for HDi common-rail diesel family.

Basically, PSA’s particle filter (PF) is a porous silicon carbide unit, comprising passageways which has a property easily trap and retain particles from the exhaust gas flow. Before the filter surface is fully occupied, these carbon / hydrocarbon particles should be burnt up, becoming CO2 and water and leave the filter accompany with exhaust gas flow.

This process is known as regeneration.
Normally regeneration takes place at 550° C. However, the main problem is that this temperature is not obtainable under normal conditions. PSA tells that normally the temperature varies between 150° and 200°C when the car is driving in town, as the exhaust gas is not in full flow.

Luckily, the new common-rail injection technology helps solving this problem. Gifted by its high-pressure, precise injection during a very short period, the common-rail system can introduce a post-combustion by injecting small amount of fuel during expansion phase. This increases the exhaust flow temperature to around 350°C.

Then, a specially designed oxidising catalyst converter locating near the entrance of the particle filter unit will combust the remaining unburnt fuel come from the post-combustion. This raise the temperature further to 450° C.

The PF unit needs to be cleaned at dealerships every 80,000 km by high-pressure water, to get rid of the deposits resulting from the additive. Modern PF are cleaning while you drive your car by a controled overheating of the entire PF to eliminate the particles stocked.


Author: AL
Source: Autolatest & AZ