C5 Aircross Automatic Passive DPF Regens.

Faults and Technical chat for the Citroen Aircross
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Szeliga
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Post by Szeliga » Wed Jul 13, 2022 3:47 pm

I recently purchased a 2019 C5 Aircross 1.5 BlueHdi Automatic and noticed the car was performing regens every 170 miles. My driving is a mixture of town/motorway at a ratio of 60/40.

Can anybody tell me if this normal or on the low side? My previous car was a C4 Picasso BlueHdi1.6 hdi with regens every 400/500 mile intervals.

I use the FAP android app to monitor what is happening to the DPF’s soot, pressure levels etc. My C5 Aircross reaches 17.5 grams when the regen kicks in. It stops when the level drops to 3.5 grams.

Can any other C5 Aircross 1.5 BlueHdi owners offer any advice and help to put my mind at rest?

Thanks.

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Juan Sheet
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Post by Juan Sheet » Wed Jul 13, 2022 5:47 pm

Simply put the design of the 1.5 is such that the cat and the DPF are vertical and at the front of the engine and are combined into one unit with separate components inside. Your previous 1.6 Blue HDI was a different engine design and therefore had the catalytic converter at the front, but the particle filter was a lot larger and at the rear.

So basically the older DPF was a lot bigger, so took longer to clog up and consequently took longer between regens than the 1.5 engine with a smaller DPF that needs to regenerate more frequently.

It's all about getting more out of a smaller space, making everything more compact and saving money of course.
C3 Aircross Flair 1.5 Blue HDi
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Beanee687
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Post by Beanee687 » Wed Jul 13, 2022 9:17 pm

Thanks for the explanation Juan.
Does that mean that the regens use the same amount of fuel for the same range as the old design. Smaller more often but shorter burn period, compared to larger less often but longer burn period.
2020 C3 Aircross Flair 130 BHP EAT6.
White with Black roof and orange mirrors & roof bars

Szeliga
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Post by Szeliga » Wed Jul 13, 2022 11:20 pm

Thanks Juan Sheet for an extremely informative answer. Much appreciated.

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Juan Sheet
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Post by Juan Sheet » Thu Jul 14, 2022 8:32 am

I wouldn’t of thought so as having a smaller DPF, means there is less of a capacity (area) to regenerate, so shouldn’t need as long.

There are 2 types of regeneration, passive and assisted. Passive regeneration happens naturally when the exhaust gas temperature reaches about 550C degrees. This occurs most frequently during longer journeys at constant speeds, like motorway driving. Assisted regeneration kicks in when the conditions are not optimal, like on shorter stop and start journeys when the exhaust gasses don’t get hot enough.

Assisted regeneration uses the additive that is injected into the fuel tank whenever you top up with diesel to lower the temperature required to burn off the particulate matter to only 450C degrees.
C3 Aircross Flair 1.5 Blue HDi
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Beanee687
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Post by Beanee687 » Thu Jul 14, 2022 10:27 am

Cheers for clarification.
2020 C3 Aircross Flair 130 BHP EAT6.
White with Black roof and orange mirrors & roof bars

routemaster1
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Post by routemaster1 » Sat Jul 23, 2022 4:46 pm

Juan Sheet wrote:
Wed Jul 13, 2022 5:47 pm
Simply put the design of the 1.5 is such that the cat and the DPF are vertical and at the front of the engine and are combined into one unit with separate components inside. Your previous 1.6 Blue HDI was a different engine design and therefore had the catalytic converter at the front, but the particle filter was a lot larger and at the rear.

So basically the older DPF was a lot bigger, so took longer to clog up and consequently took longer between regens than the 1.5 engine with a smaller DPF that needs to regenerate more frequently.

It's all about getting more out of a smaller space, making everything more compact and saving money of course.
I'm confused by this. My understanding is that the dpf is at the front and the catalytic converter is under the car. The dpf needs to be nearer the engine to enable it to get hot enough to burn off the soot.

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Juan Sheet
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Post by Juan Sheet » Sun Jul 24, 2022 12:22 pm

Not on this engine and here I'm using the 1.5 as an example:

C3AC CatDPF.PNG

The absorber (1) can store NOx particles at low engine temperature, and then release the NOx particles at high engine temperature.
The deNOx catalytic converter (2) converts the NOx particles in the exhaust gas into nitrogen (N2) and water by means of a urea solution injection.
The deNOx catalytic converter/particle filter assembly (3) traps carbon particles and removes NOx particles as the exhaust gases pass through.

So as you can see a compact design.

Here's a little more detail on the internals for you:

This is the DeNOx absorber

C3AC DPFA.PNG

"a" Exhaust gas inlet.
"b" Exhaust gas outlet.
"c" honeycomb ceramic block.
"d" Precious metals.

The carbon monoxide (CO) and the unburnt hydrocarbons (HC) are converted into water and carbon dioxide (CO2) by a chemical reaction.
When the temperature falls below 200°C, the deNOx absorber stores the NOx particles. Once this temperature is exceeded, the NOx particles are released to be processed by the deNOx catalytic converter.


This is the DeNOx catalyser

C3AC DPFB.PNG

"a" Exhaust gas inlet.
"b" Exhaust gas outlet.
"e" NOx inlet channels.
"f" Outlet channels for the NOx converted to water and nitrogen (N2).

To convert the NOx to harmless water and nitrogen (N2), a urea solution is injected upstream of the deNOx catalytic converter . On contact with the heat of the exhaust gas, the urea solution is converted to ammonia (NH3) which reacts with the nitrogen oxides and the oxygen contained in excess in the exhaust gas of diesel engines.


This is the DeNOx catalytic converter/particle filter assembly

C3AC DPFC.PNG


"a" Exhaust gas inlet.
"b" Exhaust gas outlet.
"g" Inlet channels.
"h" Outlet channels.

The particle emission filter is made up of entry channels closed at their end, which forces the exhaust gas to go through the walls of the channels. These work as a filter and retain the particles.
Essentially consisting of carbon and hydrocarbons, these particles on the particle filter burn in the presence of oxygen at a temperature of 550°C (natural regeneration or with the assistance of post injection).
A fuel injector, installed upstream of the particle emission filter, makes it possible to reach the combustion temperature of the soot by injecting preheated fuel into the exhaust system.
The walls of the particle filter also have a deNOx catalytic converter coating to increase NOx particle removal when the exhaust gas flow and temperature are higher.
C3 Aircross Flair 1.5 Blue HDi
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