VW to add particulate filters to its petrol engines
Discussion
I don't believe this has been brought up yet on here. Correct me if i'm wrong but see below:
http://www.autoexpress.co.uk/volkswagen/tiguan/965...
I think my leasing streak will finally be coming to an end.
Thoughts?
http://www.autoexpress.co.uk/volkswagen/tiguan/965...
I think my leasing streak will finally be coming to an end.
Thoughts?
Not the same issue as with DPF's.
GPF's regen on a closed throttle rather than needing a "special" run or anything so every time you back off they'll regen.
Honestly I don't see them being any more of an issue than cats are. ie while they can have issues probably 99% last the lifetime of the car.
GPF's regen on a closed throttle rather than needing a "special" run or anything so every time you back off they'll regen.
Honestly I don't see them being any more of an issue than cats are. ie while they can have issues probably 99% last the lifetime of the car.
The trouble is that with GDI (Gasoline Direct Injection) you get some nasty tiny particles which are rather harmful (like the diesel ones) and hence the latest Euro rules mean there is a limit on them which car makers have to stick by (in VW's case only for the duration of the test 
).
).Due to the much higher exhaust out temperatures of petrol engines (550-750°C) compared with those of modern diesel engines (250-450°C).
Petrol exhaust gasses also contain VERY LITTLE OXYGEN when running stoichiometrically (the amount of oxygen present is the exact amount needed for complete combustion of fuel) and under load.
Diesels burn leaner and have more available oxygen in the exhaust mixture.
For particulates to burn off during a DPF/GPF regen, a surplus of oxygen in the exhaust mixture is needed (so the catalysed oxidation/combustion of the particulates can occur) along with a high temperature in the particulate filter itself (to overcome the activation energy for this combustion reaction).
This means that for a DPF regen, high load is needed to give the required exhaust temperatures for oxidation of the particulate to occur.
Whereas for petrol engines, the exhaust is almost always hot enough for regeneration to occur thus all that is required for regen is a high enough oxygen content in the exhaust mixture for oxidation of the particulate which happens during overrun or low load scenarios. Therefore, GDF's do not require an active regeneration cycle like DPF's as simple everyday driving will do!
Also, particulates from petrol engines are much faster to oxidise than their diesel particulate counterparts. this means that there is much less 'soot loading' in a GPF when compared to a DPF, this means that GPF's are much smaller (GPF volume ? Engine displacement) than DPF's (DPF volume ? Engine displacement).
Hopefully most of this is correct, some of you probably know a fair bit better than me as this is just research I have done in the past out of my own interest.
Petrol exhaust gasses also contain VERY LITTLE OXYGEN when running stoichiometrically (the amount of oxygen present is the exact amount needed for complete combustion of fuel) and under load.
Diesels burn leaner and have more available oxygen in the exhaust mixture.
For particulates to burn off during a DPF/GPF regen, a surplus of oxygen in the exhaust mixture is needed (so the catalysed oxidation/combustion of the particulates can occur) along with a high temperature in the particulate filter itself (to overcome the activation energy for this combustion reaction).
This means that for a DPF regen, high load is needed to give the required exhaust temperatures for oxidation of the particulate to occur.
Whereas for petrol engines, the exhaust is almost always hot enough for regeneration to occur thus all that is required for regen is a high enough oxygen content in the exhaust mixture for oxidation of the particulate which happens during overrun or low load scenarios. Therefore, GDF's do not require an active regeneration cycle like DPF's as simple everyday driving will do!
Also, particulates from petrol engines are much faster to oxidise than their diesel particulate counterparts. this means that there is much less 'soot loading' in a GPF when compared to a DPF, this means that GPF's are much smaller (GPF volume ? Engine displacement) than DPF's (DPF volume ? Engine displacement).
Hopefully most of this is correct, some of you probably know a fair bit better than me as this is just research I have done in the past out of my own interest.
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