Houston - We have a regen !
(Or maybe ' The regen has landed....' )
I did one of my Sunday runs today and thought I would bring the laptop along even though the clogging % was still only getting up towards 80% and a regen wasn't yet due, or so I thought.
I just wondered what temperature the dpf will rise to under a hard acceleration along a motorway sliproad from standstill. I had just turned on the dpf pressure monitoring too when I pulled off into the services half a mile down the road (had been driving for 10 miles on the motorway at this point)
I went straight through to the exit of the services and waited for the sliproad to be clear and then set off, accelerating hard. The dpf temperature was rising nicely and I was surprised to see it rise to 450 celsius, and then 500 celsius......
Suspecting a regen was starting I lifted off the throttle and the turbo gauge dropped like a stone, to confirm it. The clogging % value at the start of regen was only 80% !
I've captured a full regen cycle and have put the graphs here...
The bottom line is regen %. The line above is the clogging %. The middle line is dpf pressure which seems to fall steadily during the regen (as expected)
Pre-regeneration running, hard acceleration indicated by high dpf pressure.
PreREGEN | Flickr - Photo Sharing!
Regen starts, the top two lines show pre-cat and dpf temperatures continuing to soar after intial hard acelration initiate REGEN | Flickr - Photo Sharing!
Regen ended. The clogging % is reset to 10.45% endREGEN | Flickr - Photo Sharing!
After this regen cycle the rate of rise of clogging % is the same as it was before the regen. It is still rising at about 5.2%/hour
I reset my dpf to 0% clogging last week when I performed a 'replace dpf' routine, which tells the ECU to assume that the soot loading of the dpf is zero (IE it's a new one)
The regen started at 80% clogging. Why ?
I suspect that the signal from the pressure sensor reported that there was too much soot in the filter.
Is it relevant that this happened immediately after hard acceleration ?
Possibly. As seen in Fireman's data, his pressure readings at higher revs are lower than mine. I wonder if the pressure signal is evaluated only under higher loads and higher revs, at the time when you really do need free flowing filters.
Just pootling about in traffic isn't going to produce those sustained high load, high rev conditions very often and you are hardly likely to notice the effect of a fully soot loaded dpf with gentle driving.
Why didn't the clogging % value reset to 0% ?
I suspect that when regeneration ended the final pressure readings were evaluated and the countdown timer preloaded wiht a value representative of when the next dpf regen is estimated to be needed.
What should I do now ? (!)
I think I would like to capture another regen before doing any more drilling, just to check that the clogging % rises to much nearer 100% next time.
Some of the 'status' information I just read from my ECU
Particulate filter lamp: Off
Particulate filter state: Not clogged
Forced regeneration state: Not active
Last DPF replacement odometer, km: 570.00
Odometer from last regeneration, km: 19.80
Average temperature of last 5 regenerations, °C: 635.76
Average distance from last 5 regenerations, km: 551.00
Average duration of last 5 regenerations, sec: 719.00
Average duration of last 5 regens = 12 minutes. I think todays regen was also about the same when considering the distance I travelled with the the cruise control on at 70mph in fifth gear.
I think it is clear now, that clogging % is not a reliable indicator of the soot loading of the dpf. Clogging % seems to behave as if it is just a count-up accumulator which until we have more data from other users, seems to just always count up at a rate of roughly 5% per hour, regardless of the soot loading. I did notice some slight increase in rate of rise under very hard accelration, but not enough to be measured reliably and it could have just been the refresh rate of AlfaOBD which made it appear that the rate had changed.
I suspect that 'differential sensor pressure' (another AlfaOBD typo - it should read 'differential pressure sensor') is a much more reliable indicator of soot loading, partially confirmed by my observations of the pressure released from the temperature sensor mounting hole, as well as the static differential pressure sensor readings at various rpm while stationary.
All in all, the implications for drilling into the dpf via the exit pipe look very good. All you need to do is somehow establish that you have a blocked dpf problem, either by fitting a 1 bar (or thereabouts) pressure gauge onto the dpf itself ( I think it's a standard 14 or 15mm threaded coupling), or by observation - if it sounds like a burst airline when you take the temp sensor out and run the engine at 2000rpm, or by using AlfaOBD or FES to check the output from the differential pressure sensor itself at various revs and comparing to what I assume to be a good dpf - Fireman's data.
Some more pressure readings at different revs will be valuable here to get a better feel for other dpfs in general (and we need to consider some measurement tolerance too)
Judging by the fact that this regen happened for me before 100% clogging was reached, it looks like i will need to liberate a bit more dpf core material with some more drilling if I want to get the figures down to what a healthy dpf, like Fireman's dpf, operates at.