Then once a month for a couple of miles keep the car in fourth gear and hold the revs at 3k doing 70mph to let the engine and exhaust get proper hot.

During cruising, the exhaust will get hotter at 2500RPM than 3000RPM. Revving just makes noise and wastes fuel.

Plus its pointless in a 3 year old Rio, it does not have a DPF to clean. If you had a DPF and it need to regen you do not need higher than normal revs, the ECU controls the temps.

Unfortunately, emissions and fuel economy are not necessarily synonymous. In fact they are often diametrically opposed.

A few comments

Videodoctor, neither of our DPF cars have a dedicated warning light to tell you a regen is needed. On both the engine fault light will flash if you need to drive the car in a certain manner to force a regen, on both cars its the same, 30 minutes with the engine at 2500 rpm, thats about 70 in 4th on the motorway at a guess. If the warning is still flashing after this or turns solid you must take it to a dealer for a forced regen or the DPF will become blocked and unservicable requiring a replacement, very expensive. You manual should detail the facts for your specific car, never had a Ford with a DPF thus don't know for certain.

MikeTorque, even though I say it myself your comments are exactly the same as mine regarding the more fuel you use the more soot you produce, nice to see some common sense.

Unthrottled, you do not own a diesel car (by your own admission you do not like them and own a Focus 1.6 petrol) thus have no current experience of how a DPF works in the real world, I accept that you may have had diesels in the past but older ones with earlier emission controls either had no DPF or needed to capture less soot. My comments are based on my personal experience with DPF equipped cars over 40,000 + miles not what I have read or heard thus are IMHO more valid than your hearsay and textbooks. Your comment “If DPF is fitted, hard driving will raise exhaust gas temperatures and help with regenerations” is simply not a fact on the DPF cars we own, they either regen when the sensors tell them or every 300 miles, driving them hard to force a regen is an urban myth unless as I say above the warning light is flashing. How do you know that at 60 mph I waste more fuel doing a regen than at 70 mph, have you carried out tests. I don't know for certain but logic says that if I travel 17.5 miles in 15 minutes at 70 mph I use more fuel that I would travelling 15 miles in 15 minutes at 60 mph. On a flat road at 60 mph the fuel confuser says you are doing better mpg that on the same pice of road at 70 mph thus its logical you waste less fuel. But what do I know, I only drive 2 diesels with DPF's and you drive a petrol.

Knowledge of technical issues and choice of personal transport aren't directly related at all - false logic can be very dangerous.

OK, lets replace the words "its logical" in my original post with the words "it appears", happy now?

The first "logic" stays, all cars use less fuel at 60 mph than 70 mph, no arguement there surely.

Your empirical observations, while diligent, are crude (hot exhaust tip, wooly response,different engine note etc They do not give any insight as the nature of post injection.

Crude maybe but fact all the same and the same for both cars virtually. All that matters to me is I can tell when is regen is happening and experience tells me how long it takes meaning I can ensure it completes. Over a long period that "crude" knowledge should help me ensure the DPF's remain healthy and ensure that I waste as little diesel as possible doing that.

Error 403-Wouldn't let me edit the post, so here is the rest of it.

If 600C exhaust temperature is required for soot burn off, and your driving style produces an average exhaust gas temperature (EGT) of 250C, then the ECU must artificially raise the EGT by 350C. But if your driving style produces an EGT of 350C, then the ECU must only raise the EGT by a further 250C.

Therefore less fuel is wasted. ?

On a flat road at 60 mph the fuel confuser says you are doing better mpg that on the same pice of road at 70 mph thus its logical you waste less fuel.?

You are correct-whilst the DPF is not regenerating.

60mph should yield an easy 60mpg on the flat.

70mph " " " " 50mpg " " "

But if the confuser says you're getting only 35mpg during a regen, then clearly a large proportion of the fuel is simply being chucked into the exhaust. You would be as well driving faster with no penalty in fuel consumption whilst this is happening.

My choice of transport is based upon my financial situation (which was terrible) and a realistic view of the duty cycle. My average journey is too short to warrant a diesel.

If you had a diesel you could try it.

The diesel engines that I deal with are off-road and not equipped with DPF. But, I'll get some data from the guys that deal with on road diesels.

I am not trying to blind other posters with science, I am merely reporting what I know to be fact.

Nobody is trying to blind anyone with science-but a diesel engine is based upon some fairly well understood thermodynamics-and the empirical evidence matches the theory very well.

No sane person would claim that one indirect measurement, whilst not without merit, constitutes a general 'fact'.

Concrete

My personal experience is providing you do decent runs occationally and don't drive solely in town you should have no problems with DPF's. It is critical you use the correct low ash oil, if you don't rather than soot blocking your DPF ash residue will and that does not burn off, in fact regens produce ash when the soot is burned off but only in small amounts if the oil is the correct one, says this in both our handbooks. I don't have any mechanical engineering qualifications and neither does the wife but we can both tell what is happening and Skidpans experiences are very similar. There are tens of thousands of diesel owners out there who don't know what a DPF is and thus have no idea if they have one, they carry on driving their cars and never have a problem. Most that have problems have them because thay bought a car with the wrong engine for their type of usage.

Having said that it does seem unlikely that we will have 2 diesels in the house in the future, having driven a Skoda some time ago with the 1.4 TSI 122 bhp petrol I quite fancy that engine in a smaller car, maybe a Yeti or Seat Leon. Any petrol will have to be a turbo, have become used to the low down power of diesels and have come to hate the revvy nature of modern 16 Valve petrols. The 1.4 TSI appeared to give the best of both worlds.

Concrete-you don't need to know any of this! This is supposed to a be a fun discussion about how to get the best bang for your buck.

My mum has a diesel fitted with DPF and has no problems with it at all. She doesn't have any scientific/mechanical knowledge at all.

Edited by dieselnut on 22/01/2012 at 21:27

Dieselnut

There is no need to worry about regen temperatures, they are controlled by the ECU as part of the process.

Double post again, so much for Google Chrome being better than Internet Explorer.

Edited by skidpan on 23/01/2012 at 07:31

Although regenerations are often started by mileage counters in the ECU (i.e. at fixed intervals), I don't believe the duration of the regen is fixed for every car. The duration is determined largely by the pressure sensors measuring the pressure drop across the DPF matrix. Once this hits the ECU's lower threshold for soot-loading, the ECU will stop the process and return to normal running.

So if the mileage counter orders an 'active' regen after you've just done a couple of hours at a steady 75mph / 2,000rpm on the motorway, the DPF should only have a light loading of soot because it will have been passively regenerating during the motorway run.

This was the case in my Mondeo, and seems to be the same in the Volvo. Of course, every manufacturer's DPF set-up and ECU coding is a little different.

On the Briskoda forums, a poster ran an experiment with a Superb 2.0, logging the DPF soot-loading data from the ECU during a motorway run. I can't recall the data exactly, but at the start of the motorway run, the soot loading was around 50%. After 10 minutes of running at a steady 2,000 rpm in top gear, the soot loading had fallen to 10%. OK, it's just one particular make and model of car, but it shows how quickly 'passive' regeneration takes place under suitable driving conditions.

At the risk of opening a MASSIVE can of worms, I also believe that fuel choice influences the duration of regenerations. I'm experimenting with Shell V-Power currently, on my 6th consecutive tank, which has shown an average 3% improvement in economy.

As I said above our Ceed does a regen every 300 miles, we have used Esso, Total, Tesco, Asda, Morrison, Sainsbury's locally, probably others on holiday, its exactly the same on all of them. The car started a regen for the wife today at exactly the predicted mileage just as it always does. With branded fuels being about 5p per litre more than supermarket stuff I would have to be seeing nearer a 4% saving in fuel before it made it worthwhile but the wifes and my experiences do not indicate any difference at all. The handbook says use diesel to BS EN 590 and (correct me if I am wrong) all pump diesel in the UK has to comply with that standard, seen to remember all the pumps I have used say it does.

Edited by thunderbird on 23/01/2012 at 17:57

RT-I wouldn't consider EN590 to be a 'bare minimum'. The composition of fuel is a compromise of diametrically opposed attributes. Improving one aspect tends to make something else worse. There's surprisingly little 'tinkering space' within the specs-which is why I'm always fairly skeptical of big gains. But the shorter regenswould be a definite plus for those with Euro V diesels.

In an earlier post , you said that the duration of regens had fallen from 15-20 minutes down to 10 minutes. With an average of, say, 1.5 regens per tank, I reckon that would give you your 3%.

Dunno why it would be though. I wonder if they add some sort of ceria compound (the active ingredient in Eolys) to the fuel to help with soot burn off. But if it's that good, the authorities would simply include it in the specification for EN590 diesel.

It would be helpful if Shell were less coy-most people want to patent and publish!

As mentioned in the other thread, until recently Shell made lots of the fact that V-Power has a % of GTL synthetic compenent which boosts the cetane number and is supposedly very clean-burning (therefore, a bit less soot), but as you say they've removed all that detail from their website in recent months.

Perhaps the higher cetane number of premium diesel helps with reducing soot by enabling (fractionally) more complete combustion?

When Fifth Gear did back-to-back dyno testing (using a chassis dyno to minimise grip-induced errors), both V-Power and BP Ultimate gave an immediate 6bhp increase (161bhp vs 155bhp) over supermarket EN590, with just a drain and flush of the tank and lines, with no ECU adaptation time etc.

Genuine question, why does a higher cetane fuel tend to increase soot? If it ignites faster, I would've thought that mean a more complete burn ...

I wonder if the multiple injections per cycle (pilot & up to 3 main injections) in modern CR diesels muddy the waters, by reducing incomplete combustion?

With regards to the 5th gear test of premium diesels I am not doubting that they found another 5 or 6 bhp by simply using the expensive higher performance diesel but surely that is only part of the story. If the extra bhp was above 4000 rpm how often would that extra power be accessed by the average driver. What I would want from an expensive fuel would be something I could feel the benefit of when I drive the car rather than something that can only be measured on a dyno or rolling road. Better pick up when you press the throttle would be one benefit every one could feel, improved mid range torque would be perhaps less noticable but it would undoubtably help by meaning less gearchanges to get the same performance. If shorter regens were another benefit that is something that would attract me and would probably be quantifiable. But unless there was a noticable improvement in economy to offset the extra 10 to 15 p per litre that our local BP charge I don't think I will bother, I can do quite a bit with the £150 a year it would cost me for one car alone and even though some say they have seen an improvement many say they have seen none.

Only way to tell for definite would be to do a comparrison, may try once the temps rise and summer diesel is back in the tanks at the garages. Having done a similar experiment a few years ago with a petrol car I don't expect to see any improvement and that was a car that the manufacturer said ran best on 98 octane but it was OK to use 95, actually as low as 91 was acceptable.

If we exclude "boy" racers who drive flat out everywhere, what % of time do we actually drive at full throttle? Around 1% is my guess.

For all the time we're driving at part-throttle, there's always more power/torque available simply by depressing the accelerator a little more - so whether it's "high performance fuel" or "high performance tuning gadgets" they're just lining someone else's pockets in my book.

Exactly, isn't that what we do to overtake/accelerate.

If we exclude "boy" racers who drive flat out everywhere, what % of time do we actually drive at full throttle? Around 1% is my guess.

For all the time we're driving at part-throttle, there's always more power/torque available simply by depressing the accelerator a little more - so whether it's "high performance fuel" or "high performance tuning gadgets" they're just lining someone else's pockets in my book.

Exactly, isn't that what we do to overtake/accelerate.

But even overtaking/accelerating, we rarely use full throttle - so more than we use is unnecessary.

The part I was referring too was the "depressing the aceelerator a little more" line. Agree we rarely use 100% throttle very often, think even 1% would be pushing it.

I have to congratulate the OP as i never thought such a boring topic would end up with so many replies.