All diesels - Which driving style produces the least diesel soot

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Wed 18 Jan 2012 12:49
All diesels - Which driving style produces the least diesel soot - Chris23

Soot is a clear enemy of the modern diesel as it blocks EGR devices and DPF but how do you avoid making the soot in the first place?

I have heard four theories:

1.Soot is mainly generated when a car is being driven hard which is why drivers accelerating hard from roundabouts get the characteristic black smoke but not at steady speed.

2. A hard driven diesel burns the soot that both hard & soft driving generate but which only hard driving will burn up leaving it to cause damage in a gently driven car.

3. It is about turbo boost. An small engine with lots of boost produces more soot than a bigger less boosted engine producing the same power.

4. It is about the fuel that you buy.

Does anybody know?

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Wed 18 Jan 2012 13:04
All diesels - Which driving style produces the least diesel soot - skidpan

You should not see any black smoke out of a diesel fitted with a DPF but if you constantly drive hard you will fill it up quicker, simples.

Driving an old diesel hard may well have shifted any soot build up but to clear any build up in the DPF a regeneration is required, it simply cannot be blown out even though some maintain it can, its an urban myth. Regens take place when required and are controlled by the ECU, you cannot force one yourself.

Don't think it makes any difference, the way you drive will be the biggest factor.

Some say the expensive fuels are better but having driven turbo diesels since 1996 and never having used expensive fuel and very rarely use branded fuel, most supermarket stuff for me, I have never had a problem thus I think its all marketing. Supermarkets have a fast turnover thus their fuel is fresher, the expensive stuff may have been in the tanks for months gathering moisture and deteriorating.

My theory for the past 16 years has been to drive normally maintaining traffic speed and overtaking when necessary, seems to work, never had a problem with an EGR or DPF.

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Wed 18 Jan 2012 13:53
All diesels - Which driving style produces the least diesel soot - unthrottled

Driving a diesel engine hard will produce less soot per kWh of useful work. Period. Forget about the momentary puff of black smoke you sometimes see as the turbo spools up. It is the net effect that matters.

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Wed 18 Jan 2012 14:22
All diesels - Which driving style produces the least diesel soot - skidpan

Driving a diesel engine hard will produce less soot per kWh of useful work. Period. Forget about the momentary puff of black smoke you sometimes see as the turbo spools up. It is the net effect that matters.

Driving a diesel hard will also use more fuel. Use the torque which is what a diesel is about and let the DPF sort itself out as necessary, it works for most people like that.

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Wed 18 Jan 2012 14:58
All diesels - Which driving style produces the least diesel soot - unthrottled

You see by driving 'hard', I mean 'loading' (ie using the torque) the engine, whereas most people think of driving hard as revving the engine. Engines are always more efficient under load: Here's some data from a 10 litre 6 Cyl marine diesel in case anyone is interested. Automotive diesels will be similar

RPM load BSFC* (g/kWh)

1500 10% 328

" 25% 230

" 50% 202

" 75% 198

" 100% 198

2200 10% 464

" 25% 282

" 50% 232

" 75% 221

" 100% 220

Notice how the efficiency drops off markedly below 50% load especially at the higher speed. So to save fuel-quit feathering the throttle, get your foot down-then get into top gear!

*BSFC =Brake specfic Fuel consumption. 200g/kWh equates to about 42% overall efficiency.

Edited by unthrottled on 18/01/2012 at 15:02

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Wed 18 Jan 2012 16:29
All diesels - Which driving style produces the least diesel soot - Glaikit Wee Scunner {P}

Many amost new diesel cars seem to produce black smoke continously when climbing hills. I follow enough on my commute. Fords and Vauxhall seem to be the usual culprits(I know they are more common).

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Wed 18 Jan 2012 16:42
All diesels - Which driving style produces the least diesel soot - madf

Driving at night with following headlamps illuminating my exhaust, I have been able to produce a cloud of grey smoke by acclerating hard,,, in every diesel I have ever driven.

Rarely visible in daytime tho'.

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Wed 18 Jan 2012 16:46
All diesels - Which driving style produces the least diesel soot - diddy1234

Thats because they are practicing to join the Red Arrows display team :-)

Me included !

But seriously I have not had any sooting problems with the Diesel Rio in nearly 3 years of ownership.

However, I do like to open the car up to 3k rpm driving up a known steep hill on my way to work.

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.

I then drive like normal to work for the rest of the journey.

I never do any of this 'italian tune up' when the car is cold though.

Hardly ever noticed soot.

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Wed 18 Jan 2012 16:52
All diesels - Which driving style produces the least diesel soot - unthrottled

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.

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Wed 18 Jan 2012 16:56
All diesels - Which driving style produces the least diesel soot - skidpan

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.

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