Diesel Driving Style - Minimizing Soot Output

[jtay2024]

Hi All,

I've quite often driven carefully to try and keep my fuel costs down in my diesel civic. Recently out of interest I started monitoring the DPF regeneration frequency. How many miles between each regeneration.

I am wondering what peoples thoughts are when it comes to drive style to keep soot production low. It'd be interesting to see how many miles I could get between regeneration's through different styles of driving.

I have thought of a few types to try.

1) Low revs, higher throttle % acceleration (I expect this would produce the most soot as it lags the engine with lower boost & high load).
2) Normal driving with little thought of the soot production. (I'd expect maybe around 500 miles between DPF regen like this).
3) Acceleration at maximum of about 50% throttle and keeping the revs 1700+ RPM by changing up later. (I believe this would produce the least amount of soot).

Does anyone have any other thoughts or theories I could test driving style wise?

I'm doing this just out of interest rather than anything else. I also imagine that keeping soot production to a minimum would help stop oil contamination with soot, and fewer DPF regeneration's reduces fuel in oil percentage.

 

[OneLonelyBurrito]

Hi All,

I've quite often driven carefully to try and keep my fuel costs down in my diesel civic. Recently out of interest I started monitoring the DPF regeneration frequency. How many miles between each regeneration.

I am wondering what peoples thoughts are when it comes to drive style to keep soot production low. It'd be interesting to see how many miles I could get between regeneration's through different styles of driving.

I have thought of a few types to try.

1) Low revs, higher throttle % acceleration (I expect this would produce the most soot as it lags the engine with lower boost & high load).
2) Normal driving with little thought of the soot production. (I'd expect maybe around 500 miles between DPF regen like this).
3) Acceleration at maximum of about 50% throttle and keeping the revs 1700+ RPM by changing up later. (I believe this would produce the least amount of soot).

Does anyone have any other thoughts or theories I could test driving style wise?

I'm doing this just out of interest rather than anything else. I also imagine that keeping soot production to a minimum would help stop oil contamination with soot, and fewer DPF regeneration's reduces fuel in oil percentage.

This graph will probably answer your exact question, while not for your exact engine, but should be pretty representative.

 

[KJSmith]

I had an '11 Ford 250w/ 6.7.
It had a DPF filter.

If I remember correctly, keeping the engine under load to produce higher exhaust temperature would decrease DEF usage.
But you would use more diesel of course.

I only had it a couple of years...58k miles or so.
It seemed that the longer I owned it, the further it would go before regen.

As an aside....it would get amazing fuel milage between regens....like 26mpg or so.
Regens would just kill it on a full tank average...something like 9mpg during a regen that could last 15 minutes at highway speed.

 

[jtay2024]

This graph will probably answer your exact question, while not for your exact engine, but should be pretty representative.

View attachment 241072

Well this is very intriguing. It almost works the opposite of how I expected it to at low RPMS. For example, at 1500rpm, and 100Nm torque request there is a lot of soot loading. However at the same RPM and 400Nm it's much less.

I wonder if that's due to the EGR being open at lower loads and then having to close at higher loads to increase power. I remember reading somewhere that EGR reduces NOX at the cost of increased soot.

Interesting map that is. Thanks!

 

[jtay2024]

I had an '11 Ford 250w/ 6.7.
It had a DPF filter.

If I remember correctly, keeping the engine under load to produce higher exhaust temperature would decrease DEF usage.
But you would use more diesel of course.

Interesting. Perhaps having a higher exhaust gas temp helps to keep soot down by burning it more thoroughly.

 

[OneLonelyBurrito]

Well this is very intriguing. It almost works the opposite of how I expected it to at low RPMS. For example, at 1500rpm, and 100Nm torque request there is a lot of soot loading. However at the same RPM and 400Nm it's much less.

I wonder if that's due to the EGR being open at lower loads and then having to close at higher loads to increase power. I remember reading somewhere that EGR reduces NOX at the cost of increased soot.

Interesting map that is. Thanks!

With the combustion of diesel there is always a NOx vs soot trade off. You can have low NOx or low soot, not both. This specific engine was calibrated to have higher soot but lower NOx in the emissions testing RPM and loads areas. Once you get out of those areas, soot goes down but NOx goes up.

With a calibration like that, you can more easily package an SCR that can efficiently remove the NOx since a DPF is always capturing the amount of soot coming out of the engine, but an SCR can only handle a certain amount of NOx coming out of the engine.

 

[OneLonelyBurrito]

If I remember correctly, keeping the engine under load to produce higher exhaust temperature would decrease DEF usage.

Higher exhaust temp will increase DEF usage not decrease. Higher exhaust temps will typically decrease the amount of soot coming out of the engine while also increasing the oxidation of soot in the DPF so it regens less.

Interesting. Perhaps having a higher exhaust gas temp helps to keep soot down by burning it more thoroughly.

That's exactly what is happening, it just increases the amount of NOx, as shown in the graph below. When the temperature of the flame front gets high enough, not a lot of soot is produced as most of it is oxidized.

 

[b_b]

using a diesel additive will help that. archoil is a good one. im sure there are others.

 

[Dr_Dr3i]

OP, i think perhaps more important for soot production is the quality of your diesel fuel. I don't think it's worth worrying about exactly what rpm you need to be changing gears at all the time; just use the power you need when you need it and don't overthink it.

As long as you're using quality fuels (and an additive can help achieve that) and your compression is good, soot production should be minimal and mostly held in suspension by the engine oil. If it gets past the rings and into the exhaust is when you're loading the DPF with ash, which might be a different thing and which requires a high-temp additional burn to clear that ash out. The DEF system is further aftertreatment and not part of the DPF regen/cleaning cycle.

 

[eljefino]

And don't jump on the go pedal... ease into and out of it. You want the output power to catch up to the fuel input. Sudden transients can fart soot.

 

[KJSmith]

Interesting. Perhaps having a higher exhaust gas temp helps to keep soot down by burning it more thoroughly.

That is my understanding....higher exhaust temperatures will burn the soot out of the DPF on its own.

On Edit:
Looking around really quick on the web, it says that may have changed on the newer diesels.... apparently it has something to do with the way the EGR works now.

I can only give you my real-world observations on my '11 6.7.

I had a '02 7.3 that was stolen in '11.
IMHO, once the EPA got involved with diesels things went downhill.
I sold my '11 because I had no real reason to own a diesel, and they became to complicated and expensive to be a daily driver.

 

[tnt_motorsports]

Exhaust temperatures are your friend here. Higher is better to burn off soot. I have an Edge 2 on my Ram to monitor several different characteristics like fuel pressure, turbo boost, exhaust temperature etc. I use my truck to tow a camper so different application but higher temperatures usually equals better performance to a limit of course.

Just my $0.02

 

[fdcg27]

And don't jump on the go pedal... ease into and out of it. You want the output power to catch up to the fuel input. Sudden transients can fart soot.

Exactly!
You and I have both had NA Benz diesels and I'm sure that we both learned that you could blow a large black cloud at any fool tailgating your 240D.

 

[Jetronic]

Interesting. Perhaps having a higher exhaust gas temp helps to keep soot down by burning it more thoroughly.

DEF is used to counter NOx, not soot though. running at a higher load does reduce the NOx output.

 

[KrisZ]

If you remember old diesels without DPF and you followed one on the road, they produce the most soot when accelerating hard or under big loads.

Your modern diesel is no different in this regard. So keep acceleration minimal, rpm low and throttle to a minimum. This will produce the least amount of soot.

Now, if you want to accelerate hard, downshift to bring the RPM up instead of taking advantage of the torque curve and doing it from low RPM, which diesels are famous for.