Learn me diesel smoke

I was on my way to work this morning, huffing the soot of a diesel Silverado in front of me (on flat ground, no less!) when I started thinking.

Why is it that a 700 hp diesel prototype race car with no mufflers, particulate filters, or urea systems can drive at full throttle and not produce a significant amount of soot, but a late model Duramax with less than half the power will constantly belch soot out of it driving normally? Is it just the mentality of "add more fuel, she'll go faster" that keeps tuners from keeping the combustion process clean?

Unlike gas motors, diesel motors make their power with more fuel, not more air.

It's a matter of difference in starting design when considering powerstroke/cummins vs. daytona/audi lemans cars.

Most newer diesels have particulate filters.

Newer engine designs using very high pressure injectors atomize the fuel better so it burns more completely (black smoke is basically unburnt fuel).

Overall better controls so only the exact amount of fuel required is injected for a given situation.

The fuel for each power stroke is injected in very fast, rapid bursts rather than all at once. Again, to induce a more complete burn.

A lot of diesel guys love to put down Banks systems as expensive for the power increases. However, they seem to put in the extra design work required to get extra power with minimal-to-no smoke increase. Personally, I respect them for that.

In the case of the TDI LeMans cars, they also use a special Shell fuel that is apparently forumulated to produce less smoke. VAG knew that if the car won the race belching plumes of black smoke, it wouldn't matter how fast or efficient it was so steps were taken to make sure that didn't happen.

I thought the Lemans car did have particulate filters.

Tune it rich...... when they start pushing 50 pounds of boost into an engine with 18:1 compression, they tend to err on the side of too rich. But in bone stock trim, I wonder if it's not oem's keeping mileage down, and expensive TD motors safe

Not always. Running it rich can also spike EGT's. The guys pushing envelope on HP keep a keen eye on their EGT gauges since it's a fine line between glowing and meltdown.

Yeah - its a tuner thing. My duramax does not smoke at all even floored with a load on it. The only time it ever tosses up a cloud is when you get on it, then lift just before the turbo spools, and quickly hammer it again.

By any chance, did that truck have "truck nutz?" If so, 'nuff said. Some of the diesel crowd love their plumes of black smoke and drive it in a manner to smoke everyone out. If it was a stockish looking truck, it could have been cold since they will smoke more cold than hot. I had a 7.3 powerstroke and that thing never smoked. Even towing a trailer, I couldn't see smoke behind me.

It is true that diesel EGTs do increase as the mixture increases, the opposite of gas engines.

Another reason that the truck could smoke and the race car not is that the race car probably has clean fuel injectors. Can you say that about the truck?

The diesel LeMans cars do use a particulate filter, which is a big part of why they are so squeaky clean and quiet buzzing around the track. Diesel particulate filters are awesome!

http://en.wikipedia.org/wiki/Audi_R10_TDI

Bryce

'92 Cummins TD, old 12V unit, approaching 260k miles...and yeah, it smokes on start up, and when you romp on it. But during normal driving, not into the boost, I never see smoke. Smoke's nothing to be proud of, and frankly hurts the perception of diesels that those of us who like them are trying to dispell. Heck, I have a '78 Mercedes 300D that only barely smokes on startup, when cold. I haven't washed it in over a year and there's none of that characteristic black soot on the back bumper.

Ah, didn't know that the R10 had particulate traps! Either way, this was a late model Chevy HD truck that looked rather stock and I didn't see a tuner on the dash for it either.

All of this got me thinking about how there are no emissions laws for diesel vehicles in Georgia when they are generally the most polluting* vehicles out there.

*smoke, soot, and other general nastiness.

volvoclearinghouse wrote: '92 Cummins TD, old 12V unit, approaching 260k miles...and yeah, it smokes on start up, and when you romp on it. But during normal driving, not into the boost, I never see smoke. Smoke's nothing to be proud of, and frankly hurts the perception of diesels that those of us who like them are trying to dispell. Heck, I have a '78 Mercedes 300D that only barely smokes on startup, when cold. I haven't washed it in over a year and there's none of that characteristic black soot on the back bumper.

My brother owns an old Mighty Max with a turbo-diesel swap out of an older Ranger and it doesn't EVER smoke as far as I can tell.

If I recall, Diesel "smoke" is mostly solid carbon and actually less toxic (or "bad") than gasoline smoke/exhaust. You don't want it coming out your exhaust because that's energy you're wasting that could have been turning the wheels.

Did this smoker have one of these?

http://www.stupidiotic.com/product_info.php?cPath=9_15&products_id=169

sobe_death wrote: All of this got me thinking about how there are no emissions laws for diesel vehicles in Georgia when they are generally the most polluting* vehicles out there.

All vehicles sold, diesels included, must meet federal (EPA) requirements. While GA might not perform emissions tests on older vehicles, those vehicles would still have met EPA requirements when new. Running tuners and such is plenty common in states with emissions tests because they allow the truck to go back to stock in seconds.

Bryce

sobe_death wrote: Is it just the mentality of "add more fuel, she'll go faster" that keeps tuners from keeping the combustion process clean?

Yes.

Gale Banks doesn't do stuff like that... his engines hold world records and they don't smoke.

As he puts it... smoke is energy that you paid for that you're throwing away.

93celicaGT2 wrote: Unlike gas motors, diesel motors make their power with more fuel, not more air.

Not quite.

As with any vehicle (gasoline too), you need to burn more fuel to make more power, but to properly burn that fuel, it needs to be well-atomized in a good amount of air.

Diesels always operate lean of peak EGT. Adding fuel raises EGT. On the flip side, you can just add more air (boooooost) to get EGTs back down, so you that can add more fuel. There are limits of course, mechanical and otherwise (the "smoke limit" for instance, which is the max RPM where combustion can still occur entirely in-cylinder)

I do remember reading that the last 5 to 10 percent of power capability for a given airflow/timing will result in some smoking, but this doesn't mean that smoke = power. Rabbit Diesels are kinda proof of that...

not to say that diesel you were following was also not abused and failing. While pretty bullet proof, you CAN kill them if you try hard enough