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I've read on the internet, in a couple of maintenance books and asked a few buddy mechanics and they all seem to point to the fact that a healthy diesel engine should not produce black smoke and that the common reason why this happens is because of too much fuel to not enough oxygen leading to incomplete combustion.

If the fuel is not completely burnt, then all that fuel is wasted which is not what I would expect in a racing context, so what gives? Why don't they cut on the amount of fuel injected into the engine so as to maintain a proper fuel/air ratio? Or better yet, increase the amount of air being rammed into the engine (at least as long as it wouldn't hurt the power to mass ratio)?

To add more confusion, I took a look at some footage of the Audi R18 TDI and I failed to notice any black smoke, which makes perfect sense, given the nature of the type of contest it is taking part in (efficiency anyone?).

So why are diesel dragsters wasting fuel and producing soot?

Zaid
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user1969903
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3 Answers3

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The Primary Reason for Excessive Soot in Diesel Dragsters is Incomplete Combustion

Something to keep in mind regarding diesel dragsters is that they do not use any emissions equipment to more effectively burn unburned fuel and oil contained in diesel fuel which is essentially kerosene.

Emissions devices NOT on a diesel dragster

  • Exhaust Gas Re-circulation devices or EGR's are absent

  • Oxidation catalyst devices are absent

  • DEF injection systems where ammonium or urea are injected into the system as an fluid are absent

Additionally, excessive valve overlap is tuned into the system to ensure the intake charge flushes the combustion chamber of exhaust gasses. These leads to excessive unburned fuel escaping from the exhaust valve and into the atmosphere, this unburned fuel is partially burned in the exhaust and is turned into DEP (diesel exhaust particles) which are primarily just carbon.

This is what you see with the thick black smoke from diesel dragsters, carbon.

DucatiKiller
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From a practical perspective: It is most likely that they still see a power increase by progressively injecting more and more fuel - even with the extraordinary soot production, which isn't a limiting factor in these conditions.

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Diesel fuel is heavy in oil residual as it is far less refined than is gasoline. However please understand though both burn in internal combustion engines diesel runs on different processed product. Gasoline is measured via Octain and this is a completely different line as Cetain, the processing method of diesel. Jet fuel, Kerosine and diesel share this proccess! Now as to Tractor pull rig's and the plume of heavy soot this took tons of compression, huge valves to flow it all and injectors with pencil size holes where an normal diesel has injector sprayer holes as small as a doctors smallest needles.

quickC 4 U
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