Retrofitting old cars for cleaner exhaust

[oil pan 4]

As you said, one of the best ways to burn up smoke is install a turbo or turn up the boost slightly.
In my 6.5L diesels short life as a non-turbo it did smoke a little bit, then after I put the first turbo on that got rid of nearly all the smoke and improved fuel economy 2 to 2.5 mpg or by almost 10%.

To further reduce smoke production and engine oil consumption on my 6.5L I machined the heads so I could put actual seals on all the valve stems. The intake valves had something that barely resembled or functioned as a seal and the exhaust valves had nothing.
I didn't have to do it but I did.

[Piwoslaw]

Originally Posted by oil pan 4

If there is a DPF doing its thing near you it is producing colorless odorless diesel particulate in the 1 to 2 micron range it defeats all your body's senses and defenses. And you unknowingly breath the particulate deeply into your lungs.
The DPF does eliminate most of the diesel particulate but what it does produce is exceptionally bad for you.

With a non emissions controlled diesel the particulate is big, from 20 to 250 micron is what I am hearing. You see it you smell it and react to it you don't breath it in, unless you really like the smell of burned diesel.

So non-controlled diesels create only large particulates and controlled diesels only create small particulates?

Or...

Non-controlled diesels create all sizes of particulates, while controlled diesels filter out most of the large particulates?

If the latter, then do non-controlled diesels create less, more, or the same amount of the small particulates as controlled diesels?

Originally Posted by RustyLugNut

Diesel and gas engine controls will become more alike as time goes by.

Diesel and gas engines will become more alike as time goes by.

[oil pan 4]

The DPF system stops up to 85% of particulate matter.
What gets through is too small to be seen at that quantity and too small to be smelled.
All the particulate made by emissions controlled diesels is covertly trying to get inside you.

From what I have been able to find non emissions controlled diesels do make particles of all sizes. But most of the particles are big. They are big enough to be captured by a standard paper air filter installed on the exhaust such as found on underground diesel powered mining equipment. If most of the diesel particulate was DPF sized, a lot of them would go right through a standard paper air filter.
If you have to breath the exhaust, in an underground mining environment diesels are preferred, they create very little CO compared to gas and their exhaust soot is easy to trap.

If you cant see or smell the particulate how are you going to avoid it?
When you choke on diesel smoke that is your body's way of telling you "this is bad for you".
With the 1 to 2 micron particles I guess ignorance truly is bliss, until it catches up with you a few decades later.

[RustyLugNut]

Originally Posted by oil pan 4

The DPF system stops up to 85% of particulate matter.
What gets through is too small to be seen at that quantity and too small to be smelled.
All the particulate made by emissions controlled diesels is covertly trying to get inside you.

From what I have been able to find non emissions controlled diesels do make particles of all sizes. But most of the particles are big. They are big enough to be captured by a standard paper air filter installed on the exhaust such as found on underground diesel powered mining equipment. If most of the diesel particulate was DPF sized, a lot of them would go right through a standard paper air filter.
If you have to breath the exhaust, in an underground mining environment diesels are preferred, they create very little CO compared to gas and their exhaust soot is easy to trap.

If you cant see or smell the particulate how are you going to avoid it?
When you choke on diesel smoke that is your body's way of telling you "this is bad for you".
With the 1 to 2 micron particles I guess ignorance truly is bliss, until it catches up with you a few decades later.

But, remember we are talking about mass. A diesel with a DPF has 85% of the particulate mass removed from the exhaust. This leaves the sub micron particles to pass through. There have been studies that show that DPFs move some of the larger particulate mass into the sub micron range. However, the argument that it is better to have no DPF is utterly false as large particulates are cause for common lung, nose, throat and eye cancers. They cannot be ignored and removing them is the first step. Non DPF equipped diesels still produce a measure of sub micron particles. Studies on sub micron carbon emissions are still on going and inconclusive but I have no doubt the findings will see that long term exposure will result in various maladies and ailments.

There are various methodologies where we can trap and destroy these sub micron carbon particles, but it also behooves the manufacturers to work on the combustion technologies that will prevent these particulates from forming in the first place.

[Piwoslaw]

So all diesels produce sub-micron particulates, DPF-ed engines let out the same amount (or slightly more) as non-DPF-ed?

I read that the hotter your engine (or the hotter the exhaust) is running the less particulates it produces. Unsure whether the reduction is the same for all sizes, or whether only certain sizes are reduced. The price is more NOx.

[RustyLugNut]

Originally Posted by Piwoslaw

So all diesels produce sub-micron particulates, DPF-ed engines let out the same amount (or slightly more) as non-DPF-ed?

I read that the hotter your engine (or the hotter the exhaust) is running the less particulates it produces. Unsure whether the reduction is the same for all sizes, or whether only certain sizes are reduced. The price is more NOx.

All diesels produce sub-micron particulates (SMP). DPF use tend to result in more. Also, higher pressure injectors produce more SMPs by virtue of the much smaller droplet size they produce. To be exact, modern high pressure injection systems produce only about 20% by mass particulate mater that is larger than a micron. The rest is sub micron. Oxygenated fuel additives can also increase the amount of SMPs as larger droplets are broken up into smaller ones.

It is not so much that heat reduces particulates but more so that good combustion results in more heat and less fuel is turned into particulate mass. In other words, the particles are smaller and less massive though numerically the same. But, as you pointed out, this results in increased NOx.

When a fuel droplet enters a sufficiently hot combustion chamber it's surface starts evaporating and mixing with oxygen. Once the mix reaches the lower flammability limit, it starts burning. The middle of the droplet, not exposed to the oxygen depolymerizes and releases it's hydrogens resulting in a complex mix of carbon forms. This is referred to as nucleation. These particles can combine into larger particles. This is accumulation mode.

As Oil Pan4 pointed out, the deletion of EGR can reap huge performance gains. EGR and more specifically, cooled EGR causes the fuel droplet to enter a combustion chamber with reduced oxygen resulting in a lazy evaporation and combustion rate around the fuel droplet. The burnt exhaust gases also provide a buffering heat capacity sucking energy from the combustion reactions. This all reduces peak temperatures and the formation of NOx but has the adverse effect of increasing the mass of particles as the fuel droplet is not as well vaporized before it enters nucleation and solidifies. High pressure injection reduces the droplet size to begin with but it just means there are more particles produced, thus the bias to SMPs. If you could do away with the EGR, the greater availability of oxygen causes less massive (smaller ) particles and more power is available.

Note that a properly operating EGR system will reduce the flow of exhaust to the intake stream as engine load is increased as less oxygen becomes available to an increased mass of fuel. At lambda=0.8 what is generally regarded as the threshold for smoke to appear, the conditions are similar to those under EGR. The droplet finds less oxygen to combine with and burn and consequently, the particle mass increases. Thus the term "Rolling Coal" was coined as the smoke becomes very noticeable. It is not that there is an excess of fuel per se, but more correctly, the fuel is finding it difficult to pair up with an oxygen. Thus, it more readily nucleates and accumulates into the thick smoke we have all seen. The deletion of EGR really helps performance in the load ranges below lambda=0.8. This is where most driving is done and thus you can really feel the difference in added performance and fuel economy.

The above is a gross simplification of the process but it should give you a feel for what is happening in a diesel engine's combustion chamber.

[pgfpro]

RustyLugNut

Thanks for the above post. This makes it clearer for me now.

What are the Audi R10 TDI Le Mans Proto type LMP1 doing differently that the engine doesn't produce any smoke? I'm clueless when it comes to diesel technology.

[RustyLugNut]

Originally Posted by pgfpro

RustyLugNut

Thanks for the above post. This makes it clearer for me now.

What are the Audi R10 TDI Le Mans Proto type LMP1 doing differently that the engine doesn't produce any smoke? I'm clueless when it comes to diesel technology.

But, as we have emphasized in this discussion, providing enough oxygen is paramount. Elevated boost is certainly in the formula. A friend who is a BMW/Audi tech thinks the Le Mans racers use elevated injections pressures well above the 2000 bar of road cars. This gives them more injection timing control and provides exceedingly small droplets to burn. They don't have to worry about extended reliability in the range of years. And remember, even though we don't see "smoke" there are still the SMPs which as Oil Pan4 pointed out, you can not see or smell.