Theoretically, is there any way to get a passive regen in normal driving? In otherwords, why burn so much more fuel to boost the exhaust temps for a "cycle"? What is the temperature difference between normal running and a regen cycle? Is there any way to get close with the engine "working" that will require little help to get up to regen temps? City driving obviously wouldn't work for this, but running at elevated speeds/rpm's (highway driving, cruise on the country routes) should allow an opportunity to get up to temp better. I know regens work best at elevated speeds for extended times, but instead of a "cycle" why can't highway driving in and of itself burn out the filter?

Tractors do this - and the practice of "shift up, throttle back" boosts efficiency for lower-demand operations (lower RPM's, same ground speed, harder to push the same speed = working the engine harder than a higher rpm). In a nutshell it boosts fuel economy (hp-hr/gal) by better utilizing the power of the engine over a wider range. Because the engine spins slower the torque has to go up to do the same amount of work, which means the engine load is increased. By keeping the load on the engine up the system is able to initiate a regen in a passive state - theres very little, if any, extra fuel burned for the sole purpose of boosting EGT's.

If a truck engine is already working in propelling the truck/load down the road, shouldn't that be enough work to require minimal help in cleaning the filter through a regen process? Instead it appears quite the opposite - the higher the engine load the more active regen cycles (towing a trailer = less miles between regens than empty, the harder the trailer to pull the less miles between regens). I guess I don't fully understand the background on why a regen happens in a diesel (mainly the 6.4). I know why it does - to clean the filter of the soot it trapped - but that isn't a complete explaination. There are other systems that don't necessarily require active regens. Why the difference?

What is the threshold of regen temperatures? Are those temperatures ever reached in a non-active regen state? Can a curve be fitted to those parameters? (boost pressure/RPM? I would assume those would be a function of the engine loading).

 

It is my understanding that towing a heavy load results in less regens, not more. Also normal driving just does not cause the exhaust to get hot enough to burn the soot out.

 

In a NOx based or passive regen, soot oxidizes at 300C. O2 based or active regens reach temps of nearly 600C to oxidize soot. The 6.4L will regen passively under the right conditions, but less frequently than the 6.7L because it has less NOx in the exhaust after the engine.

A 6.4L should regen passively more often if loaded at 50% load than it will at 100% load simply because the engine is producing more soot than it can get rid of at 100%. The 6.7L has less EGR which means more NOx at engine outlet. Less EGR means less soot produced. Less EGR also means more NOx or lower regen temps.

Operators of 6.4L engines can benefit somewhat by using bio diesel fuel. Bio diesel produces less soot that also oxidizes at a lower temp than fossil fuel based soot. Due to the lack of energy in bio diesel, fuel economy will/may suffer.

 

There is more cause for concern with bio then less mpg's. I also has more potential for water so avoid it period...unless you are the one controlling the manufacture of it.

I agree with the thought process on the passive and active regens. If I am cruising empty I can go 400 + miles sometimes without a regen...passive ones are happening.

Loaded to 100% then my regens are around 130 miles apart. Simply too much soot to be handled by a passive regen.

 

We use Bio-diesel at thejob and it has a tendency for the fat in it to clot together and glop up the fuel filters in colder weather. They look as though u covered them in cake iceing. We also have the h20 issues Senix mentioned. The 6.0 engines hate the bio and it appears as though the 6.4 is starting to feel that same. The cummins and the Cats do not seem to particularly care for it either.