Comparing different approaches to emissions

   / Comparing different approaches to emissions #11  
Great write-up. The only correction is the regen temp for DPF is 600 deg C or about 1100 deg F which is why some systems use a diesel injector in the DPF to help get the temperature up to burn off the carbon buildup.

I will further research compact tractor DPF temps in the next few days. I am nearly certain DPF in my Kubota L3560 reaches soot incineration temperature solely through throttle advance to 2,200 engine rpm. In abstract it would seem logical there would be one threshold temperature at which soot would incinerate cleanly and completely within DPF. Perhaps, perhaps not.
 
   / Comparing different approaches to emissions #12  
Beginning about thirty-three horsepower most tractors have Diesel Particulate Filters (DPF).
If not DPF, the less used alternative emission technology is Diesel Oxidation Catalyst (DOC).
Both the DPF and the DOC are honeycomb ceramic filters.
The DOC forces engine exhaust over a honeycomb ceramic structure coated with platinum, palladium, and rhodium catalysts. These catalysts oxidize carbon monoxide and hydrocarbons into carbon dioxide and water at hot exhaust temperature.


A DPF is a ceramic matrix which accumulates particulates/soot at temperatures below soot ignition temperature. During regeneration, when DPF achieves and maintains at least 500 degrees Fahrenheit, the temperature of a hot kitchen oven, accumulated soot incinerates during a few minutes.

It occurs to me that enclosed volume of DPF may influence temperature required to accomplish thorough incineration, with greater volume DPF requiring higher temperatures to incinerate soot for greater volume matrix with temperature varying throughout, especially end-to-end.
 
   / Comparing different approaches to emissions #13  
I will further research compact tractor DPF temps in the next few days. I am nearly certain DPF in my Kubota L3560 reaches soot incineration temperature solely through throttle advance to 2,200 engine rpm. In abstract it would seem logical there would be one threshold temperature at which soot would incinerate cleanly and completely within DPF. Perhaps, perhaps not.

Guys, any diesel engine equipped with a DPF uses supplemental fuel during an active regen to burn off the accumulated particulate matter. I don't know why that is even in question. If EGTs are high enough to cook off accumulated PM in the DPF on their own, you'd never see the regen light. This does occur to an extent if you are working the trade hard enough. It is called a passive regen and is 100% natural and requires zero electronic intervention.

Most dealers know very little about the emissions systems on the tractors they sell. Even the service dept often knows very little.

Most tractors (and I believe Kubota is like this) that run common rail injection use a fuel injection event during the exhaust stroke. This sends fuel into the cylinder but without the compression stroke the fuel does not combust. It simply is pushed into the exhaust stream and down towards the DPF. Some DPFs use a separate injector to accomplish this but I do not believe that's the case with Kubota. I have yet to spot a 5th injector in the exhaust system of my 4 cylinder Kubota. It would be more costly. Besides, Kubota themselves mentions the possibility of fuel diluting crankcase oil in the owner's manual. The only way that can occur on an engine that isn't worn out is because of this additional fuel event where unburned fuel enters the combustion chamber but isn't burned.

Furthermore, I think you'll find that even a DPF equipped tractor will also have a DOC. The reason being that a DOC is designed to generate heat. If fuel doesn't combust when it is injected into a hot cylinder on the exhaust stroke, how would it combust in the DPF, which has lower temps than the engine cylinder? It won't, unless that fuel is oxidized in the DOC, which is what it is designed to do.

Some Kubota engines may utilize a DOC, DPF, and an EGR system, which is likely cooled. I believe my MX series tractor has a cooled EGR - I could be wrong, but upon visual inspection that's what it appears to have. There are more emissions targets than "just" particulate matter. A big one is NOx...that's what got VW into so much trouble with their TDI engines. Cooled exhaust end gases recycled into the intake causes fewer NOx emissions to form. None of these lower HP tractors utilize SCR with DEF, so NOx needs to be controlled through EGR.

Less than 26HP is able to meet TierIV Final with no changes...that's why a B2601 or an L2501 are still mechanically injected, indirectly, with zero emissions controls on them whatsoever.
 
   / Comparing different approaches to emissions #14  
The US emission standards were established in 2004. Emissions are per kW-hr. The 25 HP and under could be pretty dirty but due to low power and usual low usage rates the standard for Tier 4 was 2008. It’s not that they have no control but are relatively easy to meet. My RTV900XT and GR2120 meet Tier 4 and are sooty and smelly.

My L6060 falls in another class and has EGR and DPF. The DPF plugged percentage can actually drop under high power like full speed roading. To regen it needs to be above 1200 rpm but the harder you work the tractor the better it is - according to the book. No problem here - I traded up from a L5740 for cleaner exhaust, better power with the direct injection, and improved economy also due to direct injection. After 2 years my wife and I agree one of my better purchase decisions.

My M7-171 is in the next class, has EGR, SCF, and DPF. The DOC is at the inlet of the DPF and the SCR is after the DPF. Fuel to the DOC is the little burp shown at the end of the attached injection diagram - the post injection. Note post injection is before BDC so is still in the power stroke. There are temperature sensors at the inlet to the DOC, DPF, and outlet of the DPF. I don’t know which sensor provides the DPF temp on my panel but it runs between 1100 and 1200 in regen, about 1000 under a good load. Actually it has 2 EGR valves, one for high power high flow rate and one for low power, low flow rate.

Overall I love driving the M7 and also servicing it except it does have about 5 gearboxes. Other than changing fluids and filters, if anything major goes wrong it’s dealer time but the emissions warranty covers all the complex stuff. The worst thing so far is I have no use for it in below zero temps so it sits snug in the shed. The RTV and L6060 get the winter work and sit in the heated garage.

IMG_0061.JPG
 
   / Comparing different approaches to emissions #15  
...Fuel to the DOC is the little burp shown at the end of the attached injection diagram - the post injection. Note post injection is before BDC so is still in the power stroke...

That last injection event (D) occurs right at the end of the power stroke because it needs to happen just as the exhaust valves are opening so that the end-gases will be effectively pushed out. If the post-injection happened after the exhaust valves opened, the fuel would not effectively move nor would it be as hot.

The first injection event your manual describes is called pilot injection. The primary purpose is noise control, although it also prevents as rapid a rise in cylinder temps which helps reduce NOx.

To put into perspective, a modern diesel pickup has 7 or 8 injection events. The timing of injection pulses has become critical to fuel consumption, soot production, NOx production, power, and noise.

As far as regens are concerned, I prefer having a separate injector external to the engine which eliminates the possibility of oil-fuel dilution.
 

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