Small Diesel Engines - Natural Aspiration vs Turbo Charged?
- Thread starter welyell
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truckdiagnostics
Platinum Member
Ok, so maybe CAT was not the right "word" still without a turbo to help move air into/through the "DPF", "would it take longer to regen than one with?
I also believe some diesel engines have SCR which I think is a CAT hence DPF fluid. Is it a filter or is it a CAT or is it a filter that uses a catalytic reaction to make it a better filter? Is it just a CAT and it doesn't filter out any soot then? Not sure if the distinction matters for my question, but I could be wrong.
Agvg
Elite Member
That on the left is the cast iron center of the turbo, the top picture is the bushing that carrying the turbo axle, one on both sides. The bushings are loose fit in the hole, no tool required to get them out. The bushings I do believe takes up som oil so they have lubrication in those short moments the turbo spinns after shutdown. The turbo wheels are so light that I don't believe it spins for many seconds with out oil.
This turbo had around 210000 km and no sign of any wear, the problem with oil use the engine had was stuck rings after very poor maintenance. And it was a diesel, and it was mine since new so it was easy to find the guilty owner
Fallon
Super Member
There are 2 main tier 4 emissions systems I'm aware of. DPF & DEF (Diesel Exhaust Fluid). DEF is urea & sprayed into the exhaust to tamp down some emissions stuff, NOX (Nitrous Oxide) if I recall. Most trucks seem to use DEF, but not tractors (at least until you get to 100+hp machines). You can have DPF & DEF systems on the same engine.
I believe SCR is just a different term for DEF, or the term for the process rather than the consumable component.
When you get down to it, an engine is just a huge air pump. Only the valves & fuel system really differentiate it from your average air compressor. A turbo will help it pump more air, but it's already pretty good at that on own.
The regen cycle on a DPF isn't about moving air through anyway. It's about heating it up to burn off the soot. You need some air & fuel to do that, but at some point more air us just going to cool it off.
truckdiagnostics
Platinum Member
Mmmm, when you force air into a fire and it burns hotter it also burns faster? So, on an engine with a turbo and they close the waste gate spooling up the turbo forcing more air through the engine. More raw fuel and air into the CAT, DPF or whatever we want to call it, I would think maybe it would regen faster than say one without?
Also, I'm thinking an air compressor is a bit different than an engine as an air compressor does not have to be concerned about the time it takes to burn fuel and consequently exhaust scavenging and the reason for a turbo. But, I digress. So, the way I see it a turbo is in the future of our smaller diesel engines. You are just not going to be able to get the efficiency needed without one.
dodge man
Super Star Member
The turbo has nothing to do with getting the DPF hotter. The turbo moves more air on the intake side not the exhaust.
truckdiagnostics
Platinum Member
understand so how are they getting it any hotter than say when it is normally running at whatever rpm they picked for a parked regen? Why close the waste gate spooling it up faster? The turbo will push air through the cylinder, between the exhaust and intake stroke. There is a period of time between these two strokes when the exhaust valve is closing the intake is opening. (valve over lap)They are both opened at the same time. The turbo forces fresh air in pushing out the exhaust. (exhaust savaging)So, if the turbo was moving more air would it not push more air into the exhaust during this period of time? Then if they inject the fuel latter in the power stoke(think I have that right) That should give them raw fuel and more air in the DPF, hence getting them more heat, faster on an engine with a turbo. Where as on one without a turbo all they could do was inject the fuel latter creating the raw fuel to burn off the soot in the DPF. I have seen separate nozzles(if memory serves me correct) injecting raw fuel directly into the DPF, but without a way to increase air flow through the DPF short of increasing engine rpms I would think it would take longer. Hence my reasoning that an engine with a turbo will have shorter regen times.
buickanddeere
Super Member
How does a turbo increase airflow through the DPF ?
truckdiagnostics
Platinum Member
inject the fuel such that not all burns and you have raw un-burned fuel, using less air and increase boost. It occurs during exhaust and intake stroke when both valves are open. That gets the fuel and air into the DPF to get it hot. Some how one way or the other you have to increase the amount of air/oxygen going into the DPF or how else how is it going to get hot enough to burn off the soot. Not all of the engines out there have an injector going into the DPF. If it was hot enough during normal operation, why then would we need a regen? They are doing it somehow?
