open vs closed egr valve

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With a closed egr more nox will build up inside your engine if i understand corectly from varius website,s.(due to lower inlet temp or something)

But less exhaust gas wil dilute the engine with a closed egr .

Now what is the best option for a healthy engine ? blocked or open for hot dirty exhaust gas that lowers nox inside the engine ?
 
All EGR does is introduce an inert gas into the combustion chamber at part throttle to reduce combustion temps (reduce NOX) and reduce pumping losses slightly.
 
But is the advantage of reduce combustion temps (reduce NOX) and reduce pumping losses worth it to let the dirty exhaustgas enter youre engine ?
 
...and to allow EGR when it's good but block it when it's bad there is a valve. So to the OP, there's a reason the valve isn't always open or always closed. Also, NOx doesn't "build up" in the engine; if flows out with the rest of the exhaust gases.
 
Why should allowing the dirty exhaust gases back into the engine be such an awful thing? Those very gases are already being created inside the engine and must continue to be created there. The dirtiness is only a problem when a design flaw allows the EGR gases to cool too rapidly before entering the engine. That can cause solids to drop out and form deposits.

This applies mainly in reference to gasoline engines. Diesels are different.
 
nice discusion ! im not sure whats best i Always thougt egr valves where pure for emmision lowering and nothing else.
 
Originally Posted By: Kees
But is the advantage of reduce combustion temps (reduce NOX) and reduce pumping losses worth it to let the dirty exhaustgas enter youre engine ?


Depends on your point of view. If you hug trees, and worry about pollution, which is not always a bad thing, then EGR is a good thing. I think a lot of younglings never experienced a big city in summer during the 70s. Nasty.

If you could keep all the carbon particulates out of the EGR system, everyone would be happy. EGR is a fundamentally good cheap system that works.
 
Originally Posted By: Clevy
The egr helps fuel economy. Make it work like its supposed to


How exactly is that? Carnot efficiency is 1-Th/Tc. The higher Th is, the better. Diluting inerts doesnt allow max combustion temperatures (that's the intent).

I would imagine that any pumping benefit would be smaller than the combustion temperature efficiency delta.
 
So we get a bit of an oily intake and the throttle body needs to be clean every once in a while. Those are very minor inconveniences when compared to advantages that EGR provides.
And with new VVT implementations the exhaust gasses never see the intake anyway. Win, win in my book.
 
Originally Posted By: KrisZ
So we get a bit of an oily intake and the throttle body needs to be clean every once in a while. Those are very minor inconveniences when compared to advantages that EGR provides.
And with new VVT implementations the exhaust gasses never see the intake anyway. Win, win in my book.


Advantages? Im not sure I see any, unless you live in CA where NOx is a real issue.
 
In the old days--70s & 80s significant part throttle seat of the pants gains could be had if you blocked EGR circulation. I blocked off EGR circulation in all of my cars at that time. Nowadays, it would be an atrocity to attempt such a thing, as the valve's function is fully integrated with computer operation.

OP: an easy way to block a vacuum actuated EGR is with the correct size ball bearing in the actuating hose. You will probably get a CHECK ENGINE light if you attempted to do so
 
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Originally Posted By: JHZR2
Originally Posted By: KrisZ
So we get a bit of an oily intake and the throttle body needs to be clean every once in a while. Those are very minor inconveniences when compared to advantages that EGR provides.
And with new VVT implementations the exhaust gasses never see the intake anyway. Win, win in my book.


Advantages? Im not sure I see any, unless you live in CA where NOx is a real issue.



Would you rather use fuel for charge cooling under part throttle conditions? Many gassers experience fuel consumption increase when the egr is blocked off. So, unless you're after top power or running a diesel engine, egr is more than just a NOx reduction device.
 
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Originally Posted By: KrisZ

Would you rather use fuel for charge cooling under part throttle conditions? Many gassers experience fuel consumption increase when the egr is blocked off. So, unless you're after top power or running a diesel engine, egr is more than just a NOx reduction device.


Despite the hatred for DI on here... That is one of the benefits.

Running rich isnt great. I personally would prefer a better reduction catalyst or even DEF type treatment, and get the max carnot efficiency out of the fuel charge. Thermodynamics dictates max combustion temp, the CAA/EPA dictates a divergence from that. Essentially throwing millions of gallons of fuel and tons of CO2 for a little NOx... EGR or not. It may cool the charge a bit, but IMO Id rather see another way to deal, so that the max thermodynamic efficiency can be gained.

Im sure folks will have umpteen reasons why they dont like that, but IMO it would be the best way to go and the cost of implementation is minimal.
 
EGR is a huge disadvantage on diesel engines because extra soot is extra abrasive to the engine, shortening life. Soot can build up in the intake manifold and cause a loss of power. Also, more frequent oil changes are needed.

On gasoline engines, EGR can be beneficial by reducing part throttle pumping losses, and gasoline engines typically produce less soot than diesels.
 
I was asking for diesel engines to be more specific for a 1991 w124 om602 diesel and a 2005 Volvo d5 engine.

Im no treehugger but i choose for the health of my engine (love nature but i know how 3e world countries dilute more then thousands of cars)

So the extra nox thats created inside the cilinders by blocking the egr does not outweigt the bad effect of the sooty smokey exhaust gas when you look at longlivety of your engine ?
 
Originally Posted By: JHZR2


Running rich isnt great. I personally would prefer a better reduction catalyst or even DEF type treatment, and get the max carnot efficiency out of the fuel charge. Thermodynamics dictates max combustion temp, the CAA/EPA dictates a divergence from that. Essentially throwing millions of gallons of fuel and tons of CO2 for a little NOx... EGR or not. It may cool the charge a bit, but IMO Id rather see another way to deal, so that the max thermodynamic efficiency can be gained.

Im sure folks will have umpteen reasons why they dont like that, but IMO it would be the best way to go and the cost of implementation is minimal.


I'd love it if little 40+ MPG vehicles got an extra allowance of NOx in return for saving CO2. But it's not a priority in this country.
 
If it's for a diesel engine, dump the EGR. You will gain some horse power and fuel economy. Just make sure you clean the intake so that it stays clean and do something with EGR cooler lines. These are usually prone to coolant leakage, so eliminating that possible failure point would be a good thing in the long run.
 
my understanding is that the quantity of exh gas involved here is very, small. based on that, IDK if reduced pumping losses is really measurable, though in theory it plays.

Also, it's only active at low throttle conditions. Idle, and just off idle. It shuts down when there is any throttle input over very light cruise (~25-30mph in our mdx). So there's no power penalty either, since it gets out of the way if the driver asks more from the engine.

at least in modern cars, I think it's a good system.
 
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