Patrol 4x4 - Nissan Patrol Forum banner

1 - 20 of 47 Posts

·
Registered
nissan patrol crd
Joined
·
13 Posts
Discussion Starter #1
blocked the egr on my 2007 crd at the weekend bought the plate from aus4wd in Bayswater I drilled a 3mm hole in it and fitted it in about an hour, the interesting part of it is the lower egts, by about 50deg, the boost pressure seems about the same, I did not have any fault codes come up and it is running very well, I wondered if any one else has experienced lower egts after egr blocking.
 

·
Administrator
Y2KGUII ZD Wgn
Joined
·
48,194 Posts
I put an article about EGR in the archives when we first did them and in the paper it states that EGR cools EGT and this is generally accepted theoretical practise, but my experience was the same as yours, mine dropped by around 20c, not quite as much as yours.
 

·
Rogue
nissan gu patrol
Joined
·
20,210 Posts
I also got a ~50*C drop in EGT after EGR block. I do not agree with the theory of EGR cooling the combustion, that doesn't make sense to me.
 

·
Registered
Nissan
Joined
·
6,063 Posts
I always thought that EGR "cools" combustion temperatures but results in hotter EGT.

Theory being NOx is formed during high combustion temperatures therefore to reduce NOx you need cooler combustion temperatures.

Its counter intuitive but I suspect that higher combustion temperatures means more energy is used to push the piston down i.e more efficient and therefore less heat in the final exhaust.

I have done a spiel on this before on the forum I will see if I can find it.

http://www.patrol4x4.com/forum/niss...w-diesel-ip-timing-affects-performance-44812/

Its more about injection timing but I think the logic applies to EGR.

Cheers

Justin
 

·
Rogue
nissan gu patrol
Joined
·
20,210 Posts
Would EGR slow the combustion as to lengthen the diesel burn time therefore less thermal-kinetic energy transfer and higher seen EGTs due to no/less cooling time during a stroke?

I'm not sure if I'm explaining my theory properly. But due to a percentage of pre-combustion gas being taken up by the inhert recirculated exhaust gases in lieu of oxygenated atmospheric gas, it therefore slows the fuel burn due to the lagged incidence of oxygen/fuel/flame mixture in the combustion. So during a stroke cycle, rather than having a faster hotter burn straight after injection followed by a period of finishing the stroke cycle that gives time for the burnt gases to cool prior to leaving the cylinder. When EGR is introduced there is burning of the fuel longer into the stroke cycle so gases are either still burning or just hotter at exhaust stroke.

Maybe?
 

·
Registered
Nissan
Joined
·
6,063 Posts
I think you are on the right track!

What we do know is that high combustion temperatures increase NOx. FACT.

Reducing NOx is the reason for EGR in the first place. FACT

Adding EGR is to reduce NOx, ergo reduce combustion temperatures.

Somewhere in that mix you end up with hotter exhaust gas.

I also think of it like this, you put on an intercooler to reduce EGT's as the incoming charge of air is cooler than before the intercooler was added. Now instead of adding cooler air we had hot exhaust gas and this must literally flow through out the exhaust.

But in terms of combustion we are mixing dirty hot air meaning we cannot be burning the fuel air mixture that well, so the actual combustion temp is lower but the engine is effectively pumping hot exhaust through itself that gets added to the exhaust temperature.

I don't fully understand it but it has to be part of the combustion process and energy transfer.

Its very hard to explain!

Cheers

Justin
 

·
Rogue
nissan gu patrol
Joined
·
20,210 Posts
So we can agree that combustion temp and exhaust temp are exclusive? I think so and I agree with your thread Justin.

When fuel burns faster it naturally burns hotter, but has a longer time between majority combustion and exhaust allowing for cooling.

When fuel burns slower, it burns until exhausted allowing for no time for cooling.

Due to a volume of fuel being the same, there is more unburnt fuel exhausting when oxygen is reduced.

Diesels burn hotter when run rich.
 

·
Registered
Nissan
Joined
·
6,063 Posts
Actually saying they are exclusive is an excellent way of putting it!!

And hence why its totally counter intuitive.

Combustion and exhaust happen at totally different parts of the engine cycle. They are separate events that are linked, can't have one without the other, but they have energy transfer in the middle.

I shall ponder some more before I say anything else.

Cheers

Justin
 

·
Registered
nissan
Joined
·
61 Posts
isn't cooler = more efficient
when u reduce ur egt
egt = heat
heat is left over energy from the combustion
energy = power
when left over energy from the combustion force down the piston
more heat is produced thus higher egt and vice versa
ANYTHING u do to ur engine will change the timing slightly
thus higher or lower egt.
you want all/as most as ur energy focus on pushing down the prison
just because it's lower at one rev
doesn't mean it be lower all though out all the rev range
this is a very short explanation

sorry if this may be off topic and it could be wrong
 

·
Rogue
nissan gu patrol
Joined
·
20,210 Posts
No not quite. Also cooler exhaust doesn't work your turbo as well ;)
 

·
Registered
Nissan
Joined
·
6,063 Posts
The aim of EGR is to reduce NOx by reducing peak combustion temps and slowing down the burn. But the overall energy released will be more or less the same (for a similar power output). Non EGR will be a hotter quicker burn, where as with EGR the burn will be lower peak temp but will last longer. (NOx production increases rapidly above about 1500 deg C)

In theory best efficiency would be an instant burn at TDC so that all of the pressure is available for the down stroke, and minimum heat is lost through the walls as the volume (and hence wall surface area) is at a minimum at TDC. This partly explains the better efficiency without EGR. Making sure you have complete combustion (no soot) explains most of the rest of the difference.

So why the hotter exhaust with EGR - that is pretty easy to explain - EGR heats up the intake charge - and typically exhaust temp follows intake temp pretty closely. This means that the average temp over the burn will be a bit hotter with EGR - but the peak still well lower.
From my industry insider who would prefer to remain anonymous. ;)

Cheers

Justin
 

·
Registered
nissan patrol
Joined
·
449 Posts
Sooooooo, is leaving the EGR system alone a good thing. My car is less responsive in lower RPMs with the EGR blocked.
 

·
Registered
nissan patrol
Joined
·
449 Posts
I have just read another thread where a French chap blocked his EGR and he lost low down torque. Has anyone else suffered this?
 

·
Rogue
nissan gu patrol
Joined
·
20,210 Posts
The lose of low rev torque is right. I suppose the severity depends on the motor and how much EGR it is tuned to run. But it will reduce compression when blocking the EGR.

If people are concerned about gunking up their intakes, fit a catch can. Exhaust gas does not deposit oily residue, this is evident in the exhaust pipe. Its only a surface carbon deposit a couple hundred micron thick, not millimetres of gunk.
 

·
Registered
nissan patrol
Joined
·
449 Posts
Well I might unblock mine then. I would rather have the torque back.l
 

·
Rogue
nissan gu patrol
Joined
·
20,210 Posts
Just fit a catch can and you'll be fine
 

·
Registered
Joined
·
33,169 Posts
so hang on, I always read that catch can and egr block is a must do mod for your car. Now I read just put a catch can in and don't worry about egr block. I have egr plate ready to go in but now I don't know if it worth while doing. what do others think ?
 
1 - 20 of 47 Posts
Top