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Author Topic: what does this do please?  (Read 1591 times)

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gravygranules

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what does this do please?
« on: 03 February 2009, 18:23:22 »
hello chaps/ladies, my omega 2.0l is, as i write, undergoing repairs to the cam seal gasket and head gasket, but, i had a msg left on the answerphone that the EGR valve has a piece broken off...which i knew there was a part of it ''glued on'' when i bought the car..anyways....can someone tell me what an EGR valve does please?  and how it would effect the engine?....thanks v much.
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Ian_D

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Re: what does this do please?
« Reply #1 on: 03 February 2009, 18:32:26 »
EGR - Exhaust Gas Recirculation

It allows Exhaust gasses to be recycled back into the engine again (It reduces some emissions I think or something like that)

Ask them to block it up, its not needed!  :y

As for its effects, it could actually make it run better  without it :)
« Last Edit: 03 February 2009, 18:33:14 by Ian_D »
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Marks DTM Calib

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Re: what does this do please?
« Reply #2 on: 03 February 2009, 18:33:15 »
It allows exhaust gases to enter the inelt in order o reduce cylidner tempertures in an attempt to reduce NOx emmisions.

NOx is not tested as part of the MOT so I would just ignore it!
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Seth

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Re: what does this do please?
« Reply #3 on: 03 February 2009, 21:10:11 »
Well spoken Mark - spot on!
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BettyBlu

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Re: what does this do please?
« Reply #4 on: 03 February 2009, 21:35:09 »
Quote
It allows exhaust gases to enter the inelt in order o reduce cylidner tempertures in an attempt to reduce NOx emmisions.

NOx is not tested as part of the MOT so I would just ignore it!

Genuine question, would exhaust gasses not increase cylinder temps. And how does this affect the fuel air mix, surely there's little to no oxygen left in the exhaust gasses. Sorry for being thick :)
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Entwood

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Re: what does this do please?
« Reply #5 on: 03 February 2009, 21:58:22 »
Quote
Quote
It allows exhaust gases to enter the inelt in order o reduce cylidner tempertures in an attempt to reduce NOx emmisions.

NOx is not tested as part of the MOT so I would just ignore it!

Genuine question, would exhaust gasses not increase cylinder temps. And how does this affect the fuel air mix, surely there's little to no oxygen left in the exhaust gasses. Sorry for being thick :)


No, the exhaust gases contain less oxygen and replace "fresh" air.. so there is less oxygen in the cylinder;  this slows down the rate of burning of the fuel and thus reduces the cylinder temperature.

As long as sufficient oxygen is present to burn all the fuel then all the energy in the fuel is released and the power produced is the same, however the reduced flame speed means the power is produced over a slightly longer time period which affects acceleration.

This is how I understand it works .. if I'm wrong an expert will pass by and correct me shortly .. :)
« Last Edit: 03 February 2009, 21:59:28 by entwood »
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Freypal

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Re: what does this do please?
« Reply #6 on: 03 February 2009, 22:44:19 »
EGR works on the principle of PV=mRT or T=PV/mR ...

Increase the mass in the cylinder and T drops accordingly. Lower cylinder temperature reduces NOx formation.
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BettyBlu

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Re: what does this do please?
« Reply #7 on: 03 February 2009, 23:15:52 »
Quote
EGR works on the principle of PV=mRT or T=PV/mR ...

Increase the mass in the cylinder and T drops accordingly. Lower cylinder temperature reduces NOx formation.

Thanks for both explanations! I understand we're talking relative here - as in lower 'explosive' temperatures and nothing to do with air temperature before it gets to the inlet?

My vague interpretation is that this results in similar explosive pressure but over a longer period. Does this not translate to greater torque with a trade-off in power?
So removing EGR would reverse this and ideally result in less torque but more power (slightly...?)
Or has the whole she-bang got nothing at all to do with engine performance and is purely an emissions thing?
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Freypal

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Re: what does this do please?
« Reply #8 on: 04 February 2009, 10:53:59 »
EGR will have a slight effect on performance yes. If anything the pre-cylinder temperature can be slightly higher. On a forced induction car this is negated by intercoolers. In cylinder is lower due to the increase in mass and decrease in relative ratio of lean mixture / oxygen.

Under normal running, ie not wide open throttle and idle, the presence of egr will have very little impact. Advanced spark timing can overcome the slower burn, releasing more postive work done at and after TDC instead of the quick burn before TDC (negative energy work).

Hope that makes some sense! It's how i've been taught at uni haha.
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gravygranules

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Re: what does this do please?
« Reply #9 on: 04 February 2009, 19:33:23 »
wow!...thanks peeps.. :D
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BettyBlu

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Re: what does this do please?
« Reply #10 on: 04 February 2009, 22:05:51 »
All makes sense, thanks. It all serves to highlight just all the complex things going on in order to create small, powerful & efficient explosions many thousands of times a minute.
And this for years, sometimes decades and more of reliable operation in the vast majority of modern engines.
Marvellous!
« Last Edit: 04 February 2009, 22:08:23 by pSyDalila »
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Entwood

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Re: what does this do please?
« Reply #11 on: 04 February 2009, 22:14:06 »
Quote
EGR works on the principle of PV=mRT or T=PV/mR ...

Increase the mass in the cylinder and T drops accordingly. Lower cylinder temperature reduces NOx formation.


So has does the EGR increase the mass ??  Its a normally aspirated engine .. the mass in the cylinder is based on the suction created by the piston (swept volume) ... so the mass will be the same EGR or no-EGR .. the only difference is where the air mass comes from ... "fresh" air via the airbox or fresh + exhaust when the EGR is open.

If it was turbo- or super-charged you would be correct ....  :)
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magnul

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Re: what does this do please?
« Reply #12 on: 04 February 2009, 22:29:01 »
I can't understand why people are so afraid of EGR. It is inactive at WOT anyway, so it doesn't affect peak power. I addition to reducing NOx emissions, it should (at least in theory) increase efficiency and hence reduce fuel consumption.
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Abiton

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Re: what does this do please?
« Reply #13 on: 05 February 2009, 08:43:30 »
Quote
Quote
EGR works on the principle of PV=mRT or T=PV/mR ...

Increase the mass in the cylinder and T drops accordingly. Lower cylinder temperature reduces NOx formation.


So has does the EGR increase the mass ??  Its a normally aspirated engine .. the mass in the cylinder is based on the suction created by the piston (swept volume) ...

...and the throttle position, and anything introduced post-throttle  ;).

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