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Author Topic: What is the real func of sec air injection system?  (Read 2876 times)

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gsizoli

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What is the real func of sec air injection system?
« on: 04 February 2009, 16:25:19 »
Hi!

This quetion is addressed for mechanics.
Does anybody know what is the real function of the secondary air injection system?
As I know it's heating the cats till the operating tempearture is reached, (By feeding air into the exhaust manifold (secondary air), CO and HC are oxidized through afterburning at temperatures over 600°C to form water and carbon dioxide. The exothermal reaction also increases the exhaust gas temperature, which warms the catalyist more quickly.
) but a guy says it'"s not heating (it's heated by the exhaust gas) just blows air which mixes with the exhaust gas to protect cats from damage.
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oceansoul

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Re: What is the real func of sec air injection system?
« Reply #1 on: 04 February 2009, 17:06:39 »
i dunno what they do, but many people take them out and notice no difference
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markey mark

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Re: What is the real func of sec air injection system?
« Reply #2 on: 04 February 2009, 17:13:49 »
its to fast warm your cats to keep emmisions down ! was only for banding at the time  :y
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RobG

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Re: What is the real func of sec air injection system?
« Reply #3 on: 04 February 2009, 17:17:08 »
  The secondary air injection is a system where by air is blown into the exhaust manifolds for the first few minutes of startup, any unburnt fuel then ignites in the front pieps and the cats heat up a bit quicker.

This is done by a large blower which is mounted in the passenger side front wing, the air blows through a tube into the vac operated shut off valve mounted on the radiator (vac operated so when at Wide Open Throttle there is no air injection plus there is ECU control to via a vac valve).

Courtesy of Marks DTM Oct, 2006
« Last Edit: 04 February 2009, 17:18:10 by RobG »
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feeutfo

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Re: What is the real func of sec air injection system?
« Reply #4 on: 04 February 2009, 17:19:00 »
its only purpose is to make people post questions on here about "whats that horrible noise, whats it for, how do i get rid?" so all can give a unanimous reply.... Unplug it! Thats all it does. :-)
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Martin_1962

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Re: What is the real func of sec air injection system?
« Reply #5 on: 04 February 2009, 17:49:16 »
Usual use more energy to create less emmisions 'dangle berries'
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magnul

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Re: What is the real func of sec air injection system?
« Reply #6 on: 04 February 2009, 17:59:29 »
And what's wrong about reducing the CO and HC emissions?
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TheBoy

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Re: What is the real func of sec air injection system?
« Reply #7 on: 04 February 2009, 18:10:34 »
Quote
And what's wrong about reducing the CO and HC emissions?
It doesn't reduce CO(x) or HC though.  It reduces NO(x)
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magnul

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Re: What is the real func of sec air injection system?
« Reply #8 on: 04 February 2009, 18:15:58 »
Quote
Quote
And what's wrong about reducing the CO and HC emissions?
It doesn't reduce CO(x) or HC though.  It reduces NO(x)

Reducing CO and HC requires oxidizing conditions (as made by the secondary air). Reducing NOx requires reducing conditions (as made during the rich cycles at closed loop).
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TheBoy

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Re: What is the real func of sec air injection system?
« Reply #9 on: 04 February 2009, 18:17:30 »
Quote
Quote
Quote
And what's wrong about reducing the CO and HC emissions?
It doesn't reduce CO(x) or HC though.  It reduces NO(x)

Reducing CO and HC requires oxidizing conditions (as made by the secondary air). Reducing NOx requires reducing conditions (as made during the rich cycles at closed loop).
Actually, you're right - my mistake for not reading the question fully before reading...
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TheBoy

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Re: What is the real func of sec air injection system?
« Reply #10 on: 04 February 2009, 18:19:09 »
But to answer your Q, it doesn't really help enough with emissions to make it worthwhile.  Its removed from later UK spec cars.
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magnul

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Re: What is the real func of sec air injection system?
« Reply #11 on: 04 February 2009, 18:32:01 »
AFAIK, at least the 2.2 hasn't got it. I'm a bit curious what replaced it though. Better engine management, or some pre-cat on the down tube or something?
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TheBoy

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Re: What is the real func of sec air injection system?
« Reply #12 on: 04 February 2009, 18:34:13 »
Quote
AFAIK, at least the 2.2 hasn't got it. I'm a bit curious what replaced it though. Better engine management, or some pre-cat on the down tube or something?
nothing replaced it.
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magnul

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Re: What is the real func of sec air injection system?
« Reply #13 on: 04 February 2009, 18:39:28 »
Well, it was required to pass Euro2 emissions, so I guess something was done to still pass the later Euro emission codes.
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markey mark

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Re: What is the real func of sec air injection system?
« Reply #14 on: 04 February 2009, 18:52:43 »
Quote
Well, it was required to pass Euro2 emissions, so I guess something was done to still pass the later Euro emission codes.

yep went twin cats and dbw throttle and cpp :y
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