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  #1  
Old 08-24-2000, 12:42 AM
ralfmalph
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Would not the removal of a smog pump induce a hydrocarbon rich exhaust stream into the catalyst, therby increasing temperatures and possibly melting the substrate. My understanding was that the pump introduced oxygen in the exhaust ports to finish combusting the unburned warm-up fuel mixture to reduce hydrocarbon emission AND to complete the combustion upstream of the catalyst so that excess fuel poisoning and subsequent overtemp of the substrate might be avoided.

[This message has been edited by ralfmalph (edited 08-23-2000).]
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  #2  
Old 08-24-2000, 01:57 AM
mattsuzie
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Theoretically, that sounds about right. One interesting observation is that the smog pump only operates for about the 1st 30 to 60 seconds, how much of what you desribe actually take place? Obviously on Mercedes knows.

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'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)
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  #3  
Old 08-24-2000, 02:38 PM
ralfmalph
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Actually , after doing a little homework, the pump oxidizes the HCs in the catalysts and helps them heat up faster from a cold start.
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  #4  
Old 08-24-2000, 07:23 PM
mattsuzie
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From my understanding the air pump is just that. The air pump pumps air into the exhaust to enhance burning of unburnt combustion. How can the air pump "heat" up the exhaust?

I believe the theory is that the exhaust burns some of the unburnt vapor, thus sending more of of CO2 and H20 otherwise.

I think your first assessment made more sense, could be wrong though.



------------------
'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)
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  #5  
Old 08-24-2000, 09:48 PM
mattsuzie
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The smog pump goes on for less than a minute. No sustrates are going to meklt without extra air going into the exhaust (to answer your first question).

Through legalities, however, you should not mess with these emissions controls.

------------------
'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)
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  #6  
Old 08-24-2000, 11:11 PM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Quote:

"Actually , after doing a little homework, the pump oxidizes the HCs in the catalysts and helps them heat up faster from a cold start."

This description is absolutely acurate, though maybe incomplete.

For years smog pumps(A.I.R. Pumps - air injection reaction) were used continuously. They introduced air (oxygen) to the partially burned products of combustion CO and HC. The heat of the exhaust promoted a certain amount of further oxidation to CO2 and H2O. This was inefficient and catalysts were introduced to help.

This worked well BUT the catalyst and oxygen only made the creation of oxides of Nitrogen worse. Thus came the three way catalyst and the lambda oxygen control system.

The lambda system can not have extra O2 added as this is the measurement to establish stoiciometry: the exact amount of fuel and air to creat the exact amount of HC and CO2 the accepted by-product. During closed loop lambda control the NOX (oxides of nitrogen) are reduced (the chemical oposite of oxidize)by catalytic action to there base elements N2 and O2. This O2 and a small extra amount of O2 (that is fed during the lean switchoever phase of closed loop) feeds the oxidation portion of the cat to finish the combustion of unburned HC and CO>

The current action of the A.I.R Pump (or currently called: secondary air pump)is as described. It acts as the first simple oxidation action (before the cat is hot and before the O2 sensor is capable (hot). It does a sufficient job to reduce the HC content during the dirtyest performance time.

Most important it causes the catalyst to heat more quickly by creating this fire inside it. Hot air plus fuel plus slight cat activity equals great heat source.
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  #7  
Old 08-24-2000, 11:11 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Quote:

"Actually , after doing a little homework, the pump oxidizes the HCs in the catalysts and helps them heat up faster from a cold start."

This description is absolutely acurate, though maybe incomplete.

For years smog pumps(A.I.R. Pumps - air injection reaction) were used continuously. They introduced air (oxygen) to the partially burned products of combustion CO and HC. The heat of the exhaust promoted a certain amount of further oxidation to CO2 and H2O. This was inefficient and catalysts were introduced to help.

This worked well BUT the catalyst and oxygen only made the creation of oxides of Nitrogen worse. Thus came the three way catalyst and the lambda oxygen control system.

The lambda system can not have extra O2 added as this is the measurement to establish stoiciometry: the exact amount of fuel and air to creat the exact amount of HC and CO2 the accepted by-product. During closed loop lambda control the NOX (oxides of nitrogen) are reduced (the chemical oposite of oxidize)by catalytic action to there base elements N2 and O2. This O2 and a small extra amount of O2 (that is fed during the lean switchoever phase of closed loop) feeds the oxidation portion of the cat to finish the combustion of unburned HC and CO>

The current action of the A.I.R Pump (or currently called: secondary air pump)is as described. It acts as the first simple oxidation action (before the cat is hot and before the O2 sensor is capable (hot). It does a sufficient job to reduce the HC content during the dirtyest performance time.

Most important it causes the catalyst to heat more quickly by creating this fire inside it. Hot air plus fuel plus slight cat activity equals great heat source.
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  #8  
Old 08-25-2000, 09:51 AM
mattsuzie
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Not to be a stickler, but the "air" the air pumps may cause oxidation, but not the air pump (guess I was looking at this a little more stoiciometrically).. I know what you were saying though. My bad. Thanks Steve.
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