how a catalytic converter works
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From: Raleigh, north carolina, USA
how a catalytic converter works
There are millions of cars on the road in the United States, and each one is potentially a source of air pollution. Especially in large cities, the amount of pollution that all the cars produce together can create big problems.
To solve those problems, cities, states and the federal government create clean-air laws, and many laws have been enacted that restrict the amount of pollution that cars can produce. To keep up with these laws, automakers have made many refinements to car engines and fuel systems. To help reduce the emissions further, they have developed an interesting device called a catalytic converter, which treats the exhaust before it leaves the car and removes a lot of the pollution.
In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the calculated ideal ratio of air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1, meaning that for each pound of gasoline, 14.7 pounds of air will be burned. The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel ratio lower than 14.7).
The main emissions of a car engine are:
* Nitrogen gas (N2) - Air is 78-percent nitrogen gas, and most of this passes right through the car engine.
* Carbon dioxide (CO2) - This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air.
* Water vapor (H2O) - This is another product of combustion. The hydrogen in the fuel bonds with the oxygen in the air.
These emissions are mostly benign (although carbon dioxide emissions are believed to contribute to global warming). But because the combustion process is never perfect, some smaller amounts of more harmful emissions are also produced in car engines:
* Carbon monoxide (CO) - a poisonous gas that is colorless and odorless
* Hydrocarbons or volatile organic compounds (VOCs) - produced mostly from unburned fuel that evaporates
Sunlight breaks these down to form oxidants, which react with oxides of nitrogen to cause ground level ozone (O3), a major component of smog.
* Nitrogen oxides (NO and NO2, together called NOx) - contributes to smog and acid rain, and also causes irritation to human mucus membranes
These are the three main regulated emissions, and also the ones that catalytic converters are designed to reduce.
Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimizing the amount of catalyst required (they are very expensive).
There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure.
The Reduction Catalyst
The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:
2NO => N2 + O2 or 2NO2 => N2 + 2O2
The Oxidization Catalyst
The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:
2CO + O2 => 2CO2
But where did this oxygen come from?
The Control System
The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is an oxygen sensor mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter is. This sensor tells the engine computer how much oxygen is in the exhaust. The engine computer can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the engine computer to make sure that the engine is running at close to the stoichiometric point, and also to make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.
Other Ways to Reduce Pollution
The catalytic converter does a great job at reducing the pollution, but it can still be improved substantially. One of its biggest shortcomings is that it only works at a fairly high temperature. When you start your car cold, the catalytic converter does almost nothing to reduce the pollution in your exhaust.
One simple solution to this problem is to move the catalytic converter closer to the engine. This means that hotter exhaust gases reach the converter and it heats up faster, but this may also reduce the life of the converter by exposing it to extremely high temperatures. Most carmakers position the converter under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it.
Modified by Mad Vtack at 11:10 AM 2/11/2006
To solve those problems, cities, states and the federal government create clean-air laws, and many laws have been enacted that restrict the amount of pollution that cars can produce. To keep up with these laws, automakers have made many refinements to car engines and fuel systems. To help reduce the emissions further, they have developed an interesting device called a catalytic converter, which treats the exhaust before it leaves the car and removes a lot of the pollution.
In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the calculated ideal ratio of air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1, meaning that for each pound of gasoline, 14.7 pounds of air will be burned. The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel ratio lower than 14.7).
The main emissions of a car engine are:
* Nitrogen gas (N2) - Air is 78-percent nitrogen gas, and most of this passes right through the car engine.
* Carbon dioxide (CO2) - This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air.
* Water vapor (H2O) - This is another product of combustion. The hydrogen in the fuel bonds with the oxygen in the air.
These emissions are mostly benign (although carbon dioxide emissions are believed to contribute to global warming). But because the combustion process is never perfect, some smaller amounts of more harmful emissions are also produced in car engines:
* Carbon monoxide (CO) - a poisonous gas that is colorless and odorless
* Hydrocarbons or volatile organic compounds (VOCs) - produced mostly from unburned fuel that evaporates
Sunlight breaks these down to form oxidants, which react with oxides of nitrogen to cause ground level ozone (O3), a major component of smog.
* Nitrogen oxides (NO and NO2, together called NOx) - contributes to smog and acid rain, and also causes irritation to human mucus membranes
These are the three main regulated emissions, and also the ones that catalytic converters are designed to reduce.
Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimizing the amount of catalyst required (they are very expensive).
There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure.
The Reduction Catalyst
The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:
2NO => N2 + O2 or 2NO2 => N2 + 2O2
The Oxidization Catalyst
The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:
2CO + O2 => 2CO2
But where did this oxygen come from?
The Control System
The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is an oxygen sensor mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter is. This sensor tells the engine computer how much oxygen is in the exhaust. The engine computer can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the engine computer to make sure that the engine is running at close to the stoichiometric point, and also to make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.
Other Ways to Reduce Pollution
The catalytic converter does a great job at reducing the pollution, but it can still be improved substantially. One of its biggest shortcomings is that it only works at a fairly high temperature. When you start your car cold, the catalytic converter does almost nothing to reduce the pollution in your exhaust.
One simple solution to this problem is to move the catalytic converter closer to the engine. This means that hotter exhaust gases reach the converter and it heats up faster, but this may also reduce the life of the converter by exposing it to extremely high temperatures. Most carmakers position the converter under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it.
Modified by Mad Vtack at 11:10 AM 2/11/2006
Thread Starter
Joined: Jan 2006
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From: Raleigh, north carolina, USA
i never took credit for that? did you see me say that was my work? i was simply posting what i found out about the catalytic converter after reasearching it for a project but thanks 
Honda-Tech Member
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From: Nova Scotia, Canada
There are a lot of people out there that dont know that, specifically those who know nothing about chemistry.
Personally I did, but why criticize someone when they try to help other people learn? Stop being postwhores.
Personally I did, but why criticize someone when they try to help other people learn? Stop being postwhores.
Joined: Mar 2004
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From: Ft Wayne, IN, USA
Re: (Mad Vtack)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mad Vtack »</TD></TR><TR><TD CLASS="quote">i never took credit for that? did you see me say that was my work? i was simply posting what i found out about the catalytic converter after reasearching it for a project but thanks </TD></TR></TABLE>
It's still plagurism until you post up your sources and give credit to the original authors of the text.
Once you do that I'll give you props on the research and interesting read.
</TD></TR></TABLE>It's still plagurism until you post up your sources and give credit to the original authors of the text.
Once you do that I'll give you props on the research and interesting read.
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From: I like the tuna here
Re: (2000EM1)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2000EM1 »</TD></TR><TR><TD CLASS="quote">It's still plagurism until you post up your sources and give credit to the original authors of the text.
Once you do that I'll give you props on the research and interesting read.</TD></TR></TABLE>
bingo
Once you do that I'll give you props on the research and interesting read.</TD></TR></TABLE>
bingo
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Joined: May 2005
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Re: (2000EM1)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2000EM1 »</TD></TR><TR><TD CLASS="quote">
It's still plagurism until you post up your sources and give credit to the original authors of the text.
Once you do that I'll give you props on the research and interesting read.</TD></TR></TABLE>
who gives a f*ucking **** this a honda forum not fu*cking writing 101
It's still plagurism until you post up your sources and give credit to the original authors of the text.
Once you do that I'll give you props on the research and interesting read.</TD></TR></TABLE>
who gives a f*ucking **** this a honda forum not fu*cking writing 101
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From: I HATE, RICE
Re: (sicones)
yeah so what the fucken point? That's fucken great. Alot of people hear don't even run those, because they will destroy them really fast.
Copy and paste **** just to fucken post it.... WTF?
Copy and paste **** just to fucken post it.... WTF?
Joined: Jan 2006
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From: North Wilkesboro, NC, USA
Re: how a catalytic converter works (Mad Vtack)
I thought the information was very helpful and informative. Personally i don't care who said it. I learned something new today Some people should just stop being B!tches. If your house was on fire. . would you b!tch at the fire fighters for the way they put the fire out? Personally i would just be happy that they tried to help.
Some people should just stop being B!tches. If your house was on fire. . would you b!tch at the fire fighters for the way they put the fire out? Personally i would just be happy that they tried to help.
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From: Raleigh, north carolina, USA
Re: (sicones)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sicones »</TD></TR><TR><TD CLASS="quote">who gives a f*ucking **** this a honda forum not fu*cking writing 101</TD></TR></TABLE>
bingo
bingo
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Joined: Jan 2006
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From: Raleigh, north carolina, USA
Re: how a catalytic converter works (schlit)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by schlit »</TD></TR><TR><TD CLASS="quote">I learned in my Environmental Engineering course that the Cat converter outputs a molecule that is just as harmful to the atmosphere. Dont know the equation off the top of my head, but prof said CAT's really do not help the situation whatsoever, and there is a huge misconception about them. I'll grab my course book from work and post it up.</TD></TR></TABLE>
yes please i would be interested in hearing this.
yes please i would be interested in hearing this.
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From: Southern, MD, USA
Re: how a catalytic converter works (Mad Vtack)
Good read. Where'd you find the info?
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by schlit »</TD></TR><TR><TD CLASS="quote">I learned in my Environmental Engineering course that the Cat converter outputs a molecule that is just as harmful to the atmosphere. Dont know the equation off the top of my head, but prof said CAT's really do not help the situation whatsoever, and there is a huge misconception about them. I'll grab my course book from work and post it up.</TD></TR></TABLE>
I'd like to hear more about this as well.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by schlit »</TD></TR><TR><TD CLASS="quote">I learned in my Environmental Engineering course that the Cat converter outputs a molecule that is just as harmful to the atmosphere. Dont know the equation off the top of my head, but prof said CAT's really do not help the situation whatsoever, and there is a huge misconception about them. I'll grab my course book from work and post it up.</TD></TR></TABLE>
I'd like to hear more about this as well.
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From: Southern, MD, USA
Re: how a catalytic converter works (schlit)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by schlit »</TD></TR><TR><TD CLASS="quote">Ah ha, had the book in my home library.....
"A dual catalyst system consisting of an NO-Reducing catalyst followed by an HC/CO-oxidizing catalyst seems to be the best remedy at present. the catalyst materials are either noble metals or base metals deposited on an inert support material.
The major problems with the catalysts are their susceptibility to "poisoning" by lead phosphorus, and sulfur, and their poor wear characteristics under thermal cycling. The poisoning problem is solved by removing the lead, phosporus, and sulfur from the fuel."
Davis, Mackenzie L. and Cornwell, David A. Introduction to Environmental Engineering, Third ed. WCB McGraw-Hill, 1998. pg 541.
Take it for what its worth.</TD></TR></TABLE>
What I get out of that is that impurities/certain additives in the fuel cause a chemical reatcion to occur in the cat that isn't intended to happen. So, if we had "clean" or "blemish free" fuel cats would have have seemingly no downsides.
"A dual catalyst system consisting of an NO-Reducing catalyst followed by an HC/CO-oxidizing catalyst seems to be the best remedy at present. the catalyst materials are either noble metals or base metals deposited on an inert support material.
The major problems with the catalysts are their susceptibility to "poisoning" by lead phosphorus, and sulfur, and their poor wear characteristics under thermal cycling. The poisoning problem is solved by removing the lead, phosporus, and sulfur from the fuel."
Davis, Mackenzie L. and Cornwell, David A. Introduction to Environmental Engineering, Third ed. WCB McGraw-Hill, 1998. pg 541.
Take it for what its worth.</TD></TR></TABLE>
What I get out of that is that impurities/certain additives in the fuel cause a chemical reatcion to occur in the cat that isn't intended to happen. So, if we had "clean" or "blemish free" fuel cats would have have seemingly no downsides.
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From: I HATE, RICE
Re: how a catalytic converter works (schlit)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by schlit »</TD></TR><TR><TD CLASS="quote">I learned in my Environmental Engineering course that the Cat converter outputs a molecule that is just as harmful to the atmosphere. Dont know the equation off the top of my head, but prof said CAT's really do not help the situation whatsoever, and there is a huge misconception about them. I'll grab my course book from work and post it up.</TD></TR></TABLE>
yea it puts out sulfur, that's harmful I think. It especailly bad when your car runs really rich.
yea it puts out sulfur, that's harmful I think. It especailly bad when your car runs really rich.
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Posts: 806
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From: Ft Wayne, IN, USA
Re: (sicones)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sicones »</TD></TR><TR><TD CLASS="quote">
who gives a f*ucking **** this a honda forum not fu*cking writing 101</TD></TR></TABLE>
if he ever gets served with a subpeona, he'll give a ****.
But whatever, I didn't say it wasn't informative... but with so many people running chipped ECUs and test pipes what's the point of it?
who gives a f*ucking **** this a honda forum not fu*cking writing 101</TD></TR></TABLE>
if he ever gets served with a subpeona, he'll give a ****.
But whatever, I didn't say it wasn't informative... but with so many people running chipped ECUs and test pipes what's the point of it?
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