Close coupled catalyst vs underfloor
Close coupled catalyst vs underfloor
(OP)
Hey guys,
I am wondering on whether anyone here has any ballpark figure in terms of HC+CO emissions or catalyst lightoff difference between close coupled catalyst and underfloor one?
I am wondering on whether anyone here has any ballpark figure in terms of HC+CO emissions or catalyst lightoff difference between close coupled catalyst and underfloor one?





RE: Close coupled catalyst vs underfloor
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Close coupled catalyst vs underfloor
The modern engines emit an order of magnitude less HC/CO/NOx than what they did prior, but for sure, not all of this is from simply relocating the catalyst. I don't know of an engine family that came with both arrangements in which the repositioning of the catalyst didn't also come along with a whole bunch of other changes that make direct comparisons futile.
Powertrain engineers are applying every trick in the book to reduce emissions, particularly cold-start emissions, and bringing the catalyst close to the engine is one of them.
Mazda's Skyactiv system is a notable modern-day exception in which they had to move the catalyst out in order to accommodate a long-tube header design. But that engine uses a lot of other emission-control trickery.
Perhaps it will help to know why you are asking the question.
RE: Close coupled catalyst vs underfloor
Nowadays, the use of turbocharger will push away the catalytic converter from the exhaust port similar to the old days naturally aspirated engines. In my view, I am questioning on how much works have been done in the past to make underfloor catalyst to still achieve the Federal -7C NMOG. Furthermore, the amount of fuel enrichment at WOT to protect the closed coupled cat is just ridiculous, I dont recall having this much of fuel enrichment in the old days.
RE: Close coupled catalyst vs underfloor
As for the fuel enrichment ... the official EPA test doesn't require full throttle operation, so it never happens during the EPA test procedure, so it doesn't affect the EPA numbers!
Maybe that's why various production cars with turbo gasoline engines aren't living up to their EPA estimates ...
RE: Close coupled catalyst vs underfloor
This goes back to my earlier question, have we exhausted the solutions to make underfloor catalyst to work for the current legislations?
RE: Close coupled catalyst vs underfloor
They must be going out of their minds trying to deal with the next generation of legislative scientific extrapolation.
Mike Halloran
Pembroke Pines, FL, USA
RE: Close coupled catalyst vs underfloor
RE: Close coupled catalyst vs underfloor
Mike Halloran
Pembroke Pines, FL, USA
RE: Close coupled catalyst vs underfloor
Mike Halloran
Pembroke Pines, FL, USA
RE: Close coupled catalyst vs underfloor
There are so many turbo engines and the catalyst is placed right after the turbine. This is where I am wondering on whether underfloor can still be used for naturally aspirated
RE: Close coupled catalyst vs underfloor
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Close coupled catalyst vs underfloor
RE: Close coupled catalyst vs underfloor
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Close coupled catalyst vs underfloor
- Steve
RE: Close coupled catalyst vs underfloor
RE: Close coupled catalyst vs underfloor
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Close coupled catalyst vs underfloor
RE: Close coupled catalyst vs underfloor
NOT having to electrically heat a catalyst is a good thing. Less to go wrong. If it were a choice between a close-coupled but not electrically heated catalyst, and an under-floor but heated catalyst, I would take the close-coupled catalyst.
RE: Close coupled catalyst vs underfloor
RE: Close coupled catalyst vs underfloor
It's a shame that my next car choice will probably be based on what emissions control tech it doesn't have.
- Steve
RE: Close coupled catalyst vs underfloor
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Close coupled catalyst vs underfloor
RE: Close coupled catalyst vs underfloor
Your comments seem to suggest that you know about engine aftertreatment. What is your solution to the problems that I have posted yesterday?
RE: Close coupled catalyst vs underfloor
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Close coupled catalyst vs underfloor
For the integrated manifold, I dont fancy the sound. Have you done any noise comparison comparing integrated manifold with the old school individual runners with underfloor catalyst? I feel that at certain frequencies, integrated manifold give strange noise
RE: Close coupled catalyst vs underfloor
- Steve
RE: Close coupled catalyst vs underfloor
From my standpoint, I had enough of all the negative points that come with close coupled catalyst. While it is true that by the time NVH come there is not much we can do about it, however things may change if we have a better solution in advance.
RE: Close coupled catalyst vs underfloor
I didn't say that. I said that the basic configuration is a fixed constraint (as is base engine calibration). NVH engineers work (very well normally) within these constraints, but cannot change them. A close-coupled cat does not directly lead to poor noise quality. There are many other ways (within the constraints) to mess that up.
- Steve
RE: Close coupled catalyst vs underfloor
The Mazda Skyactiv system uses a long-tube header with the catalyst at the end of it ...
RE: Close coupled catalyst vs underfloor