Close coupled catalyst vs underfloor

[azmio3]

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?

 

[SomptingGuy]

Minimum effort and complexity to meet local legs. Any more is going to be expensive to produce and maintain. Probably a good thing if you are a tier 1, making this stuff. Not so good if you are a car user and need to replace expensive bits every time a sensor goes out of range or some other black box component stops doing its job.

It's a shame that my next car choice will probably be based on what emissions control tech it doesn't have.

- Steve

 

[GregLocock]

What's the objection to cats near the head? why are you so desperate to get them down to the floor?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[azmio3]

too much backpressure, too much overfuelling to keep the catalyst temperature down, bigger capacity fuel injector and pump required, too many bricks required, no more exhaust tuning opportunity with the runner joined together, too many lambda sensors required, etc. The list is too long for people who works in a major automaker 8 to 7 everyday.

 

[azmio3]

Greg Locock,

Your comments seem to suggest that you know about engine aftertreatment. What is your solution to the problems that I have posted yesterday?

 

[GregLocock]

I have no direct interest in cats, I've only worked on base engine and the acoustic part of exhaust systems.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[azmio3]

Greg,

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

 

[SomptingGuy]

Any change in the layout of exhaust components will affect the sound. By the time the NVH guys get involved, packaging and basic layout of active components is defined. NVH is very unlikely to influence or reverse these decisions.

- Steve

 

[azmio3]

Steve,

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.

 

[SomptingGuy]

"not much we can do about it"

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

 

[BrianPetersen]

Also, it's a whole lot easier to comply with legal noise level limits than it is to comply with the emission limits, so if the engineers responsible for emission control say "we need this" then NVH is not going to change it.

The Mazda Skyactiv system uses a long-tube header with the catalyst at the end of it ...

 

[BrianPetersen]

arrgh, can't edit. Mazda's catalyst is not "underfloor". The exhaust manifold wraps around and the catalyst is still tied to the engine. It's as close to the engine as they can get it without interfering with the exhaust manifold tuning requirements.