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Author Topic: Do our cars really need 'cats'?  (Read 4035 times)

Offline peppercorn

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Do our cars really need 'cats'?
« on: 23/10/2010 12:10:25 »
I think I've already answered my own question.
But it still interesting to compare, I think:

http://www.law.cornell.edu/uscode/html/uscode42/usc_sec_42_00007521----000-.html
Pollutant      Emission level*
NMHC    0.125 GPM
NOx    0.2 GPM
CO    1.7 GPM
*Emission levels are expressed in grams per mile


To compare with Honda's CVCC engine:
http://cars.about.com/od/honda/fr/civic_ictdi.htm

In 1973, Honda introduced the CVCC to the Honda Civic, the only car to satisfy
the stringent 1975 emission standards under the 1970 US Clean Air Act and the 1975
Japanese standards.  Honda achieved the US standard with regular gas and with no catalytic converter.

US and Japanese Standards 1975:
CO   HC   NOx   
Japanese Standard (g/km)2100.25120
Original Muskie Standard (g/km)2110.25193

The original CVCC engine adds a small auxiliary combustion chamber located in the cylinder head (Figure 6.4). A rich fuel mixture is supplied to this auxiliary combustion chamber through its own intake passage and carburettor, and an extremely lean mixture is supplied to the main combustion chamber through its own intake passage and carburettor. The rich mixture is ignited by a spark plug in the auxiliary chamber, and the flame spreads through a torch opening to the lean mixture in the main chamber, ensuring reliable and complete combustion.14 The geometry and timing is optimized to achieve a balance of power, fuel economy, emissions, durability, and reliability.

The result was a stable, slow burn with a peak temperature low enough to minimize the formation of oxides of nitrogen, and a mean temperature held high enough and long enough to reduce carbon monoxide and hydrocarbon emissions.

Unlike emission controls based on chemical catalysts that deteriorate with use, the CVCC was designed to maintain low emissions for the life of the engine.


IMO Damn interesting solution by Honda in the early '70s.


 

Offline peppercorn

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Do our cars really need 'cats'?
« Reply #1 on: 09/11/2010 11:02:39 »
On a related note: Do LPG power cars need 'Cats'?

I mean if one was sold that was not dual-fuel (LPG only, no petrol backup).
 

Offline Don_1

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Do our cars really need 'cats'?
« Reply #2 on: 09/11/2010 11:31:30 »
As I see it, CATS are self defeating. They increase fuel consumption and don't actually reduce the hideous output of the engine, merely trap it. It is still there and needs to be dealt with. Lean burn seems a far better solution to the problem.
 

Offline peppercorn

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Do our cars really need 'cats'?
« Reply #3 on: 09/11/2010 11:52:09 »
As I see it, CATS are self defeating. They increase fuel consumption and don't actually reduce the hideous output of the engine, merely trap it. It is still there and needs to be dealt with. Lean burn seems a far better solution to the problem.

Don, I think they do deal with it (the pollution) by changing the unwanted chemicals into safe(r) ones.  Unfortunately, making and recycling the CATs is no a completely clean process either, plus they don't work until the vehicle exhaust has warmed up somewhat.

Having clean combustion to start with would, of course, be much better all round.
 

SteveFish

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Do our cars really need 'cats'?
« Reply #4 on: 10/11/2010 01:37:36 »
The Honda engine is nifty, but I am very curious about how all the emission standards work. A well set up 1.5 liter 4 cylinder can be easily set up to get 45 mpg (sorry about the mixed units, but I didn't take the time to make conversions because this isn't important for the question, and I am lazy). In comparison a big, heavy, luxury car or large SUV might get 1/4 the mileage with an engine that is 3 times the displacement. If they are both held to the same standard, grams/mile or whatever, are the big cars that much more efficient with regard to pollutants? Is this the reason for catalytic converters? Steve
 

Offline peppercorn

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Do our cars really need 'cats'?
« Reply #5 on: 11/11/2010 10:51:57 »
Is this the reason for catalytic converters?

I would suggest that non-CO2 emissions can not simply be equated to MPG. Of course there will be a rough correlation in general, but currently CATs do reform the leftover poisonous pollutants.

The figures for Emissions in 1972 are way off what is expected now and I assume that is why we can't rely on pure cylinder efficiency alone and hence need CATs.  There seems to be (very simplistically) a battle in emission terms between keeping HC/CO low against keeping NOx low (as measured post-combustion), this apparently makes 3-way CATs a necessity (at present).


The Honda engine is nifty, but I am very curious about how all the emission standards work. A well set up 1.5 liter 4 cylinder can be easily set up to get 45 mpg[US]

w w w . t d i c l u b . c o m / m i s c / c o n v e r  s i o n s . h t m l
- tells me that 45mpg(US) is 5.23 l/100km or 54mpg(imp).
The new 85bhp Fiat 500 Twin Air consumes an average of 4.1 l/100km (57.4MPG-US) - not bad in my book, though still not quite as good as a Diesel.
{Of course I don't know what your efficient litre and a half motor is theoretically getting BHP-wise (to confuse matters further I'm led to believe that US fuel is less powerful-?), but 85bhp would be fine in Europe. ::)}
« Last Edit: 11/11/2010 11:11:32 by peppercorn »
 

SteveFish

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Do our cars really need 'cats'?
« Reply #6 on: 11/11/2010 16:32:42 »
Peppercorn:

I am just very suspicious regarding US emission laws that put a small, economical, car model on par with a monster fake hummer. If I get some time I am going to look at the recent X-Prize design to see what they did. On the other hand, I lost my time somewhere.

Steve
 

Offline peppercorn

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Do our cars really need 'cats'?
« Reply #7 on: 11/11/2010 17:21:10 »
Steve, Is a fake Hummer different from (supposedly real) Hummer?  Admittedly, they both sound pretty abhorrent to me!

When you say 'put on a par with', I assume you mean it seems unfair that they both have to get to the same PPM on the HCs, COs & NOx's - ?

I think we can safely assume that without CAT's the  SUVs etc wouldn't get anywhere close, whereas the compacts (is that what call them?) might almost make the CO & HC values un-CAT'ed - again,?
 

SteveFish

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Do our cars really need 'cats'?
« Reply #8 on: 11/11/2010 20:54:05 »
Peppercorn, General Motors made a monster SUV, called a Hummer, that was just a large luxury 4 door truck with a 5 liter engine. Its only relationship to a military HMMWV, or Humvee, was its general appearance.

Catalytic converters are the obvious answer to my question regarding small efficient cars versus the large inefficient ones, but because the US manufacturers negotiated the actual pollutant levels, I wonder if the allowed mix is also somehow biased to favor the big cars. steve
 

Offline Geezer

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Do our cars really need 'cats'?
« Reply #9 on: 12/11/2010 00:55:37 »
Steve,

I don't think you can say that large vehicles with large engines are inefficient in terms of their conversion of chemical energy into work and their emission of pollutants. That may have been true twenty and more years ago, but I think it is no longer the case.

For example, my Dodge truck has a 5.7L V8, but on a long journey it consumes (lowest octane) fuel at 21 miles per US gallon. That's actually the same as the Volvo wagon I had which had a 2.4L in-line 5 banger plus turbo. And, the Volvo didn't like lowest octane gas!

Of course, you might say that neither of these vehicles are particularly efficient at moving people around, but that's a different criteria. 
 

Offline peppercorn

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Do our cars really need 'cats'?
« Reply #10 on: 12/11/2010 11:02:28 »
[GM's Hummer] only relationship to a military Humvee, was its general appearance.
I had assumed they were more closely related. Thanks!

...because the US manufacturers negotiated the actual pollutant levels, I wonder if the allowed mix is also somehow biased to favor the big cars.
I cynically expect they held back the rate of reductions, but I doubt today that the EPA standards are favouring large cars over small. Of course it may have been a different story if CATs hadn't been around to clean up the mess.


For example, my Dodge truck has a 5.7L V8, but on a long journey it consumes (lowest octane) fuel at 21 miles per US gallon. That's actually the same as the Volvo wagon I had which had a 2.4L in-line 5 banger plus turbo. And, the Volvo didn't like lowest octane gas!

Wouldn't you say that 'long journey' is key phrase though, Geezer?
This statement is only comparing one quite narrow aspect of engines with completely different characteristics.
Both the truck and the Volvo, I would hazard a guess, spend much less time near their peak efficiency during the driving-cycle than a small Euro-box Diesel would.

Admittedly, since the advent of ECUs being able to switch engine operation between Stoichiometry and Lean-burn modes dynamically, even the overpowered US lumps have started to at least give a nod to efficiency ;)
 

Offline Geezer

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Do our cars really need 'cats'?
« Reply #11 on: 12/11/2010 17:13:09 »
Wouldn't you say that 'long journey' is key phrase though, Geezer?
This statement is only comparing one quite narrow aspect of engines with completely different characteristics.
Both the truck and the Volvo, I would hazard a guess, spend much less time near their peak efficiency during the driving-cycle than a small Euro-box Diesel would.

;)

The long journey aspect only makes a small difference. The truck still gets 18 mpg on short trips. Considering the truck's mass and aerodynamics, I'd say the engine was extremely efficient, despite the fact that it's only producing a mere fraction of it's peak output (350 HP) most of the time.

Of course, it does "cheat" by cutting its displacement in half and running as a 2.8L four banger when it does not need to produce a lot of power.

The Volvo's displacement is not large in relation to it's mass (built like a tank and all wheel drive), so it was probably operating quite efficiently too. (The turbocharger does nothing most of the time.)

BTW - these are US gallons.
 

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Do our cars really need 'cats'?
« Reply #11 on: 12/11/2010 17:13:09 »

 

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