I think we're talking about two different things here. I don't recall the initial post speaking of fuel economy but rather emissions.

Your summation of engine efficiency is a lot of mechanical information that's yet to get to the catalytic converter. But then again, you were not speaking of catalytic converters or emissions.

Why not just drop a Bell 206 turbine in the engine bay and be done with it. While not exactly fuel efficient, they are certainly heat efficient.

Cheers,

Old Oiler

 

Emissions are directly related to fundamental thermal efficiency. Especially HC emissions. They are also related to combustion chamber temperature because you have three competing elements to any ICE's emissions: HC, CO, and NOx.

The cat is insurance. It isn't primary to good emissions. It's possible to run very clean (certainly clean enough to meet any tailpipe emissions check) without a cat assuming the engine is at full operating temperature, the fuel is sufficiently oxygenated, and the engine management is tuned to stoichiometric. All the cat does is combine any leftovers that didn't quite get fully oxidized in the original burn process. The real work cats do has diminished greatly with improvements in engine management technology, and particularly with advances in oxygen sensing capabilities making wideband sensing economical for production cars.

This certainly was not true when we were still adjusting high idle and choke pull off on carburetors...

 

this thread is so far off topic it's sick

 

Maybe so..but its got a *****in' stereo!

 

I don't understand how ceramics could increase thermal efficiency THAT much. I thought the largest portion of waste heat in an engine exits with the exhaust gases, not by radiating through the engine components.

Also, wouldn't there be a big drawback with an engine that burned that hot, even if you could avoid detonation: lots of extra NOx emissions? Which also brings me to a question about your last post: isn't one of the major functions of the cat to recombine NOx into N2 and O2? How would increasing efficiency (by means of increasing combustion temperatures) help the cat do that job?

 

It's not about burning "that hot" its about managing the heat, so, no, there won't be a lot of "extra" NOx.

No, a catalytic converter's primary function is to convert CO into CO2 and unburned HC into CO2 and H2O. The NOx function didn't even appear until they developed 3 way cats, and the primary method of controlling NOx is through EGR or (now) VVT. And despite claims of the exhaust gas "cooling" the combustion temperature, that's only a part of the story.

The real workhorse is the inert gas which is why VVT can be used to replace EGR - all you need is incomplete scavenging to achieve the same effect. VVT can do this through valve timing very easily. It also eliminates a whole host of parts including the EGR valve and all the associated vacuum plumbing required to operate the EGR.

The chart below helps understand why a five gas analyser is the ideal method of tuning an ICE. Because the effluents do different things based on richness or leanness from stoichiometric, you really need to know the whole story. Add to this your fuel's stoichiometric ratio may not be 14.7:1 if it is laced with ethanol (as many fuels are today) so the discussion turns to lambda calculation because converting lambda to gasoline numbers is pointless when the fuel is mixed. This chart is also not based on emissions after a catalytic converter and does not include EGR effect. The cat's job is to take what comes out and finish the conversion to CO2, H2O, and N2. If you've already done the yeoman's job in the combustion process, the cat just puts the finishing touch on the job. As I said before, I've seen a catless vehicle meet current emissions testing standards. You just have to be tuned right on the right fuel at the right operating temperature (and yes, it will be hot.)

 

I was with you part of the way, but some of it just went compeletely over my head... Hopefully I'll be able to follow all that before too long, haha.