Bri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4 Reply 1, posted (7 years 6 months 3 weeks 1 hour ago) and read 1466 times:
In automobiles, catalytic converters use a two-step chemical process -- the famous redox (reduction, oxidation) reaction.
The most common catalyst in the first step is platinum mixed with rhodium. This first stage reduces nitrogen oxides (NO) to simple N2 and O2.
The second stage, also using platinum but usually mixed with palladium as the catalyst, oxidizes carbon monoxide (CO) to produce less-harmful CO2.
Caveat: I know nothing about the use of catalytic converters in aircraft. The gases present in automobile exhaust are functions of the fuel used and the temperatures at which it's burned. Airplanes, using different fuel and very different engines, probably don't use this system at all.
Litz From United States of America, joined Dec 2003, 1749 posts, RR: 0 Reply 2, posted (7 years 6 months 2 weeks 6 days 12 hours ago) and read 1414 times:
Quoting Bri2k1 (Reply 1): Caveat: I know nothing about the use of catalytic converters in aircraft. The gases present in automobile exhaust are functions of the fuel used and the temperatures at which it's burned. Airplanes, using different fuel and very different engines, probably don't use this system at all.
AFAIK, the exhaust of combustion in a jet engine pretty much just goes right out the back end as thrust ... putting any kind of catalytic converter on that exhaust would totally defeat the purpose of thrust, would it not?
If you ever get a close-up look at a modern jet engine, you can pretty much see right through the thing from front to back, on the LP (bypass) side. And from behind, you can see directly into the HP turbines, too, from the center core of the exhaust.
Speaking of modern jets ... other than Spirit of Delta, are there any newer jets (late 70s, early 80s design or newer) on display anywhere in the world? I guess some 747s, most likely ... but can you even see into a '47 engine from the ground?
Spirit is nice because the 767's engines are right down at "person-level", so it's easy to see into them. And yes, no catalytic converter, or any other kind of "filter" on that thing ...
The Dash-80 at the Smithsonian, I don't think would count, as the JT3D isn't a modern high-bypass engine ...
HAWK21M From India, joined Jan 2001, 31450 posts, RR: 57 Reply 3, posted (7 years 6 months 2 weeks 6 days 11 hours ago) and read 1400 times:
This Catalaytic convertor in concern is used in the Bleed inlet Ducts upstream of the FSOV [Pack valve].Its used to reduce the content of Ozone in the Bleed air used for Air Conditioning prior to distribution in the Pax cabin.Has a life of approx 12,000 cycles for the B752.
Is it frequently installed on Current Aircraft.
Prebennorholm From Denmark, joined Mar 2000, 6125 posts, RR: 55 Reply 4, posted (7 years 6 months 2 weeks 2 days 16 hours ago) and read 1286 times:
Catalytic converters are not used on aircrafts, neither on turbine nor recip engines.
As stated by Bri2k1 catalytic converters mainly convert NO into N2 and O2, and CO into CO2. (They also convert any unburned HC into H2O and CO2, that's why they are called 3-way-converters).
Since NO and CO are both unstable and rather short-lived gasses, then they are relevant to convert when generated by street traffic, but much less relevant on aircrafts.
Turbine engines produce very small amounts of CO since the burning (unlike a gasoline recip engine) takes place in an environment with vastly excess oxygen.
That the same as diesel engines which also run in street traffic without catalytic converters. Special converters have been designed for diesel engines aimed more on converting HC (and NO), but they are not in widespread use. The main issue for cleaning diesel emission is particle filters, but that's an entirely different issue. They could have been very useful on the Convair 880.
NO is an issue around airports, and therefore great effort has been made to reduce NO emission from modern turbine engines. It's not an easy issue because a general rule of thumb is that the greater the compression ratio by the HP compressor, the more NO is generated, and the lower SFC, and visa versa. Meaning low NO emission = high fuel consumption. Anyway some clever tricks combined with for instance double annular combustion chambers do shift the numbers a little sidewards.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
A/c train From United Kingdom, joined Jun 2001, 501 posts, RR: 4 Reply 7, posted (7 years 6 months 2 weeks 2 days 1 hour ago) and read 1232 times:
I think what mel is talking about is the ozone filter, usually found upstream of the pack valve, ive changed one on a 320 but never on a 757. 2 clamps and a couple of mount bolts. You need to take it out to change the pack valve on a 320.
Buzz From United States of America, joined Nov 1999, 697 posts, RR: 23 Reply 14, posted (7 years 6 months 1 week 6 days 5 hours ago) and read 1077 times:
Hi Hawk21M, Buzz here. About 20 years ago there was a time change item to replace DC-10 ozone converters, I forget what time interval was for replacing them.
I've removed the A320 converters to replace a pack valve, and I've forgotten where they live on a 757... never had to replace one there. I can't recall if the 737-300's have 'em either.
HAWK21M From India, joined Jan 2001, 31450 posts, RR: 57 Reply 15, posted (7 years 6 months 1 week 6 days 2 hours ago) and read 1063 times:
Just Checked with Alteon [Boeing].
As per their Email.
The B752 Catalytic Converter is Scheduled Maintenance Replaced after 12,000 Operational Hrs.
Its a Housing containing a Precious metal [Not specified] catalyst on a Ceramic Honeycomb substrate.The Substrate is held in the housing by a corrugated knitted wire mesh.
The Catalyatic Convertor decreases the level of Ozone through a catalytic reaction between the Ozone and the precious metal catalyst.
They state 12,000 operational hrs.Is that Flight hrs.What about Ground operational time.How would that be monitored when Packs are on.
Although one needs to be at a high Altitude to have Ozone.
Just a doubt.
A342 From Germany, joined Jul 2005, 4657 posts, RR: 4 Reply 19, posted (7 years 6 months 1 week 4 days 21 hours ago) and read 994 times:
Quoting HAWK21M (Reply 17): So how common is its use by Commercial Airlines.Considering its optional.
Sorry, I'm no expert here, I've just said what I've read in an article about cabin air (or was it in a book about Concorde ?). But I think on the Concorde, the filters weren't optional because it flew at very high altitudes where there's a lot more ozone than say at FL410.
HAWK21M From India, joined Jan 2001, 31450 posts, RR: 57 Reply 20, posted (7 years 6 months 1 week 4 days 1 hour ago) and read 957 times:
Quoting VC-10 (Reply 18): You are a Licensed Engineer aren't you? Ground ops time doesn't count, just engine runs
Easy VC...Its not a crime to Double check with others.And nor is it for an Engineer to ask questions from others.I dont think there is an Engineer that knows everything.
Maybe its the Language We use.
Many things done out here seem to be very different from those done in CAA/JAA/FAA regulatory covered Areas.eg a Definition of Snag/Incident or maybe Catergories of Licences.Out here A&C cannot touch Electricals,Instruments,Radio etc.
Quoting A342 (Reply 19): But I think on the Concorde, the filters weren't optional because it flew at very high altitudes where there's a lot more ozone than say at FL410
Any Name of the book.
Thats very Educational.
Any link to a Manufacturer of these Convertors on Aircraft.