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Exhaust pipes and "catalitic converters"


flying dog
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Ok, another dumb question:

 

I thought (yeah, dumb thing to do) that ALL engines were supposed to have exhaust pipes and the newer ones also have catalitic converters on them.

 

From what I have seen on the planes, there is the engine block, and exhaust manifold and........ nothing.

 

There is no long pipe to the back of the plane - as there is in cars from the engine to the back - and the exhaust is basically blown out just behind the engine.

 

What am I missing?

 

 

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Ok, another dumb question:I thought (yeah, dumb thing to do) that ALL engines were supposed to have exhaust pipes and the newer ones also have catalitic converters on them.

 

From what I have seen on the planes, there is the engine block, and exhaust manifold and........ nothing.

 

There is no long pipe to the back of the plane - as there is in cars from the engine to the back - and the exhaust is basically blown out just behind the engine.

 

What am I missing?

In simple terms the cat is a couple of hundred small tubes (in the form of a honeycomb) that the exhaust passes through and the material it's made from glows red hot burning all the bad stuff out of the exhaust as it passes through before it gets to little kiddies breathing it.

 

Some engines, not many, have the cat inside the exhaust manifold itself and sometimes in the short header pipe so if doing an auto conversion you should be aware of that as leaded fuel particles will eventually build up and block the cat. You will notice severe power loss before it actually stops though.

 

They are very easy to smash out, very brittle, I use a foot long bit of reo bar with a bit of a taper ground on the end and just attack it with a hammer, 4 or 5 hits usually and all the chunks can be removed. If your car is older than 10 years this is quite advisable to return some performance, albeit illegal.

 

There is mumblings in various countries about light aircraft emissions so they may be standard one day to come.

 

 

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I saw a doco on cat' converters. They use..... platimun I think ...... as the "magic" stuff. So if ever you break one (cough) you want to keep it as the platinum would be worth something.

 

It went into how hard it is to get the stuff and how it is added. Quite intersting.

 

So older planes ('moths eg) would not have cat' converters as they use leaded petrol.

 

Ok, thanks. Learned something. That's a good thing. :)

 

 

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My guess as to why planes that use unleaded aren't required to have cat converters is just because the number of those airplanes in the air and the amount they contribute to pollution is a trifle compared to the number of cars on the road. With planes that run on 100LL, obviously cat converters just won't work.

 

 

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Aircraft arnt required to meet emission control limitations set for cars

 

Catalytic converters are used only for that purpoase

 

Yes leaded fuels destroy cat converters

 

Also heavy and run VERY hot, neither of which is useful in aircraft and as Scot said the volumes of avgas used is miniscule so not a very big polluter in the big picture

 

 

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I'd like to make a point, here:

 

Catalytic converters were introduced in order to reduce the oxides of nitrogen that produce "brown smog". Unleaded fuel was introduced because leaded fuel "poisons" the catalyst - with the result that the vehicle then emits hydrogen sulphide, which is not only smelly but VERY poisonous (up there with hydrogen cyanide). However, the reason given by governments at the time, was that the lead was affecting the brains of infants. This in Britain, where they still have a proportion of lead water-pipes!

 

Brown smog is a product of big cities; Sydney used to be very bad for it in the '60s, when I was attending Sydney University. The public transport system was inadequate, and so were the roads - so it typically took me over an hour in the morning and evening rush ours, to get to & from the uni. There were tens of thousands of cars sitting bumper to bumper for at least two hours every day, with their engines idling. Too many people in one place, in short. The "fix" was - better road systems, better public transport, staggered working hours, decentralisation, car sharing, and yes, the introduction of catalytic converters. I suspect that catalytic converters probably did not play all that great a part in it; higher fuel prices meant less people could afford to sit in traffic jams by the hour.

 

We have a great tendency to fix the wrong problem, for the wrong reasons, and to tell political lies about the reasons behind it. The CO2 / global warming thing is another such, in my view. So was the Y2K business. It keeps happening.

 

 

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Unleaded fuel contains Methyl Benzine as the anti-knock agent, it is a known carcinogen. They didn't tell us that when they were trying to get rid of the leaded fuel. The catalytic converter burns off the carcinogen emissions, but it takes at least 15 minutes for the catalytic converter to get up to temperature enough to burn them off. So ... for the first 15 minutes your car belches out carcinogens.

 

So think about wipper snippers, lawn mowers, chainsaws and outboard motors ... No catalytic converters ... Carcinogenic emissions.

 

We may well be required to run catalytic converters on aircraft that run on PULP at some time. The problems will be two fold:

 

Weight and how to keep the catalytic converter hot enough (extra jacket, extra weight). Either way a problem for RAAus aircraft where we struggle with weight in any case.

 

As a bit of trivia Flyin Dog. They used to run a long exhaust and silencers on Austers during the war, but that was to keep them quiet when they snuck over the English Channel and landed in the fields of France to drop off spies.

 

 

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Today it is not suggested to warm your engine by idling. Let the oil circulate and just drive off normally. Giving it heaps would not be advised a some clearances are too large (Piston /bore) when it's cold.. It warms in about 2 kms on most modern engines, that have low engine mass and not a lot of coolant. They try to get the Converter close to the valves and some have it in each head. Oxides of nitrogen (there are several of them) react with sunlight to form the brown smog you get often around 5,000 feet. Nitrogen oxides form at high burning temperatures. The EGR (Exhaust Gas Recirculation) is supposed to deal with that by lowering burning temps (and reducing power). Nev

 

 

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