A catalytic converter, when operating properly, lowers the temperature at which the gases in automotive exhaust fumes burn clean:
>500°F gases burn clean with catalytic converter
>1000°F gases burn clean naturally
So a catalytic converter is unnecessary if the fumes can pass through a hot (1000°F+) section of exhaust pipe where they will ignite naturally.
How can I build such a super-heated pipe section to get a clean-burn without needing a catalytic converter?
... by natural gas? by electricity? different shape?
>How can I use more energy to do the exact same thing
how much energy is wasted "burning" exhaust gases instead of harnessing that energy somehow?
There would be no effective way to harness the heat produced by the engine that isn't negated by the added weight to the car itself.
>added weight
show your calculations
What are you going to do? Have a steam turbine running off your manifold?
There's this metal with really cool properties! It's called platinum. Check it out!
Did you know that a car with a catalytic converter burns more fuel than one without? It's by design. One without it can run a little lean in exchange for lowered power, while a car with a catalytic converter has by design to run rich, or it will overheat and damage the catalytic converter.
>a car with a catalytic converter burns more fuel than one without?
Of course, because straight piping makes more sense than wasting effort to burning off the pollution, but what if that "pollution" could be turned into energy for the car's use? Like a after-burner engine that might generate hybrid energy.
You're missing the point. Unless your catalytic converter is just clogged, its presence does not affect exhaust flow that much. The ECU literally has a routine that reads the temperature of the exhaust and adds more (unburnt) fuel to prevent cooking the catalytic converter. The power output of an engine is proportional to the amount of air that gets in, then you inject fuel to a certain ratio (air-fuel ratio). Once you reach the stoichiometric ideal ratio (14.7:1) adding more fuel will make the exhaust cooler and in turn reduce the quantity of nitrous oxide produced. The "effort" of burning off pollutants is not from pushing the exhaust through the catalytic converter, but it's from adding more fuel to the air-fuel ratio.
t. confidently incorrect
>calls out people
>doesn't elaborate
>leaves
very chad
think he's correct though, excess oxygen gets burned in the converter and ends up melting it
Exhaust on its own is much hotter when running lean because combustion is total. It also produces a lot of nitrous oxides. Adding fuel will make the combustion colder and less violent, with the trade-off of additional fuel consumption and carbon monoxide production. A catalytic converter gets you rid of all those byproducts, but it cannot be subjected to extreme heat.
When an o2 sensor is defective, typically an ECU will run rich as a protection or it will cook the cat. This means a lot of wasted fuel. The car manufacturers assume that you are going to bring it in for maintenance. If you delete your cat and don't bypass your O2 sensor you will spend a lot more on fuel.
>running lean is hotter
midwit
They're correct though...
they litterally is not
Different dude. Yes they are correct but not for turbines. Maybe you’re a dumbass aircraft mechanic.
The frick is wrong with you guys?
How the hell does it matter? You need it to pass inspection unless you don’t and then, why care? You’re done with the fuel when it burns in the combustion chamber. Let the exhaust have it. There is nothing legal to be done about it. You could make your vehicle ultra low emissions and fail inspection for doing it. It isn’t going to add pow or efficiency to recycle trash.
>inspections
I've been driving for two decades and have never been required to have my car inspected.
Fine, so there is no reason to frick with it.
>Exhaust on its own is much hotter when running lean because combustion is total
But running stoichiometric is okay?
moron.
As long as you have enough oxygen, more fuel equals more heat. And you have this oxygen all the way up to stoichiometric. After that, it stops getting any hotter because there isn't enough oxygen. It doesn't cool down.
Let's consider combustion in a 500ml cylinder. A common size found in many cars.
Quick note on AFR: It's a mass to mass ratio. We will assume a temperature of 20C for the air which gives us a density of 1.2g/1000ml
Assuming you have 500ml of clean air in the cylinder (0.6 grams), you need 0.6/14.7 = 0.040816g of gasoline for a stoichiometric burn. This is the hottest combustion you can have in the engine.
A rich mixture can be something like 14-13.8 AFR. So we do the maths again for this. 0.6/13.8 = 0.043478g.
If you subtract the 2 values you get 0.002661934 grams. You're arguing that this ant's fart of extra gasoline has enough thermal mass to keep an engine from heating up excessively from the combustion?
Sorry mate, you're moronic.
Yes, it does. It has vaporization enthalpy, and that amont on every power stroke ends up being a factor of 10 more per second. Also thats not the only reason, in case of excess fuel there is also much more carbon monoxide, and this carbon monoxide carries the heat it could have produced out the tailpaipe, or in to the catalytic converter.
>It has vaporization enthalpy, and that amont on every power stroke ends up being a factor of 10 more per second
My dude, there's 2 zeros after the decimal. There's frickall extra mass in there. Vaporization enthalpy is not going to do jack shit when there's so little fuel to vaporize.
>in case of excess fuel there is also much more carbon monoxide, and this carbon monoxide carries the heat it could have produced out the tailpaipe, or in to the catalytic converter
Conservation of mass, tardosaurus. In my example, 0.6g of air gets mixed with 0.040816g of fuel for a stoich burn, or 0.043478g for a fuel rich burn. Whatever the frick reacts in there or not the total mass can't be any higher than the mass of the air + mass of the fuel.
Again, you are arguing that this extra 0.002661934 grams of mass (0.4% of the total air mass found in the cylinder) is enough to cool the combustion in a drastic fashion.
Youre so fricking stupid, well lean engines dont burn holes to exhaust valves and pistons. Now your "problem" is fixed. Go fricking have a nice day.
>no arguments
>ad hom
I accept your surrender
i tried to run a double check on this but can't wrap my head around gas heat capacities
why do isobaric and isochoric heat capacities start differing wildly?
That's complicated stuff. It would take me a day of writing to properly explain it all.
To make things easier we can use the assumption that the engine is a closed system and that no energy can escape the combustion chamber aside from what is wasted when the exhaust valve opens.
The second assumption made is that the engine is operating full throttle at a constant RPM. Like this I don't have to calculate exact air masses and can assume you always get the maximum amount allowed by cylinder volume.
With these in mind it becomes a simple energy calculation that we can derive from the energy density of gasoline and its specific heat.
The energy density of gasoline is 46.7MJ/kg. The specific heat capacity is 2.22 kJ/kg*K
Our stoich fuel mass, 0.040816g of gasoline from our previous example gives us a total energy of 1868J.
The rich fuel mass (0.043478g) would also give us the same energy because there's not enough oxygen to burn any more than what we could at stoich.
Assuming a combustion temperature of 2500C, the mass difference, 0.002661934g, would be able to absorb a grand total of 14.77J. A groundbreaking 0.7% of the total combustion energy.
I did not account for the latent heat of vaporization in this calculation, but even with that I doubt this absorbed heat would be able to achieve values significant enough to be noticeable outside of lab conditions.
Says the one that couldn't even wrangle an AI into not spitting out outright falsities.
Lean mixtures burn completely. So completely they even manage to "burn" some nitrogen in the process.
Also
>That tiny amount of fuel is injected 30 times per second
The extremely hot combustion also takes place 30 times per second. I don't see the point you are trying to make.
m8 even ChatGPT disagrees with you. Imagine being dumber than a bot. And that ant's fart is still a 7% difference in fuel. That tiny amount of fuel is injected 30 times per second. Overall, if there is no difference in the temperature of the exhaust, then why don't all car engines run lean then? The excess NOx will be all eliminated by the cats, no?
>not noticeable blah blah blah
Have you ever wondered how the O2 sensor on a car works?
> a car with a catalytic converter burns more fuel than one without
That's the case with pretty much all emissions shit.
>EGR
>DPF/GPF
Just frick my mileage and power delivery up, man.
vw figured it out right after they got ordered to stop selling diesels in the usa. since they had to warranty the post fix systems for 15 years they actually put effort in it with a vw tdi you really dont see much gains deleting it until you go to a bigger turbo. it has enough airflow to max a stock turbo
I don't think you get it, some emissions stuff inherently consumes more fuel because of added complexity, weight and exhaust restriction, but the cat REQUIRES the engine to add a little excess fuel in the air-fuel mix to work properly.
>harnessing heat energy from the exhaust
>what is a turbocharger
>a turbocharger
I think you mean afterburner
in the 80s they would have air injecting pumps. kind of like a bellows to increase the temps.
also this...
Simplest solution would be some type of refractory, use it for insulation around the pipe(might actually be tubing but whatever). Stainless steel tig welded bare minimum, consider alloys with higher heat resistance. You can figure out how to incorporate that. It'd be heavy, brittle, no guarantees it'll get hot enough and sounds pretty dangerous.
Another option is to buy a 1962 Ford Falcon
> f the fumes can pass through a hot (1000°F+) section of exhaust pipe where they will ignite naturally.
Isn’t this literally what an EGR system does
Clearly you have found a revolutionary insight somehow missed over the past century and this being PrepHole you cannot discount any idea so we eagerly await you revolutionizing the auto industry.
Unburdened by prior knowledge you are free to discover the undiscovered. I recommend devoting your life to this.
the purpose of a catalyst is to reduce the amount of energy required to start a reaction.
it's like, if you have a ball on a hill, and it would rather be at the bottom of the hill, but it's not going to move until you push it. if you spray lube under the ball, it means you don't have to push it as hard. the lube acts like a catalyst in this example.
yes, if you put more energy into it, it will burn without the catalyst. but it requires more energy. if you use the catalyst, you don't need as much energy. instead of tapping off heat from the engine to burn the gases, you could instead use that heat to move the car.
>yes, if you put more energy into it, it will burn without the catalyst. but it requires more energy.
Exhaust already comes out hot. Can't you just insulate it?
Equilibrium prefers NO and CO at higher temperatures. Sometimes they add a reducing agent without a catalyst. I don't think there's one that deals with CO.
this is how indutries like paint shops clean their exhaust, run it throught a huge ass gas furnace, the excess heat is used for drying the paint.
the downside is the huge gas consumption which is why every paint booth build in the last decade is running circulated air nowdays and passing it over a catalytic converter if the vocs become to high.
this is why in old paint booths you can paint without masks and in new ones you need masks.
There is so much wrong information in this thread spoken so confidently that I'm now questioning whether or not I'm the one who's wrong, so I'll just type this out just in case.
>A catalytic converter, when operating properly, lowers the temperature at which the gases in automotive exhaust fumes burn clean:
That is not entirely accurate. The logic for using a cat stems from there being no "good" AFR from an emissions standpoint. If an engine runs rich, it's spewing unburned gas out the tailpipe. If it runs at stoichiometric, the heat of combustion produces nitrogen oxides. If it runs lean, the exhaust comes out clean but the lack of fuel cooling the valves eventually fricks your engine.
>a catalytic converter is unnecessary if the fumes can pass through a hot (1000°F+) section of exhaust pipe where they will ignite naturally.
No. At lean condition, there is no fuel left to burn. At rich condition, there is no oxygen left for the fuel to react with. The fuel mixture was already well over 2000°F during the combustion stroke. Pretty much everything that's going to react already has at that point. Getting it hot again, and not even as hot as it was during initial combustion, isn't going to do anything.
A catalytic converter doesn't "burn" gas. Catalysts, by definition, take part in a chemical reaction, but are themselves unaffected by it. In this case, excess fuel in the exhaust is catalyzed into (mostly) CO2 and heat. An engine with a cat and ECU actually oscillates between slightly rich and slightly lean. Rich to keep the engine happy, lean to keep the cat from burning up.
There is currently no known alternative for a catalytic converter. From a design standpoint, nobody wants them to exist, other than the ones who make them. There are untold millions of dollars and who knows how many man-hours spent trying to come up with something else. Good luck doing any better here.
>oscillates between rich and lean with the cat acting as a buffer
thanks for that, learned something new
all i know about the subject is that one of my mates ran a gardenhose of extra air into his engine and it lowered fuel consumption
what that did to the engine is unknown cause he sold the car to the gypsies half a year later
>A catalytic converter doesn't "burn" gas... excess fuel in the exhaust is catalyzed into (mostly) CO2 and heat.
producing heat is a burn, and the rare elements used to trigger the reaction are eventually depleted, so you contradict yourself. Catalytic converter removes air pollution by a secondary reaction of the exhaust fumes themselves, not by burning any excess unburnt fuel.
This secondary burn is intriguing because it is basically a bunch of wasted energy, heat, the might have been otherwise used.
>the rare elements used to trigger the reaction are eventually depleted
A catalytic reaction is one that require an additional substance, but does not consume said substance during the reaction. It might get degraded under certain conditions, but usually it stays all there.
>producing heat is a burn,
Yes. But at a lower temperature in the presence of a catalyst.
>and the rare elements used to trigger the reaction are eventually depleted
Not consumed in the reaction.
>Not consumed in the reaction
They are "eventually depleted" even a catalyst has a limited life-span
This is akin to a human dying from cell division. It can theoretically happen but shit is going to malfunction from falling apart before depletion.
>If it runs lean, the exhaust comes out clean but the lack of fuel cooling the valves eventually fricks your engine.
So how do diesels survive? They are always (unless at full throttle) running lean. Also higher compression, higher combustion temperature. And they will outlast most consumer grade petrol engines.
>So how do diesels survive? They are always (unless at full throttle) running lean
I should have maybe clarified that a little, but the short of it is that the fact that diesels don't have to worry about flame propagation.
"Lean" in a gasoline engine generally means "only a little lean". In other words, close to stoichiometric. In turn, this means a "lean running" gasoline engine sees a maximum flame temperature close to the maximum theoretically possible for a flame fueled by air. Thus, the essential problem seen with running a gasoline engine lean. If you keep going and further reduce the amount of fuel in the mixture, the flame temperature starts to go back down. The problem is, once you get the point that this starts to make a meaningful difference, the mixture is too lean to sustain a flame front, and you get incomplete combustion. This is the fundamental reason why spark-ignition engines have to be at least close to stoichiometric in order to run at all, and the solution of "just run it lean lol" doesn't work from an efficiency/emissions standpoint.
Diesels, on the other hand, are designed to compress the charge so much that it's hot enough for fuel molecules to react spontaneously with the first oxygen it comes across. There doesn't need to be a flame front. By extension, this means that the FAR doesn't matter, at all, in terms of getting the engine to operate. You can put in as little fuel as you want, and it will combust. Diesels can, therefore, operate in the region where the resultant temperature of the charge is significantly lower than it would be near stoichiometric. In fact, diesel engines are something of the opposite of gasoline engines, in that running them too RICH will produce exhaust temperatures hot enough to cause problems.
>Also higher compression, higher combustion temperature
This actually doesn't matter in the way you might think. Peak temperature in the combustion cycle is only reached for very brief periods. The charge starts to cool down immediately as it expands. The interior surfaces of the cylinder are protected by the boundary layer of gas and their own thermal mass during the short period of time the charge is at its peak temperature. Flame temperature still determines what you're going to get in terms of unwanted byproducts, but the effective average temperature within the combustion chamber is much lower, and (barring something going wrong with the engine) the only parts that are significantly affected by this lower temperature are the valves. The rest of the parts have direct contact with something to help cool them off (either oil, coolant, or both). The valves have to rely on conduction through their stems and valve seats, neither of which are all that great. That's why valves are the most heat-sensitive parts of the engine in the first place.
>And they will outlast most consumer grade petrol engines
I mean, yeah, but most diesels (at least, in the US) are heavier-duty and built better to begin with.
>How can I build such a super-heated pipe section to get a clean-burn without needing a catalytic converter?
How about a fire hazard?
We should just all drive go karts and golf carts everywhere.
Only if we get the MarioKart power ups
>So a catalytic converter is unnecessary if the fumes can pass through a hot (1000°F+) section of exhaust pipe where they will ignite naturally.
jesus, there are some really dumb mother frickers in the world
>catalytic converter alternative
run a hose from the exhaust straight to your mouth
Modern 3-way converters contain platinum, palladium and rhodium to help burn the unburnt HC and recombind the NOx. I thought this is why the modern plugs are platinum and rhodium, in an attempt to move the catalytic reaction to inside the cylinder.
>Modern 3-way converters contain platinum, palladium and rhodium to help burn the unburnt HC and recombind the NOx. I thought this is why the modern plugs are platinum and rhodium, in an attempt to move the catalytic reaction to inside the cylinder.
I just figured modern plus were platinum because it could hold up to the sparking better... Anyone know the real reason?
Platinum has excellent corrosion resistance and handles high temperatures well. To the point that Edison originally thought that it was the best candidate for developing the incandescent light.
It's used in spark plugs because it supposedly lasts longer. I seriously doubt it's more than a marketing gimmick. A modern engine won't even see all that many spark plug changes in its lifetime, anyway, unless there's some chronic ignition/fuel mixture problem.