| Author | Message | ||
     Andrewb |
[quote}"why, if carburetors and fuel injectors can be so well tuned, do we need a catalytic converter to finish burning the fuel that didn't get burned in the combustion chamber?" [/quote] Cam overlap? | ||
| Rick_A |
Joey...that has little to do with it. There are 4 gasses produced by combustion. Carbon monoxide, carbon dioxide, hydrocarbons, and nitrogen oxides. Hydrocarbons result from unburned fuel. More nitrogen oxides occur from lean mixtures/high combustion temperatures. CO I'm sure is pretty well known. HC contributes to smog, and NO and NO2 (NOx) contribute to smog and acid rain. CO2 results from balanced combustion. The cat. is designed to control the three harmful emissions...one of which even a 100% efficiency engine would emit. The current problem is that, when a mixture is at a ratio where it burns "clean", the combustion temps rise to produce more NOx emissions. Otherwise, you're right, we'd hardly need the things. What are you trying to say, your Fishy carb can also magically reduces emissions better then other induction systems, too? It's a carb too, ain't it? | ||
| Hootowl |
Yes, but the engine is also pulling in air, creating a vacuum in the intake on the order of 20 lbs at idle (in a car), depending on cam timing. At idle, and partial throttle angles, there is a vacuum in there. At WOT, if the CFM rating is high enough, there would be no vacuum, but that's the only time that would occur. Discounting a backfire of course... | ||
| Rick_A |
That's not a vacuum...vacuum is a generic term that doesn't apply. A true vacuum is removing the amount of air present. We're simply moving it. The piston creates the force by moving the air. It doesn't matter how high the "intake force" or velocity. It's still only under atmospheric pressure, see?...unless you're using some form of forced induction. Cam timing is another thing...overlap helps peak efficiency but can loose some of the intake charge through the exhaust at lower engine speeds. | ||
| Joey |
Rick! Seems the less I say, the more you infer. How about I just say nothing, and you tell me all about why my carburetor does not do what it is doing. | ||
| Rick_A |
The more you say, the more I know what the hell you're trying to say. I'm not saying your carb isn't working. I just doubt it works to the degree that you and the manufacturer claim. EFI in cars and EFI/CV carbs are currently the most advanced and most accurate fuel metering devices in use...unless someone shows proof otherwise. The Fish carb may very well be better than your old one...but I seriously doubt it's the best thing out there...like they claim. | ||
| Hootowl |
Yes Rick, there is a vacuum, not a PERFECT vacuum, but an area under 20 lbs less pressure than the outside. That's why a vacuum gage connected to a vacuum port on the manifold will read a vacuum. If there were no restriction at the throttle plates, then that vacuum would not exist. But there is, and it does. The air moving past the venturi creates it's own vacuum, but that's because of the venturi effect, and has nothing to do with the vacuum in the manifold, other than the fact that an increase in vacuum will move the air faster, creating more vacuum signal at the venturi. The pistons are pumping air out of the manifold at a greater rate than the air coming in at standard atmospheric pressure can replenish it. This creates a pressure differential, or vacuum. Cam timing has a direct effect on manifold vacuum at idle. This is why really bumpy cams make a car idle poorly. The overlap causes contamination of the intake charge, reducing the volume of fresh fuel and air that the cylinder will take in. Less air is pumped out of the manifold, and a lower vacuum level will be present. | ||
| Rick_A |
The vacuum gauge measures the pistons impetus on the air; the force displacing the air. Your gauge reading is a force differential created by the air displaced by the piston...but the actual air pressure is still atmospheric. Get it? It's not measure in lbs, either, but in inches of mercury. It can be used as a basic measure of engine health. Some factors affecting that reading are: Piston rings, valves, ignition system, fuel control system, etc How do you expect for there to be "space" in our atmosphere? When the piston moves...the area it displaces must fill with air. The integrity of the system is what a vacuum guage measures. | ||
| Hootowl |
They read PSI. Pounds per square inch. It's not a barometer. It measures the DIFFERENCE IN PRESSURE between the atmosphere and the plenum. Since this pressure is NEGATIVE, it is a vacuum. I am NOT implying that it is a perfect vacuum (see above), there is no such thing, even in space. Vacuum. You know, the thing that operates the vacuum advance on a distributor, or vacuum secondaries on a carburetor, or a vacuum assisted power brake system. How can you justify saying that the term vacuum does not apply to an engine? Ever create a vacuum in a bell jar in physics class? Know what you used? An air pump employing a tiny little piston. Sound familiar? | ||
| Rick_A |
It's technically not a vacuum, though. It's a pressure difference...regardless of the unit of measurement. The pressure of the moving air is atmospheric. It's a very simple concept. It can't be any other way. How many times do I need to say it? Why can't you differentiate atmospheric pressure from the pressure difference created by the piston? They are completely different things. There is no such thing as a vacuum in an engine. With your jar you're sucking air out, aren't you? Isn't an engine moving air in?? Think about it. There's vacuum gauges then there are pressure gauges. Do you even know what you're talking about? | ||
| Blake |
Rick, Please read all of the following carefully. When you are finished, please point out all my incorrect statements so that I can learn the truth. It is astounding to me, that you have absolutely no interest in trying to answer any of the questions that I have posed, yet you are perfectly satisfied to sit here and preach fluid mechanics and thermodynamics based on your simplistic assumptions and incorrect perceptions. The questions I posed to you are intended to lead you to understanding. Currently you have a bit of understanding of next to nothing related to fluid mechanics and thermodynamics. One of my questions concerned how the carburetor could become significantly cooler than the ambient air. Hans answered that one for you. It becomes cool through refrigeration via evaporative cooling. You see, when a liquid vaporizes (changes from liquid to gaseous state) it requires a relatively large amount of energy. It is why when a pot of water reaches 212oF it does not instantly all turn to steam. Additional heat (energy) is required to transform the liquid to a gas. Where does that energy get taken from? It gets taken from the surrounding liquid. When you remove energy from a liquid, it cools. So you have to add more via heating to continue the boiling/vaporization process. What is happening in the carburetor is that a lot of the gasoline is vaporizing, not all, maybe not even a majority, it depends on the conditions. One of the MAJOR parameters that affects rate of vaporization is the exposed surface area of the liquid. What has more exposed surface, a closed tank containing a gallon of gasoline, an open tank containing a gallon of gasoline, a gallon of gasoline poured onto the floor, a gallon of gasoline poured onto the floor and squeegeed into a thin film, or a gallon of gasoline sprayed into the air in the form of atomized droplets? The atomized gallon would have thousands of times more surface area than the puddle on the floor. That means that it would tend to evaporate thousands of times more quickly. Can you see how gasoline might vaporize within the intake tract? Another MAJOR factor affecting the rate of vaporization is the circulation and interaction of the ambient atmosphere (air) with the exposed surface of the liquid (gasoline). The faster the air is moving over the surface the higher the rate of vaporization. Can you see how a carburetor and intake tract present that significant accelerant promoting vaporization of the atomized fuel? Other MAJOR factor affecting the rate of vaporization are the temperature of the liquid and the pressure of the ambient atmosphere. As the gasoline that is largely at equilibrium with ambient temperature passes from higher to lower pressure vaporization is facilitated. The liquid gaosline droplets cannot instantly assimilate the temperature of the air surrounding them just as water in an ice cube tray will not instantly turn frozen. However the warm fuel does instantly respond to a drop in pressure. If the pressure drop is significant enough and/or the temperature of the gasoline droplet is high enough, it responds through vaporization until its temperature drops to below the critical point. The temperature of the carburetor itself drops because the fuel is vaporizing and in so doing taking a lot of energy (heat) from the surrounding ambient atmosphere and from the carburetor's metallic parts upon which it impinges. The temperature cannot drop so much without the significant vaporization of the fuel. This is much more evident for small throttle openings where the vacuum on the engine side of the throttle is stronger than it is for large throttle openings. As to vacuum. It is technically acceptable to refer to any pressure that is less than ambient as a "vacuum". It is a relative term in fluid mechanics and engineering. That is why we refer to certain types of pressure gauges as "vacuum" gauges. A "hard vacuum" would be one nearer a theoretically perfect vacuum. It is no big deal to pull a hard vacuum. Any syringe is capable of doing so. A perfect vacuum at sea level on earth is only about -14.7 psig (0 psia). There is one very basic rule of fluid mechanics that you may be failing to grasp... Without a pressure differential (difference in pressure), there will be no (zero) flow. If all the air in the intake were at the same pressure... no flow. If the pressure differential were low... low flow. If the pressure differential is high... high flow. Low and high are of course relative terms, but you get the idea. You are correct that aside from viscous effects, a gaseous fluid cannot be pulled, rather it must be pushed to instigate flow. Kinda the opposite of not being able to push on a rope.  However, if you instigate a volume of low pressure, a "vacuum" relative to ambient conditions, you instigate flow. The throttle is simply an air valve. Closing it blocks/impedes flow; open it and flow is virtually unobstructed. The pistons vary the volume within each cylinder. At BDC they bound a large volume; at TDC they constrain a small volume. Fill a small volume with ambient air, close the air valve allowing no more air to enter, then increase the volume to ten times its original size. Congratulations, you have generated a significant vacuum. Now take that same small volume, no valve on the inlet this time... increase volume VERY quickly... congratualtions you have for a split second, generated a significant vacuum. Remember how intake length can be tuned according to the pressure pulses to take advantage of a pseudo ram induction? Without a significant vacuum coming into play, that pressure pulse phenomenon would not exist. If you can move a solid body fast enough, you can create a hard vacuum within the open atmosphere. The initiating displacement of air and the ensuing return to equilibrium creates what is known as a sonic boom. Carburetors are indeed designed to facilitate the vaporization of fuel. That is what atomization is all about. No, most carburetors are not intended or expected to vaporize all the fuel prior to it entering the hot combustion chamber. Fuel is a highly impure liquid. I truly hope that you will reconsider your tone and also cease lecturing as an expert on science that you do not yet understand. Actually, our discussion does indeed fall under the purview of "rocket sciene." Aerospace engineering is simply a specific branch of mechanical engineering and it involves a LOT of fluid mechanics and thermodynamics. I REALLY do not want to argue about this anymore. I do in fact know what I am talking about. If you have questions, I'm happy to help you find answers to them. Here's another one to help your quest for understanding. Is gasoline a pure substance? What does the answer to that question imply? BTW, I was not born knowing this stuff. I paid lots of good money to have some smart guys teach it to me; those smart guys demanded that I spend countless hours reading, studying, and working/solving problems and then taking tests to help me gain a basic understanding of it. Once in a while they would let me ask a question or two. Often they responded with another question. Got any questions?  | ||
| Blake |
Rick, "There are 4 (classes of) gasses produced by combustion..." Wrong, there are five. You missed one. "A true vacuum is removing the amount of air present." Wrong. A vaccum describes the relative absence of matter, or... A space in which the pressure is significantly lower than atmospheric pressure. The second one applies here. "The piston creates the force by moving the air." Wrong. The piston moving creates a larger volume and thus a vacuum. The instigating force (ambient pressure) that causes flow is already there. "It doesn't matter how high the "intake force" or velocity." Wrong. Velocity and pressure/vacuum are intimately related. "The vacuum gauge measures the pistons impetus on the air; the force displacing the air." Wrong. A vacuum gauge measures the difference in pressure between a point of interest and ambient (atmospheric) pressure. Rick, A reminder. Please do follow through on your offer... So Blake, you want me to point out all the false assumptions you made? You were wrong on some key points...as well as making some pretty inaccurate representations. I'll be waiting.  I'll be recalling this particular statement while I do... "Don't try to interject "facts" based on narrow reasoning to try to prove yourself right. Just face the fact that your theory amounts to nothing." What "theory"? I have proferred no "theory" here. I simply pointed out here in the "Knowledge Vault - Engine - Caruburetion" topic that your statement asserting that gasoline would not vaporize in the carburetor was wrong. You took it ALL from there trying to defend your erroneous beliefs, while making disparaging comments concerning my presentation of the facts. "YOU do the math Blake, and tell me how it works out. I could probably do it...but I'm not gonna waste my time...'cause it ain't exactly rocket science. I'd love to see what you come up with." Are you well versed and expert in advanced calculus and partial differential equations? You may think that transient three dimensional compressible fluid flow, thermodynamics of an impure partially mixed fluid, and transient heat transfer are simple. They are FAR beyond what I am willing to demonstrate or teach to someone who like yourself is unwilling to even try to answer a few rudimentary questions. "...but atmospheric pressure vaporizes fuel so well, right? Look at the vapor bursting out of my fuel tank " That is a perfect example. If you would bother to research the phenomenon of "partial pressures" you might learn the error of your simplistic analogy. To start, you might consider what comprises the gaseous atmosphere within your fuel tank and at what pressure it exists. Then research the phenomenon of partial pressures and their effect on vaporization. "Your heated mixture theory was shown to be wrong, too. Looking at the real facts, the amount of vapor going into the combustion chamber has to be around the same rate/amount that'd evaporate normally exposed to the air. So, I see your continued nit picking as useless." What "heated mixture theory" are you talking about?  As to the evaporation, I hope I answered that in my post above re. surface area and air circulation. "Here's a little something I found to very simply answer any misgivings:" You offer an explanation of the basic function of a carburetor given to a child as technical proof that gasoline does not vaporize within the carburetor? Ooooohhhh Kayyyyyy. What can I say to refute such hard technical proof.  "Putting all the factors together it's my belief that the vaporization present occurs at or less then the normal vaporization rate for fuel in ambient conditions. Just 'cause it's moving doesn't mean it's going to vaporize at a higher rate." Your belief is wrong, and the fact that the fuel is moving relative to the airflow certainly does accelerate vaporization. | ||
| Blake |
Rick, short night, good morning! The coffee is hot and the weather outside is unusually cold for East Texas. So I'm staying inside for a while. You are very intelligent, I can tell. You remind me of a certain very smart construction manager who was self assured and very confident in his knowledge of and his expertise in his trade. On one occasion he modified a very basic and simple bolted connection to help facilitate the construction he was overseeing. He was able to ingeniously devise a way to avoid having to thread half the length of one entire long tension rod like the engineers had specified. His unique and creative solution divided each long tension rod into two tension rods that each only required threads on the very ends. Problem solved. Genius at work.  Original Design per Engineer  Revised Design per Construction Manager He damn well knew what he was talking about, he was sure of it, it wasn't rocket science, it was simple common sense... One hundred fourteen people were killed by arrogance. The construction manager had NO business assuming the professional roll of a structural engineer. He was a smart fellow, but he lacked the basic understanding of fundamental structural analysis and load path recognition. The bottom supporting nut in his revised design is subject to twice the load as that in the original design. As a result, it pulled up through the welded box beam plummeting 114 people to their deaths. Unlike that example the topic of discussion here and its consequences don't amount to a hill of beans, but your attitude is perplexing to me. You lack a basic understanding of fluid mechanics and thermodynamics, yet you feel justified to lecture on the subject and tell me, someone who is educated in the subjects, that I don't know what I'm talking about. You would do well to soften your rhetoric. It would be interesting if you were to ever become educated in these disciplines some day, to come back and see your reaction to some of the assertions and beliefs you have offered here. Like I said days ago... Fluid mechanics and thermodynamics are two of THE most non-intuitive sciences in the field of mechanical engineering, so you should not feel badly that common observations might lead to erroneous assumptions. | ||
| Lornce |
Blake, Your explanation a few panels back was very good. I know it took a considerable investment of time and effort to put that together, thanks for your trouble. Rick, When Blake contains his ego, he's actually got some good information to share. He has a good grasp of the concepts. You might consider givin him a 'little respect' on that count. Try to get along now boys! Lornce Construction Millwright - "If it wasn't for engineering, we'd all be outa' work!" | ||
| Hootowl |
I am baffled by the complete lack of comprehension on your part Rick. You don't even seem to be trying to understand. Your position seems to be, "I've already formed my opinion, so don't try to confuse me with facts." | ||
| Hootowl |
Also, a barometer is incapable of measuring a vacuum. Do you even know what you're talking about? | ||
| Court |
Uh.....that would have been at 7:05 p.m. on July 17, 1981.  | ||
| Jim_Witt |
Blake, What an unfortunate tragedy. I agree with what you're trying to get across, but in my opinion it was a piss poor design to begin with. Cheers, -JW:> | ||
| Peter |
Out of curiosity, if the construction manager had double nutted the rod under the beam, would he have brought it back to spec? PPiA | ||
| Blake |
Court, I gotta keep reminding myself... GOOGLE!!! Jim, I agree, way stupid design. It violates more than one basic tenet of good structural design. But it would have held, and in the end that is the primary issue. If the engineers had properly reviewed the final drawings, they would have caught it. Lots of culpability to go around. Lornce, Thanks for the positive feedback. I hope Rick feels the same way. I'm not mad a Rick, I'm more disappointed in my own ability to inspire him to learn. I always thought I'd make a great professor. Thought about going back to finish the masters and go all the way to doctoral many times. Maybe it is a good thing I've not persued that. I've never been a very patient man. | ||
| Jim_Witt |
My opinion of course, don't see how a double nut would do a thing. A LARGE square washer (actually a piece of plate the same width of the channels) might of helped, plus there’s no gussets inside the channels to keep them from collapsing. Like I said, it’s a piss poor design from the start. -JW:> | ||
| Hans |
Peter, another picture made clear it would not: The box beam itself was weak the weak point: Maybe even badly welded, the nut on the welded area, the brims split and were folded upward giving way to the nut. Backing plate could have helped. In the interview about the Fish carb was mentioned the point of the dependency between the richness of the mixture and the level of the gasoline in the float chamber. Communicating with the levels in the emulsification tube and whatever jets there are, the effect with accelerating would be, with an afterward laying bowl, that gasoline streams afterwards, leaving the engine starved. Braking would enrich the engine too much. That makes clear why some engines pull so much better when you open the throttle gas happy instead of nailing it at WOT: You are using the accelerating pump more sensible in that case. Instead of giving one big shot, which is souped up after only a few revolutions, you enrich the mixture during the whole acceleration. You can for fastest acceleration maybe even better keep playing with almost wide open throttle. When the float chamber is laying sideways of the jet, the effect will be minimal. Hans | ||
| Court |
>>>I gotta keep reminding myself... GOOGLE!!! Absolutley and it helped to have been present, with Belger Crane Service. | ||
| Roadrunr |
IT'S LIKE BUTTER,the way you guys slide from one topic to another and back again just to prove a point!!!DAMN I LOVE THIS SITE!.. | ||
| Rick_A |
Blake, you are truly delusional now. It's apparent to me that you've chimed in again because someone else agreed with your twisted views. Call the air movement a "vacuum" all you want...but there's a tremendous difference in vacuum as a void, and vacuum in reference to the movement of air. How short sighted can you be? In all practical senses there is no vacuum present in an engine! Even the pressure drop at the venturi is not a vacuum...the amount of air isn't reduced...it's velocity is momentarily increased relative to the surrounding air. Call it a vacuum all you want, it doesn't make a difference. I was oversimplifying the above for someone who didn't understand the most basic concepts, so nitpick that all you want, too. It's pointless. The automotive industry in general makes it a point not to call the air movement in an engine a vacuum for obvious reasons...because it is misleading. Your original argument was based on the temperature being higher and pressure significantly lower. Now, I know the pressure drop in the venturi is in the magnitude of a psi to a fraction of a psi at any time, and the temp can be as much as 30 degrees lower. A cooling vapor will recondense, will it not?...it will and can to the point of being able to create ice on the throttle plate. On top of that the overall pressure value is atmospheric (take a little for friction losses and turbulence). Now, how the hell can you come up with "significantly" more vaporization as you originally assumed. About your carb plate example, the airflow is less with the throttle plate closed, genius...so the "signal" or "vacuum," as you like to call it, is relatively unchanged. A carb is known industry wide, specifically, as an atomizer. The evaporation present is small enough to not even be considered a function. Keep flattering yourself over a ridiculous farce. I was actually appalled reading the sentiments above, but after talking to some techs that literally burst out laughing at you guys, I felt a lot better. You use your education as leverage to make others believe your right. Your attempts at confusing issues and your silly assumptions are truly absurd. Your education doesn't make you a genius, guy. I also believe: 1)you probably couldn't even collect the data necessary to begin with 2)you don't want to prove yourself wrong I thought you might be enlightened some by the kiddie explanation...as they describe carb operation more accurately and precisely than you do. Do you realize the factors that have to be present for vaporization to occur with gasoline...as in high pressure and heat? Don't you think it's formulated for those specific conditions? Now Hoot, now seeing you apparent aptitude, explain to me how you could measure less than nothing with the unit of Pounds Per Square Inch. Go to your local automotive store or shop...look at what a compression gauge looks like, and what a vacuum gauge looks like. Let me know what unit of measure they use, please. I was going to link some pictures for you but couldn't find any big enough to show the unit of measure. And yes, water vapor is also produced with combustion...it's not considered a pollutant, though, is it? A space in which the pressure is significantly lower than atmospheric pressure. The second one applies here. That is GLARINGLY incorrect. How hard can it be to understand? Wrong. Velocity and pressure/vacuum are intimately related. Depends which definition of "vacuum" you're using, doesn't it? You obviously have no grasp on some key points. 1)The piston creates the "pressure difference", what you erroneously call a vacuum, because like you've stated 2)The air is at atmospheric pressure. It is moved by the pistons displacement. If you wanna call moving air at atmospheric pressure a vacuum, fine by me...but that's the vacuum definition that also applies to your vacuum cleaner...'cause you're moving air not creating a void, see? This is the part of your explanation that caused some laughter Blake. | ||
| Rick_A |
If the intake pressure was "significantly" lower than atmospheric, you'd have one highly inefficient engine! How is volumetric efficiency defined Blake? You see how your reasoning is flawed now? | ||
| Rick_A |
And this: The vacuum gauge measures the pistons impetus on the air; the force displacing the air." Wrong. A vacuum gauge measures the difference in pressure between a point of interest and ambient (atmospheric) pressure. Doesn't that basically describe my statement? | ||
| Blake |
Peter, What Hans said. In the top illustration, the two nuts supporting the red box beam are only carrying the load imparted by the beam itself (indicated by the two downward arrows acting on the beam). The load carried by the lower portion of the suspension/tension rods stays within the rods themselves; you could remove the beam and the loads acting on the tension rod would still be supported. In the revised configuration those same two nuts are forced to carry the not only the beam's loading, but also the entire load being supported by the lower suspension/tension rods. This ended up doubling the bearing load where the beam rests on the nuts. The beam was fabricated by welding two "C" section channels together. The load was so high that with a crowd of dancing partying people on the double decker walkway that the structure supported, the welded seam of the beam gave way allowing the nut to pull through. No redundant loadpath, the entire structure failed catastrophically. It's like two people hanging one obove the other onto a rope versus one person hanging onto the rope and the other person hanging onto the top persons ankles. The top person is having to support two people. Jim, Yep, poor design. Would have held. | ||
| Rick_A |
Communicating with the levels in the emulsification tube and whatever jets there are, the effect with accelerating would be, with an afterward laying bowl, that gasoline streams afterwards, leaving the engine starved. Braking would enrich the engine too much. The first half doesn't apply to all carbs, and the second is completely wrong. Most carbs have an air cut valve to prevent the lean condition that results on deceleration. | ||
| Hans |
There is the well known effect of prolonged engine braking as during mountain descents. The old fashioned two strokers with their simple carbs could even get stuck pistons because the lack of lubricating oil when throttle was closed and the engine got not enough of the gasoline/oil mixture. The extra buildup heat by a lean mixture was maybe another factor for stuck pistons. (Yes, I know that the throttle plate could never completely block the air passage, but nevertheless.) From Rick`s comment I do understand that the slight richening effect on the slow jet at braking by the inertia of the gasoline, slung back into the float bowel, is not at all important because the leaning effect of the combination high revolutions/low throttle is much greater and even so big that it needs compensation by an air cut valve. BTW, which valve is that air cut valve in our stock carbs ? My point is that the inertia of the fluid in the float bowl is another factor to take into account in my long term process to figure out why these carbs are doing so well and are compensating for so many variables. It would be easier if I could accept that "constant velocity carburettor" meant that there was a constant speed of air of the same density, temperature and water content. None of those 4 factors are constant in reality. Fact is that our Buells are pretty frugal compared to other bikes with the same power and weight. Our carbs are very complex and sophisticated beyond the basics. Hans |
