| Author | Message | ||
     Reepicheep |
Rick... If the conditions between the inlet of the carb and the inside of the cylinder are as you continually assert "atmospheric or close to atmospheric" pressures, then answer the question of *why* air chooses to enter the cylinder? And when you answer that question, answer how much of that "mystery force" would be required to move 1200cc's of air 6800 times in a minute. Thanks for the info on the automotive supertrapp by the way. Cool idea, and I may try it this spring. Bill | ||
| Rick_A |
It's extremely simple...after compression, combustion, and exhaust, on the intake stroke the intake valve is open...the piston moving downward draws the air in. Displacement is basically a measure of the ideal air capacity that can be moved, and volumetric efficiency is how full the cylinder actually gets, or how close to atmospheric pressure the cylinder is when the intake valve closes. Hans, our carbs don't have an air cut valve. The idle circuit in our carbs are capable of drawing enough fuel for deceleration. Most other applications have one. Our carbs are complicated but the same basic principals apply to all of them regardless of the amount, type, complexity of metering circuits, plates, slides, jets, etc. About CV's...that is the aim...and it's as close as can be engineered into a mechanical device, I guess. | ||
| Blake |
Darn condensing water vapor and cold temperatures kept me from the track today. First race is in two short weeks! Rick, You continue to amaze and dishearten me. You have taught me that I actually can show patience. Thanks for that. "Blake, you are truly delusional now." You are right. I must be delusional trying to have a meaningful technical discussion with an obstinate joker like you. "It's apparent to me that you've chimed in again because someone else agreed with your twisted views." No. I was curious if you had made ANY effort to learn the truth. Apparently not. "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?" I've never referred to "air movement" as a "vacuum." The movement of air would be called "flow." As stated earlier, in fluid mechanics the term "vacuum" describes a pressure significantly below ambient pressure. In our case ambient pressure is atmospheric pressure. I am not short sighted. I think I am being unbelievably patient. How many graduate fluid mechanics courses have you completed? Thermodynamics? "In all practical senses there is no vacuum present in an engine!" Of course there is. What do you think happens when you slam the throttle shut at elevated rpm? You have closed the air valve blocking almost entirely the inlet to the engine. It's not much different than plugging the end of a syringe and pulling the plunger. I'm bewildered that you cannot recognize such a simple concept. The vacuum so created in a Buell engine is strong enough to suck the oil up past the rings and throw it into the exhaust to burn. Not so much in a tight fresh engine, but definitely in a well worn one, especially when hot. "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." A vacuum is a drop in pressure below that of ambient conditions. But that is neither here nor there. Semantics nor the pertinent meaning of the word "vacuum" is not the issue. I've been repeating to you that the most powerful vacuum occurs for small throttle openings (air valve is almost closed) in the intake tract past the throttle, between throttle and engine, not at the venturi. If you cannot comprehend that, I guess I'll be forced to draw a picture. If the low pressure in the carb venturi that causes fuel to be sucked from the float bowl is not a vacuum, when would it become one? "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." Anyone who refers to any type of fluid flow (you call it "air movement"  as a "vacuum" would be incorrect. The term vacuum simply indicates a pressure below that found in ambient conditions. Air movement would correctly be called "flow." "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." That is true. You don't think 1.0 psi is a significant vacuum? A 1.0 psi (LB/IN2) vacuum acting over just one square foot of area would produce a suction force capable of lifting 144 LB. But back to the core issue... How can the temperature drop SOOO drastically with only ambient air and fuel at ambient temperature flowing through the carburetor? The reason the temperature drops is, as stated before, due to the evaporative cooling effect provided by the vaporizing gasoline. The temperature of the air/fuel charge and the carburetor through which it convects and upon which it impinges drops significantly due to the significant vaporization of fuel. "A cooling vapor will recondense, will it not?" Yes. What "vapor" do you contend is being cooled to the point of condensation? Water or gasoline? I think, through your use of the word "recondense" that you mean gasoine. That would be an erroneous assumption. Gasoline once vaporized through contact with ambient air will not recondense through it's own cooling effect. That would violate the laws of thermodynamics. Contending so is akin to arguing that you could enclose ice (solid state of water) within a container of warm ambient air, and that the ice could by melting and or sublimation cool the air to below freezing and then resolidify (refreeze) as the ambient air is so cooled. It cannot happen. It violates the laws of thermodynamics. "...it will and can to the point of being able to create ice on the throttle plate." Ice is frozen water, not frozen gasoline. What causes the condensation and freezing of water in a carburetor? Answer.... The vaporization of the gasoline (evaporative refrigeration). As stated before <sigh> transforming the state of matter from liquid to solid (and from solid to liquid for that matter) requires a significant amount of energy (heat). In the case of the vaporizing gasoline inside a carburetor that heat energy is absorbed from the air and from the interacting surfaces of the carburetor. Thus the vaporization cools the air significantly. If the incoming air is humid, water will condense as teh air temperature drops it to a point below the water vapor's saturation temperature. If the air and through convection the carburetor itself is cooled to below freezing temperatures, that same condensation will solidify into ice. That ice can stick to the throtte. You would benefit much if you would make some effort to learn about vapor pressures, and partial pressures of gasses and their effects on vaporization. Also look into Initiating a change of the state in a substance from solid to liquid and/or from liquid to gas requires a surprising amount of heat (energy) be imparted into the substance. Question: What, if anything is required, to change a substance from gasseous to liquid and/or liquid to solid? What would be the effect on the ambient atmosphere surrounding that substance or from who's midst it hhad condensed or solidified? "On top of that the overall pressure value is atmospheric (take a little for friction losses and turbulence)." Air will not flow from one point to another with no change in pressure. The faster it flows the more the pressure differential required to instigate said flow. I do not know for certain what you mean by "overall pressure value." If you are talking about the total pressure differential possible, you are correct. "Now, how the hell can you come up with "significantly" more vaporization as you originally assumed." Read my post from this morning. It is explained there. Fuel at ambient temperature and pressure is injected into and is mixed with air at less than ambient pressure. Atomized fuel has extensive surface area exposed to facilitate vaporization also with the benefit of a strong circulation/flow of air. Vaporization commences immediately upon fuel's contact with air. When the throttle is only partially open it obstructs flow and so causes another significant vacuum or pressure drop. That pressure drop facilitates further vaporization of the atomized gasoline. The air is thus cooled by the vaporization of fuel (heat for vaporization is taken from the air). As the air is cooled water vapor may condense and even freeze with some ice particles becoming attached to the chilled surfaces of the carburetor surrounding the throttle. "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." If you are talking about the vacuum or pressure drop at the venturi you would be accurate. I am not talking about the pressure drop at the venturi. I am talking about the pressure drop between the throttle and the engine. Shut the air intake valve (throttle) increase the volume of cylinder (intake stroke), you have a significant vacuum. A reduction of the airflow is what causes the vacuum. Can you see that? "A carb is known industry wide, specifically, as an atomizer. The evaporation present is small enough to not even be considered a function." Why is the carburetor designed to function as an atomizer? Answer... To facilitate vaporization of the fuel. "Keep flattering yourself over a ridiculous farce." I'm not. It is not a farce. It is simple fluid mechanics and thermodynamics. Two subjects you believe you have mastered yet refuse to learn. Gasoline commences its vaporization upon contact with air. The more volatile components do so vigorously through the huge surface area presented in an atomized condition and when exposed to fiercly circulating air and a significant drop in pressure. The less volatile constituents continue on to the combustion chamber where intense heat and violent circulation complete as much as possible the process of vaporization. "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." Ignorance is bliss and apparently it loves company. And I can only wonder how accurate might be your description of the debate as communicated to your associates. "You use your education as leverage to make others believe your right." No. I offer it, VERY rarely, as evidence of my qualifications and expertise in certain subjects. A lack of educatation offers what? Answer... The opportunity for learning. Extensive training in sciences germaine to a topic of discussion along with related professional experience lend credibility to one's statements. Corroberation of those same statements through independent and reputable technical references offers them further validity. "Your attempts at confusing issues and your silly assumptions are truly absurd." My efforts are directed towards educating not confusing. You are confused only because you adamantly cling to your mistaken beliefs, refusing to challenge them in the least. "Your education doesn't make you a genius, guy." That is true. You don't need to be a genius to understand fluids or thermo. Mainly you need to have studied and practiced them. "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" Data necessary for what??  To demonstrate the concept of vaporization of gasoline? Why should I make such an effort if you are unwilling to learn even a few simple concepts... vapor pressure, partial pressure, heat capacity...? I have all the "data" sitting on the end table next to me in the form of my thermo and fluids textbooks. "I thought you might be enlightened some by the kiddie explanation...as they describe carb operation more accurately and precisely than you do." I've not attempted to "describe carb operation"; I've described the mechanism by which fuel commences vaporization within the carburetor. "Do you realize the factors that have to be present for vaporization to occur with gasoline" Yes. "...as in high pressure and heat?" Wrong. Gasoline vaporizes, as do ALL liquids, much more readily under lower pressures. In fact, above a certain pressure specific to each pure substance, liquids will not vaporize at all, no matter how high the temperature is raised. Yes, heat is required to support vaporization/evaporation. How much heat is required to vaporize 20% by volume of one gram of gasoline? How much heat is given up by 14 grams of air as it cools from say 80oF to 60oF? Careful, you may learn something. "Don't you think it's formulated for those specific conditions?" Of course. It is formulated to vaporize very easily. Ever see someone use gasoline instead of less volatile fuel like lighter fluid or diesel to help start a fire? Stand way back and throw a stick with a burning rag on the end at the pile of brush because in just the short time it takes to walk a short distance and light the rag tipped stick, the gasoline has vaporized and in a slight breeze will cause serious friggin' hurt to anyone within its reach as the fire is applied. KAWHOOSH. Ambient temperature, ambient pressure, mass amounts of vaporization. Why doesn't the fuel in your tank evaporate/vaporize? The atmosphere inside your fuel tank is not comprised of air. I could say more, but I'm enjoying your bellicose rantings. "Partial pressure", look it up. "And yes, water vapor is also produced with combustion...it's not considered a pollutant, though, is it?" You didn't specify "four polluting gasses", you stated, "There are 4 gasses produced by combustion." Water vapor is a gas and a product of combustion. Congratulations for once again being unable to admit when you are wrong.  "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?" Not difficult to understand at all. Look it up in your dictionary; the above definition came verbatim from mine. "Depends which definition of "vacuum" you're using, doesn't it?" I'm using the one widely accepted within the sciences of fluid mechanics and thermodynamics. That would be appropriate don't you think? If you are unable to comprehend the meaning that is germane to this topic, we can call it a negative gauge pressure, or a pressure drop. Your choice. "You obviously have no grasp on some key points." LOL!!! Yeah, in Rick's world of "I believe it, so it must be true" science I am clueless and my textbooks are full of lies. "1)The piston creates the "pressure difference", what you erroneously call a vacuum," Again, vacuum = pressure less than atmospheric. "...because like you've stated 2)The air is at atmospheric pressure." Air is at atmospheric pressure... outside of the running engine. "It is moved by the pistons displacement." Nope. You had it correct before, the air entering the engine is moved by the higher pressure air behind it that pushes it into the vacuum created by the piston. "If you wanna call moving air at atmospheric pressure a vacuum, fine by me." Nope. Never did. Moving air is "flow." Vacuum is less than atmospheric pressure; it is not a flow, it is a pressure, one below that of ambient atmospheric pressure. Comprendé? "..but that's the vacuum definition that also applies to your vacuum cleaner...'cause you're moving air not creating a void, see?" Nope. A vacuum is a pressure below that of atmospheric pressure. A vacuum cleaner moves air by creating such a vacuum. "This is the part of your explanation that caused some laughter Blake." What is it they say about "The laughter of fools..."? I'm truly sorry that your stubborn pride and ego seem to prevent you from engaging in a constructive discussion. I ask once more that you please drop the attitude. | ||
| Cjmblast |
If I've learned nothing else in the debate between Rick and Blake, it's the definition of vacuum - a pressure (only a pressure, NOT air movement) below ambient pressure, which in this case is atmospheric pressure outside the running engine !! I hope someday in a conversation I'm involved in someone will ask what is vacuum, and I'll have the answer because after this debate I'll never forget ! CJM | ||
| Rempss |
I have learned a lot myself. And what I have not checked out yet to determine the actual facts that support it, I will soon know. All of this stuff is actually in books! Thanks guys, I really enjoy a discussion that prompts me to learn. Jeff | ||
| Jim_Witt |
Chris stated: If I've learned nothing else in the debate between Rick and Blake, it's the definition of vacuum ...... So Chris, what takes place when you drink a liquid from a glass via a soda straw then? BTW, I wouldn't call it a debate between Rick and Blake, more like Andy trying to explain something to Barney. S'later, -JW:>] | ||
| Lornce |
Some good stuff in there Blake. Thanks for taking the effort to explain things as well as you did. Rick, you raised some good points and *I think* may have challenged Blake to consider his explanations more carefully. But it's time for you to pay attention son! -8c today but clearish roads so I actually got to ride a Buell for a few miles. Maaan that fealt GOOOD!  | ||
| Hootowl |
From the March 2003 issue of Cycle World, page 18: The subject is detonation, by Kevin Cameron. "...this changes the nature of the unburned fuel. As it first formed, from the evaporation of fuel droplets from carburetor or fuel injector..." While talking about factors that affect the likelihood of detonation, he writes, "This includes initial inlet air temperature, the cooling effect of fuel evaporation, the temperature of the intake manifold..." | ||
| Rick_A |
Blake, what I have learned is physics as they apply to the operation of an internal combustion engine. The throttle plate, obviously controls the throttle...yes, if you closed the throttle abruptly at high rpm it would create a stronger "vacuum" as you like to refer to it, at the throttle plate for a period while decelerating. That's already been discussed. The fact of the matter, the reason people think your argument is rediculous...is that it is common knowledge that a carb is a atomizer, specifically. It seems you can't practically apply your knowledge to this situation. I still don't see any facts, number, true figures, etc, from you...and you continue to attempt challenging my position with what has been reduced to this petty argument over definitions. You've modified your position with every input I make and present it as fact...as you have from the start. I've been saying the same thing from the beginning. What makes you more credible again? Just 'cause air is moving doesn't mean it can't be at atmospheric pressure. You can compare the pressure difference, or "flow", as you are now calling it, between the outside air and that moving into the engine...fine...call that a vacuum...but it's confusing in this context. It is instigated by the pistons movement. Piston no move, air no move. Tough concept, huh? So, you're saying that air moving at a couple hundred miles an hour by the the piston can't be at atmospheric pressure, it can only be moved by atmospheric pressure??? The speed of the piston, volume of cylinder(s), and rpm are directly proportional the velocity of the air...that and atmospheric pressure are the working forces. You can measure the force created by the intake velocity to that of ambient air...that is the "vacuum" you describe. I don't see what you have to contend. Gasoline is a liquid, too...water can get to the point of freezing, yet gasoline can't remain mostly in liquid droplet form?...even after pressure begins to increase after the venturi? The venturi is a relatively small area. Mass amount of vaporization with what amount of fuel dumped on the ground and how long is it left standing in stagnant air? Fresh fuel moving though a carb is in suspension for how long before it is vaporized in a combustion chamber? Again, you present another silly example that serves no practical purpose. My world is a practical one where known and proven facts are taken into consideration. Yours is one of pride where you attempt every avenue to prove a farce...significant vaporization is not present...key word here being significant. I wholly agree that it is to a negligible extent. The truth, ultimately, is a well known, common fact, that a carb effectively functions as an atomizer only...say what you want, can, anything you can contrive, any stupid examples you can throw out...won't change that. It is moved by the pistons displacement. Nope. You had it correct before, the air entering the engine is moved by the higher pressure air behind it that pushes it into the vacuum created by the piston. Some frikkin' thing...fact here is that there is no air void, and virtually no drop in pressure in reference to the "push" of atmospheric pressure. Air will not flow from one point to another with no change in pressure. The faster it flows the more the pressure differential required to instigate said flow. I do not know for certain what you mean by "overall pressure value." If you are talking about the total pressure differential possible, you are correct. Yes, of course...that's what I've been saying... About the polluting gasses deal, I purposely left water out...as it was not pertinent to my topic. How's that wrong? You're really reaching now, aren't you? Nope. Never did. Moving air is "flow." Vacuum is less than atmospheric pressure; it is not a flow, it is a pressure, one below that of ambient atmospheric pressure. Wow...how many times was I trying to say just that? Here's some examples for you from various credible sources: One factor that effects atomization is pressure. Air pressure surrounding a droplet of fuel causes it to stay together. If you reduce that surrounding pressure, the droplet will break apart into many smaller droplets. Venturi causes such a pressure reduction. By passing the droplet through the booster venturi and the venturi shape of the throttle body, the droplet is further broken down into many smaller droplets. Two other factors that influences atomization are speed and distance. As a drop of fuel begins to travel at speed over distance, the drop breaks in half. Those two drops break into four, those four drops break again, and so forth. This process continues until the fuel reaches the cylinder. Increasing the distance that the fuel can travel before it enters the cylinder will multiply the number of times the fuel can be broken into smaller droplets. Besides the air cleaner, the venturi are the farthest part of the intake tract from each cylinder. By taking advantage of the pressure and distance properties of the venturi, fuel atomization is improved over other types of fuel injection that discharges the fuel directly into either the manifold runner or straight bore of a throttle body. Increased torque and faster smoother acceleration are the immediate results of the improved combustion efficiency achieved from thorough fuel atomization. Atomization is a simple and time proven technique that is 'standard' in the industry, but is also one of the worst ways to vaporize fuel if you want maximum combustion efficiency. There have been many ideas on how to get the best \atomization, using various mechanical devices like screens, fans and turbines. Another favorite method is to use special high pressure nozzles. I've also seen various kinds of frequency devices used to 'shake' the fuel apart. All work to some degree, but there is a specific limit on how much fuel will evaporate and this has to do directly with the thermodynamics of the fuel. Another factor is TIME; in most cases the fuel just doesn't have time to evaporate. A system was developed for generating a premixed, homogeneous charge using liquid gasoline fuel which is part of an ongoing effort to determine the effect of mixture preparation on the emissions and performance of utility engines. The mixture system developed for this work was designed with the following parameters in mind: 1) Atomization of the liquid fuel 2) Vaporization of the liquid fuel 3) Mixing of the vaporized fuel with the intake air 4) Safety Liquid fuel atomization was accomplished by forcing fuel through a sapphire orifice at moderate pressures. Vaporization was aided by heating the intake air and increasing intake charge residence time. Large and small scale mixing of the fuel and air were enhanced by inducing turbulence and increasing residence time. Safety mechanisms were included to prevent unplanned mixture ignition, relieve high pressures in system components, protect the experimenter, and enable rapid shutdown if necessary. The ability of the mixture system to produce homogenious air/fuel mixtures was verified. Carburetor heat guard In order to control the optimal atomization of the fuel in the carburetor.It is installed between the engine and the carburetor and prevents vaporization by engine heat. Another basic power factor is vaporization of the fuel. Gasoline, as with other racing fuels, will not burn in a liquid state. The gasoline must be turned into a vapor for it to burn. This process of turning gasoline into a vapor is simple evaporation. It is basically no different from setting a glass of water outside and waiting for it to dry up. In the engine, of course, evaporation happens very quickly. Engine heat and fuel atomization are the keys to accelerating the evaporation process enough to turn raw gasoline into a vapor at 8000 RPM. The process of atomization turns raw fuel flow into tiny droplets which then evaporate faster due to the larger amount of surface area presented for evaporation. The size of the fuel droplets is very important. Take a large droplet of gasoline, break it up into 10 smaller droplets, and you've increased the surface area for more efficient evaporation. The result is more fuel available to be burned and do work during combustion. There's a lot more...but I made it a point to use references factoring in vaporization and atomization. I found an interesting discussion of carbs vs. EFI for performance applications here One more, in Blake's defense: In theory, a dry flow manifold should be able to offer better fuel distribution due to the lack of fuel loss from puddling or drop out while traveling through the manifold's runners. The negative aspect of that design though, is that you are now interjecting the variable of 8 injectors to administer fuel and are hoping that the rise time and atomization pattern of all 8 injectors are equal. With a wet flow style of manifold, specifically with throttle body style injection, the design is more forgiving to injector to injector variations. If the manifold is of a particularly good design as far a distribution is concerned, then it will mask alot of atomization problems. Another area of concern with a dry flow manifold is that there is no cooling effect of the vaporizing of the fuel that takes place in a wet flow manifold, which tends to dramatically raise the charge area temperature and in many instances the charge actually cools down slightly when it enters the intake port of the head. A simple rule of thumb states, that for every 10 degrees F. that the charge air temperature escalates, the engine will lose 1% of its power output. That is the reason for the horsepower limitations that are usually discovered during magazine style testing of fuel injected vs. carbureted race engines, but never explained or identified. The cooling effect of the phenomena that is referred to as "the latent heat of vaporization" historically has given the carburetor a slight edge in maximum engine output to date. The use of a thermal barrier coating on the bottom of dry flow manifolds has proven very effective and has lessened the gap considerably. But how can you assume that vaporization has to be considerable for this cooling to happen? You have yet, to any degree, proven this. At least now we know why carbed S1W's typically make a little more power than a DDFI Thunderstormed Buell.  At least we're getting closer to actually agreeing, no? | ||
| Rick_A |
Perhaps in your infinite wisdom you can settle the debate whether there is "significant" vaporization in a carb, and to what degree, Jim??? This debate has turned into more a war of words, terms and descriptions than anything else. Blake has been wrong on at least two key points...the assumptions of the temperatures and working air pressure present. I'd call those "significant" errors. Of course, he's changed his reasoning to suit, based on one of Hans' posts. Of course, a lot of you would rather kiss his ass then acknowledge that. At least I have an idea...if you have nothing productive to add to the discussion, then by all means, shut up. | ||
| Lornce |
quoting Rick-A (how do you guys get the cool colour changes when you quote folks?) "But how can you assume that vaporization has to be considerable for this cooling to happen? You have yet, to any degree, proven this." Rick, the cooling of the intake charge air will be directly proportionate to the amount of fuel vapourized. A fixed amount of fluid (fuel in this case) requires a fixed amount of energy to change state from liquid to vapour. The energy (in this case) is coming from the heat in the intake charge air. To facilitate the fuel's change in state from fluid to vapour, heat energy in the air is consumed and the air's temp drops. The relationship between the mass of air and mass of fuel required for this to occur, remain constant within parameters of pressure. This is what's referred to as the 'latent heat of vapourization'. I'm guessing Blake has the numerical definitions for those relationships close at hand in an engineering text. Lornce | ||
| Rick_A |
I'm guessing Blake has the numerical definitions for those relationships close at hand in an engineering text. Lornce, that's all I've wanted to know/hear from the very beginning! If he can prove it is "significant", and to what numerical degree that actually is, that'd be the end of it. The other point that Blake won't acknowledge is that his entire stance on the subject has drastically changed. Originally the stance was reduced pressure+heat=significant vaporization...then it basically changed to reduced pressure&cooling=proof of significant vaporization. Gimme a break...I think if anyone deserves any credit here it's Hans...he seems to be the true voice of reason in this joint. | ||
| Lornce |
quoting me "The relationship between the mass of air and mass of fuel required for this to occur, remain constant within parameters of pressure. This is what's referred to as the 'latent heat of vapourization'." Ermmmn, just gave this another think and will have to restate that as the relationship between the mass of fuel and a given amount of energy (calories?) will remain constant. The calories, in our case, are the air's heat energy and will, of course, depend on the air's temp. Dang, now you two are gonna' have me searching google or scouring used book stores for old engineering texts.... arrrgh, Lornce Never too old... To learn something new. | ||
| Rick_A |
Oh, and hit the BBS Formatting tag and you can do all the cool stuff, too. | ||
| Lornce |
quoting rick-a "Originally the stance was reduced pressure+heat=significant vaporization...then it basically changed to reduced pressure&cooling=proof of significant vaporization." Rick, it could be suggested that the above are simply two different ways of saying the same thing. One just offers more information to support the other. I think that may be just one in a number of semantical misunderstandings that've occurred along the way in this little tete a` tete. Eh? Me? I wanna be stuck on a desert island with Joan Osborne. Later budds, Lornce zzzzzzzzzzzz | ||
| Jim_Witt |
Rick asked: Perhaps in your infinite wisdom you can settle the debate whether there is "significant" vaporization in a carb, and to what degree, Jim??? Rick, Is there significant vaporization in a carb? I’ll say NO. And to what degree, I’m not capable or smart enough to measure the significant degree. I’m quite sure means exist to more efficiently vaporize fuel to a carb by some sort of vapor generator. To be perfectly honest, I never could figure out exactly (notice the exactly) what the original question was that started the lesson Blake is giving you and I did go back 3 days worth of messages. You went on to say: This debate has turned into more a war of words, terms and descriptions than anything else. That’s what I found so amusing Rick and why I wrote my smart ass remark; the miss use of words, terminology and lack of basic physics principles. Just think how smart you could be and how well you could present yourself if you understood the war of words you describe above. Then Rick had to mention: Of course, a lot you would rather kiss his ass then acknowledge that. Hey pumpkin, you must be addressing that statement to “others” since it’s against my constitution to kiss any ones ass. Rick went on the pat his own back saying: At least I have an idea...if you have nothing productive to add to the discussion, then by all means, shut up. And what was that idea since I can’t find it (in a sentence or two)? Cheers, -JW:> | ||
| Bomber |
you guys woulda aced grad level rhetoric classes . . . . some good science hidden amungst the chest beating, though . . . . .thanks | ||
| Reepicheep |
Rick... you danced around the answer to my first question... "If the conditions between the inlet of the carb and the inside of the cylinder are as you continually assert "atmospheric or close to atmospheric" pressures, then answer the question of *why* air chooses to enter the cylinder?"
Moving a cylinder down won't do squat to flow air, unless it creates a vacuum of some sort. The answer to the question is "because the pressure in the cylinder is made to be less then the pressure in the atmosphere" And then you completely ignored my second question... "And when you answer that question, answer how much of that "mystery force" would be required to move 1200cc's of air 6800 times in a minute." Air won't flow without a pressure differential. Period. And the rate at which the air flows is directly proportional to that pressure differential. Which was *supposed* to gently lead you to the second question, which is how much vacuum does it take to flow about 1200cc's of air/fuel mixtures 6800 times in a minute (actually, now that I think if it, this is probably more like 6800 times in 4 minutes... but it does not change my point). Consider also the percentage of time throughout one "cycle" in a 4 cycle engine that the engine actually spends sucking in air. The answer is "a whole bunch of vacuum (calculated to 0 significant figures ". Which should have triggered a little light-bulb somewhere to make you think... "wow. If there is that much vacuum to make that much flow, I wonder what a mist of a volatile fluid at medium to high temperatures and such low pressures will do?". And then from there it would not have been far to get to "Wow... what is the vapor pressure of gasoline, and how long can it exist in an atomized (mist) form under a vacuum significant enough to flow around 136 liters of air in a second?" I've enjoyed the discussion though. Great depth and brought up lots of subtleties to the whole process that never occurred to me as a layman (all my engineering was electrical, I only had two token college level thermodynamics classes, and thats barely enough just to understand the basic theories and terminology). As for Blake, God bless him, an engineers job is to be right, not to be nice. They only officially become an A**hole if it turns out they were wrong about the thing they were being an A**hole about It would be nice if they never uttered a caustic word and were forever careful to gently redirect the people around them, but that don't make planes fly. And if you have never been involved in a technical discussion among engineers, this is the way it normally goes, though anectdotes and observations without attributions or an accepted theoretical model are not generally given the credibility they have here. Accepted engineering theory and mathematical models are usually the points of contention. Anything else is snake oil and a waste of everyones time. A consensus is generally reached pretty quickly, based on calculations, empirical data, or targeted testing. Everybody gets on board with the final project, then goes out for lunch and finds something else to argue about . It gets pretty hot during the discussion, but it's done when its done. Don't take anything personally. Bill | ||
| Lornce |
Okay lads, I've got a relevant question re all this.... Is there gain to be realized from wrapping the intake manifold in some sort of insulating material to prevent the manifold being heated by all the radiated energy from the surrounding heads etc.? This ought to aid in reducing intake track heat and maintaining intake charge density, no? Also, why did my bike run so strong yesterday in -8c temps if the cold intake charge allowed less fuel vapourization in the intake tract? Obviously, there must be some ideal ratio of vapourised fuel/atomised fuel/atmospheric mass to facilitate efficient combustion. Stochiometric (sp? I give up!) ratios must be more complex than a simple 14:1 air/fuel mass thing.... Oh the variables involved! Lornce | ||
| Hootowl |
Lornce, The manifold is absorbing heat from it's physical contact with the heads, not from radiated heat. Wrapping the manifold would cause it to retain heat. | ||
| Lornce |
Hootowl, Be interesting to know if that were the case while sitting in traffic on a hot day or while flying down the highway with the engine radiating huge amounts of heat energy but with lots of cooling charge passing through the intake manifold. I'm guessing the two scenarios may be quite different.... Anyone know, have data? Care to speculate???? Lornce | ||
| Joey |
Hey, Rick! I just read a link you provided. Here's a quote that got my attention: "Its a controlled froth. I won't kid you, it's very difficult to control. Its much easier to build a carburetor that operates on a vacuum to ratio concept. But the fogging advantage is gone." It seems they neglected to mention that feedback carburetors actually do an excellent job of keeping the fuel/air mixture accurate. About the vacuum to ratio concept: That's how the Fish carburetor works. It is much easier to build, since it is incredibly simple. That would explain why a relatively small vacuum leak below the carburetor makes the Fish carburetor work remarkably poorly, whereas a conventional carburetor would only be somewhat affected. (Been there, done that.) Making the throttle plate the location of the venturi by putting the holes in the throttle shaft fixes the loss of the fogging advantage as far as I can tell. Hey Blake! Thanks for giving me these free lessons! Although I managed to learn a lot of that stuff on my own, it sure helps to have it all put together in such a way that gaps are filled in and such. I think I'm understanding more why the Fish carburetor works. Rick's link above, from which I quoted, put something into perspective that I hadn't realised. Correct me if I'm wrong, or if I'm not quite understanding: In the Fish carburetor, since the fuel is introduced immediately under the throttle plate, at the highest point of turbulence, and at manifold pressures, rather than at ambient pressures such as with standard carburetors, would that not result in more efficient vaporization? It seems that the presence of hydrocarbons (unburnt fuel) in the exhaust would show evidence that the fuel droplets that are introduced into the engine are not as well vaporized as they could be during idnition. Therefore, if the fuel was to be mixed the way the Fish carburetor does it, would that explain the increase of efficiency of the engine that has this carburetor mounted on it? Also, that would seem to logically explain why the Fish carburetor, while at WOT, has no significant advantage over a standard carburetor at WOT, don't you think? It seems that, according to Rick's link, EFI's advantage is the well-regulated fuel/air ratio. I know the Fish works. If the stock carburetor was so far out of tune that I could make the differences I made without the Fish being significantly more efficient, wouldn't there be some noticable signs, such as hard starting, and perhaps clouds of black smoke trailing behind? I bet a good English major could get everything Rick said and make it seem like he was arguing with himself, but that's irrelevant, so I won't even mention it. Oops! Looks like I already did. Sorry, Rick. | ||
| Reepicheep |
Lornce... I was thinking a similar thing, but instead of wrapping the intake, I was thinking run a metal fuel line around against heads for a few loops. Cool air means more power, but warmer gas means better vaporization. As Blake just taught me on this thread, the pressure drop causes vaporization *before* the drop can adjust to the cooler temperature of the intake air. So what if we just warm the fuel before it hits the carb, but leave the air nice and cool? My thoughts? It's too simple and too obvious, which suggests to me that a) it was thought of already and b) it was not done because even without it fuel is ALREADY is sufficiently vaporized for good combustion even with the standard setup. Which neatly brings our tangents full circle Bill | ||
| Lornce |
Ak-chooly Reep.... Don't be too quick to discount the notion. While absorbing radiant heat to preheat the fuel, you'd also be masking heat from the surrounding parts ie: intake manifold. However, the heat radiated would be far in excess of what's required to pre-heat the required amount of fuel.... Also, I'm guessing there may be a limit to the amount of fuel that needs to be pre-vapourised prior to combustion for peak efficiency???? That's sorta' what I was getting at with my question re. how well my S1 ran yesterday at -8c... The supercold intake air must have had an effect on the vapourization of the fuel in the charge.... and subsequent power produced? Or maybe the cold dense air just revealed a 'too rich' jetting situation.... Hafta give the plugs a look.... As I recall my old '81 Celica had a coolant line and jacket to preheat the carb and fuel. Lots of other vehicles had/have similar systems too, so yours is not a moot point. Modern bikes with forward gathered air induction plumbing also facilitate cooler/denser intake charge.... So there's two practical approaches to the problem already. I'm certain there's dozens more.... I need a motorcycle ride, Lornce | ||
| Hootowl |
Reep, If warm fuel makes more power, why do drag racers coil up their fuel lines in a buckets of ice? Lornce, I doubt very much that the manifold (once at operating temperature) would ever become cooler than the surrounding air. If that is indeed the case, it will radiate heat, not absorb it. | ||
| Davegess |
WOW, I'm gonna keep my head down. Somebody is gonna get hurt with all this ... getting tossed back and forth. Great fun. | ||
| Reepicheep |
Hoot... Interesting! I didn't mean to say warm fuel makes more power, I meant to say only that warm fuel would in theory vaporize better... I actually suspect the there is no difference, and that it already vaporizes fine (due to the decreased pressure) for proper combustion at ambient temperatures... though Lornce has some interesting data points. I recall cold air gives more power (over rich jetting issues aside), though I forget the theory behind it (I think there is more to it then air density). I can feel it on my M2. The only time I get 2nd gear throttle only mini wheelies (the only wheelies I do, the 8 inches of front wheel off the ground during accels) is when it is 50 degrees or colder out. I wonder why the drag racers ice down the fuel? I have heard of icing down the manifold, which makes good sense for a drag race where tenths of a seconds matter and you have lots of prep time for a single run. But I can't think how the cold fuel would help, unless there is some special rules loophole (can't ice the manifold, but can ice the fuel) or some special characteristic of the race gas and high performance engines (detonation, etc). Cool discussion! | ||
| Rick_A |
Reepicheep....That's the whole of the misunderstanding here...my knowledge on the subject is based on the idea that a "vacuum" is not created...that it is a pressure difference...the same way of saying the same thing. The whole basis is that it is atmospheric pressure that fills the cylinder. I have danced around no issues here. Apparently, the science community and technical publications like to call that a vacuum as well, as Blake has asserted...but for all intents and purposes, it obviously confuses the issue...does it not? Warm fuel doesn't necessarily make more power. A cooler intake charge will. That's why drag racers cool the fuel. That's why vaporization devices bring little to the table. When an engine is at operating temperature, as long as the mixture is atomized, it will vaporize and will burn with the heat created by compression. Which should have triggered a little light-bulb somewhere to make you think... "wow. If there is that much vacuum to make that much flow, I wonder what a mist of a volatile fluid at medium to high temperatures and such low pressures will do?". And then from there it would not have been far to get to "Wow... what is the vapor pressure of gasoline, and how long can it exist in an atomized (mist) form under a vacuum significant enough to flow around 136 liters of air in a second?" There lies more misgivings...it has already been established that the air/fuel charge cools...it is not at "such low pressures"...the actual pressure drop from atmospheric is typically a fraction of a psi. The movement of the piston creates the flow of atmospheric through a pressure differential. It is still atmospheric pressure that "pushes" in. Another factor is the length of time that the mixture has to reach the combustion chamber...not long...that's another factor affecting how much vaporization can occur despite the factors present. Answer me this then...if the pressure drop is so significant then how can near 100% volumetric efficiency be possible with a normally aspirated engine? The manifold can be hot...that doesn't mean the air/fuel within is going to be significantly heated...or vice versa. | ||
| Rick_A |
Whatever way you want to describe it, however you want to look at it...all I had asked from the start is that Blake prove his assertions...and despite all this rambling that has not in any way happened. Everything I've read about the subject leads me to believe that while vaporization does occur...that it is apparently not to a significant degree. Blake, you have yet to conclusively prove otherwise. | ||
| Hootowl |
"Answer me this then...if the pressure drop is so significant then how can near 100% volumetric efficiency be possible with a normally aspirated engine?" Rick, Exhaust scavenging, and the momentum of the air in the intake tract can fill the cylinder beyond what would be expected at a given pressure. Tuned port intake runners use this method to improve volumetric efficiency. When the piston reaches BDC, the fresh air doesn't stop moving in. It has mass and velocity,or inertia. On the exhaust side, the inertia of the gases flowing out of the headers helps to pull in the fresh charge. This is why an exhaust overlap helps build power at hight RPM's. Which is why it is possible to achieve, (some say exceed) 100% volumetric efficiency. Jeff |
