De-atomization of air fuel mixture in intake tract of IC racing engines PART 3 of 3

so at the convergence point what will happen is if everything isn't designed properly when the flow velocity moves up and makes the short side reactive what you're going to see is the port becomes turbulent it gets loud and anytime a port gets loud you know there's something wrong i mean i can hear a good port or a bad port from across the shop i mean after 36 years of doing this audibly anyone that's been in this game long enough um can hear an engine's power band something wrong with the engine from across the shop or the flow bench too there's certain sounds or tones i should say that a port will make when everything is tuned properly it's very smooth you shouldn't have the port get loud so if it goes turbulent and gets loud at 600 between 550 and 675 lift you pretty much know that something's out of whack the venturi here is out not shaped properly the short side's too forward something is going on so what happens here is when this port hits that convergence point the flow switches sides so here at low lifts it's spinning this way once it hits a convergence point it switch sides and start swirling this way so when this happens power goes down because you have fuel droppers running in each other de-atomizing and it's kind of a mess you can mitigate it somewhat with smaller throats and bigger back angles on the valve but you really can't ever fix it unless you change the overall design or architecture of the cylinder head so this is what it looks like in the port of course it had a radius on here so all the fuel at low lifts was here on the push rod side and then higher lifts past the convergence point it moved over to the straight wool side this is what it should look like no matter what the lift is the flow is always on the same side of the port and this port has been filled in here and moved its location in order to achieve that you notice here the low lift flow is on this picture is red and the high lift is blue you can see it coming out and looking there with daikum we can see where that vortex generation is if you flow enough dikem in here you'll be able to see the vortex generation on the other side and going back to the flow bench some people have asked me well does it matter do you want to hit the exact air fuel ratio on the wet flow bench that you do on the running engine the answer is no um you can have a anywhere from a 20 to 1 air fuel mixture down to a 5 to 1 air fuel mixture and all you're going to see is these vortex generations get larger or smaller so that's unimportant okay backing up here okay now i'm going to touch a little bit on turning the fuel the short side of course is the lowest localized velocity highest pressure drop and localized velocity there's in the system and we try and turn that in here turn that's what turns the fuel this is the highest pressure drop fastest average velocity in the system i want you to notice how that combustion chamber comes out it comes off that radius and it's not laid way back it recovers that pressure on both sides as equally as it possibly can and this is the cfd of the velocity gray velocity being higher green being lower this is a short side that's been this is a short side that's been laid back too far the bend is more gradual this is actually a more abrupt bin it lowers the pressure here so in the grand scheme of things you would think oh well i could lay that short side back i get a better line of sight but you can't turn the fuel and on the wet flow bench what you will see is the vortex generations if you have the short slide messed up and it can't turn the fuel those vortexes will grow in size instantly and usually the chamber the way everything's designed the valve location and the chamber lay back and everything like that you're not going to affect where those vortex generations occur unless you can change the architecture of the cylinder head meaning raise the port and move it over rotate the valves in the combustion chamber then you can move those vortexes relative to the location of the spark plug and the valves but where they are located in the combustion chamber cannot be changed unless you make a big change in the design overall design so this is what happens when you try to bend the runner and make air go around a corner when you don't want to so this is the flow direction and as you see all the air comes up here and it tries to conform to this surface but it breaks the boundary layer narrows up the flow field and this is air that's actually going this way it's literally trying to go back up the pipe it sits here and does this number so that just shuts the flows on them and this is why we don't bend runners we try to make them as straight as possible all the air comes up rams into the top and narrows that flow field way down so the flow path through any pipe is a straight line it goes from here to here to here so the more you bend that pipe the more velocity gradient you build at the apex of that bend the deader the roof is the more active the floor is and if you bend it too much in some of the older manifolds all the fuel will just lay if the fuel is coming in this way what will happen is this pressure drop will try to pull it around the corner it'll try to grab the airflow coming down will pull that fuel down but it can't do it so it rams all into that back wall and de-atomizes and this again is that vortex generation so it keeps the fuel on this side you can't make a turn so you want that runner as straight as you can navigate one turn and then it's over you can always navigate that one turn but trying to navigate a nice gradual turn which looks aerodynamic and it looks like the right thing to do but in actuality in the running engine it's actually severely detrimental so as the air tries to come around the corner the boundary layer condition here this being the fastest air speed it tries to make that boundary layer and it tries to pull that fuel but what happens is the top air speed gets ahead it starts moving ahead and then as soon as it breaks the boundary layer here the air tries to go the opposite direction and you get turbulent flow what pulls air around a corner the pressure drop and atmospheric pressure is what pulls the air in the corner it's called the coanda effect a short side works off a condo effect a wing design coanda effect comes into play when you're designing the wing of an airplane i'll touch on that a little bit so what what's happening here the koando effect is high velocity air hits here so the higher this velocity is the thinner that boundary layer gets so the thinner that boundary gets so the lower that pressure gets atmospheric pressure pushes in on it as the velocity increases the pressure drops when the pressure drops the atmospheric pressure pushes in on it so it wants to adhere to that surface and it will adhere to that surface as long as the velocity has that boundary layer thin as soon as it can't adhere to the surface it breaks that boundary layer it will go turbulent this is a little apparatus that shows the cowanda effect what it is is just a pipe with a rounded nose and here's a pressurized plenum that shoots a jet of air out here and if you guys want to see the coanda effect you can actually see it just take an air hose an air and shoot it off the edge of a table and the air will hit the edge of the table and actually turn you can use smoke or whatever and you can actually see the colander effect in action and even off of a sharp edge it will try to turn it but on a radius it lowers that pressure so atmospheric pressure is pushing in on this so as long as it can maintain a high airspeed it will conform to that surface as soon as that air speed drops it can no longer maintain it adhere it can't adhere to the surface the bow driller gets wide it breaks and it goes turbulent and this is how air goes around a short side radius not a wing if you notice if you lower the flaps on a wing it has to come around here and by the way you know we're always taught in school that you know developing a wing the cord of the wing the air goes faster over the top than it does underneath it's called the bernoulli principle that's wrong actually only 10 percent we were taught wrong in school and i have talked to aerodynamicists at boeing and i have watched some educational videos on this and it's simply amazing that only in the last 20 years have they really understood how a wing creates lift and it's deflection deflection is how a wing creates lift it aims the air down and it pushes against the air at the base so the air the stagnant air has inertia so it's pushing off the inertia of the air below it so i'm right here you're looking at if you look on if you're ever on a 747 and you look out on the wing right at landing they lower the flaps and on some of them they have a cord on the front that comes out what this does is if the flap is too low the velocity drops and the boundary layer gets too wide and it goes turbulent or stalls the wing so at a high angle of attack you've got all the air coming out and it can't create low pressure here or the pressure is not low enough here to let the air adhere the boundary layer gets big and it'll break so what they do is you'll notice that when they lower those flaps there's big there's spaces underneath there the reason they do that is to grab high velocity air right here to accentuate that koanda effect and force that air to adhere to that huge flap hanging way down there which gives them more lift so you know we're taught in school that you know the air takes a longer path here so if it takes a longer path here it has to speed up if air speeds up the pressure drops and here it takes a shorter path and the bernoulli principle states that equal transit time in other words the air here and here takes the same amount of time but what they found out that that's not exactly true the actual attitude of the wing is and deflection of the air is actually what creates lift when ninety percent lift the quad or the bernoulli effect is only responsible for about eight percent of the total lift on a wing now if the bernoulli principle was actually responsible for all the lift of the wing a laminar flowing wouldn't work a p-51 mustang wouldn't even fly and we all know that's not the case so laminar flow laminar flow means that the air all the air the lines of the air are conforming to the surface in a string straight lines so here you see that the velocity is equal on both sides of a laminar flow wing so this one on the one design basically off the bernoulli principle the boundary layer will grow the velocity drops and you get turbulent flow off a major portion of the wing but a laminar flowing the velocity is high enough to lower the pressure to where the boundary layer will whether here for a longer distance which reduces or increases the efficiency of the wing now we're going to look at wings and ports why i put wings in ports and what the actual flow path is through a port now again the short side the kolanda effect we lower the pressure here and usually the short side air speed will range in a properly designed port anywhere from 320 to 380 feet per second rarely will you ever exceed the test pressure on the bench on a localized velocity in other words if you're if you're flowing at 28 inches 28 inches is 350 feet per second so if you exceed 350 feet per second at the apex of the short turn you're playing with fire you can at that point you get in into you know it'll go turbulent at higher lifts or it could go toward higher lifts in some cases though you have to do that everything has its place there are engine designs that work at lower rpms uh low engine speeds that have to have what we call hypercritical short turns that are up in the 300 and even 400 feet per second range but that's a that's not an unlimited racing engine that's not a racing that's something that has to operate from 1500 to 3000 rpm now i've always said you need a nice line of sight all these angles come in and converge to the seat which is the fastest average airspeed this is the highest localized air speed being the apex of the short turn but air wants to go in a straight line it does not want to make a turn and anytime you instigate a turn that's a flow loss or loss in energy it's less air you're going to get in the combustion chamber but again this goes back to i'd rather make one turn than have this whole thing arced all the way to the valve that's not the proper way to do it so you see these flow lines coming in and they're basically they're trying to go as straight as they can and on a properly designed port the velocity gradient here and here will be equal so what i mean by that is if you measure the air speed here it'll be 300 here on this wall it'll be 300 and 340 over here and 295 on the base on the on the floor if you have a port that's really low which i'll show you here in a minute every time you lower that port it's going to increase velocity gradient so i'll explain why that's detrimental we notice here at the short side that the flow lines converge to the middle on any port the fuel trailing on that floor will converge to the center of the short side and that is why we use a wing and i'll show you that here in a minute too now you notice that this is an extremely low port kind of indicative of a 23 degree small black chevy the flow lines still want to go straight and the apex being the short term they want to turn here but it has to navigate these directional changes it doesn't matter how much you kick the walls or lower the floor but a certain point no air is going to flow down there what you've done here is instill a large velocity gradient up here you're going to have 340 feet per second and down here you're going to have 180. here you're going to have 350 to 380 feet per second and up here you're going to be lucky to hit 200 feet per second why is this detrimental because anywhere those flow lines aren't attached to that surface fuel falls out this is de-atomization areas right here so the fuel comes in it can't make the turn so it smacks on the back wall de-atomizes and when you de-atomize the mixture of course you're going to increase the vortex generations and you're not going to get usable power out of that fuel and a subsequent really bad thing about that is when you generate fuel vortex and you have that falling out of suspension that's fuel that's de-atomized from the air now let's say you tune a perfect air fuel ratio to that thing well if you're pulling fuel out of the air you're leaning the mixture up so you're going your lean areas in the combustion chamber are going to get really lean at that point so that makes the combustion chamber detonation sensitivity sensitive anytime your fuel falls out of suspension that detonation sensitivity that combustion chamber rises and there's nothing you can do about it but try and handle the fuel try to re-atomize the fuel and there are certain things you can do downstream here to do that to help that out that situation out also we've on these low ports because we've got to go around a push rod we kick this out to get enough area here to navigate the turn around the short side radius well again the flow's going to want to go in a straight line so it doesn't matter how much you kick that out that air is not going to go over there so now we've instilled the velocity gradient across the short side radius itself not just upstream here but also at the short side itself so over here you'll see 380 350 340 and over here you'll see 200 feet per second if you're lucky but this is a necessary evil imports like this we we have to make this area bigger than it would have otherwise been necessary because of all the directional changes this thing has to make so this is something we have to put up with in these ports you notice also the fuel and airlines converge to the center and i'm going to show you some poor man's wet flow here in a second so in a lot of my ports you will see not all of them but just in cases where it's actually functional you'll see me put a wing on the floor and that wing does not protrude past the apex or past that wall right there you're not going to send that wing out into the bowl it's usually just a continuation of the floor and it follows that back the back wall or lay back of the short turn and what that does is it makes the flow line separate which also separates that fuel because if you don't have that there all the fuel goes to that center and it forms this nasty stream de-atomized this is a raptor port with the wing in the floor so it's pretty pronounced of course you don't see it kicked out here but you can see what it's doing the fuel's coming in all trailing de-atomized on the fuel that on the floor all that fuel that's falling out of suspension that's just trailing along the floor will be this is a high velocity spike here so what it does is it sends the fuel off to the sides and this high velocity spike will pick the fuel up and spit it back into the air stream it'll re-atomize that fuel and sometimes you'll see four or five horsepower on the average just by doing this now i will say that any port that you do this to any port that you design to have that wing there must be specifically designed for the wing you can't just take a little wing and put it in any port and have it work it it's that's not it won't work you have to be able to manipulate the walls and the air speeds in order to fit that little bit of extra area in there and the air speed spike right there can be kind of critical as well so why do we do that why do i want that well this is past the short term looking from the combustion chamber and you can see that all the fuel has gone to the center of the short side and it's formed this nasty trail of fuel that comes out and what this does is the vortex generation opposite of the sport plug will grow considerably when you have fuel trails like this this just feeds that vortex that's less fuel you can burn to create usable cylinder pressure now i want you to take note of this and look real careful this is the 60 degree cut this is that one definition underneath the seat you see what the fuel did it sheared it sheared and tried to re-atomize that nasty fuel it's trying to do it here but there's so much fuel here that it just can't it can't handle it but this happens all the way around that seat this is a re-atomization vaporization ridge that's why you need sharp angles underneath this seat now what happens when i put a wing in there well again it picks that fuel up spits it back into the airstream over here and splits it and decreases the amount of fuel that's charging that vortex generation opposite the spark plug it reduces that vortex down this is air fuel mixture that is burned to create usable cylinder pressure instead of being wasted creating a bigger vortex burning too late and just going out the exhaust pipe the back cut angles on a valve why do we use back cuts and why why do we use two angles or three angles on the back of a valve well if you think about it you have a 12 degree back angle here and i've got to turn from 12 degrees to like 90 degrees so it goes 12 and this is a 45 degree valve angle i think yeah 45 degrees so you have a 45 degree and you have a 30 degree 15 degrees i think you remember earlier i said you can't turn the area more than 15 degrees at a time so on a 55 degree the steeper valve angles you get you start cutting those angles in increments of 10 degrees so on the back of a valve for like a 55 degree valve angle you have a 55 seat a 45 and a 32 and a half or a 35 so you're cutting it incrementally trying not to exceed that 15 degrees so you notice here that the fuel has vaporized this is a vaporization ridge and this is a vaporization ridge this re-atomizes the fuel it also tunes up the port the venturi section remember the arrow converges to the throat well the air has to get around the valve so what this does is the back angles if you just had a valve with a back angle like this and a seat it's like this but if you put back angles it does this it forms a venturi out that throat so you're tuning that venturi section up and it's not uncommon at all to take a valve out of the box that doesn't have a back cut on it and put a back cut on it and get 10 horsepower on the average it's not a small game i've seen it so many times over the last 30 years very simple thing to do to gain a little bit of power tune that venturi section up with back cuts now i'm going to show you a little wet flow trails this is dykem thrills trails through the port and as you can see the fuel is turning this is the apex of the short turn this is lowering the pressure here and you can actually see the fuel on the wall you can actually see these this fuel turn here at the short center you can also see this wet this this single trail there's no wing in this port at all and this single trail was coming out over the short side here you can see the other side of the port the fuel right at the apex of the short turn it grabs that fuel that low pressure area right there will pull that fuel down and allow it to turn around that corner now let's look at uh dikem trails in the back of the bowl this is the last thing i'll i'll touch on here everybody wants to know where you put the wing behind the guide all you have to do is again hold that dikem out let the port take it in and it'll show you this wing is in the wrong place as you see that the wing should be ended up right here the airflow behind that guide it's telling you where to put the wing this is the this is the easiest way to put that wing exactly to where it'll recover the pressure behind the guide and you won't have any air fuel separation you can see here that it's actually boiling off the side of that if you put those wings in the wrong place you'll actually get air fuel separation past that wing which is not what you want all right this is i think video number three so next videos i'll try to touch on valve seat dynamics and how to tune the proper valve job have a good day you

Channel: Darin Morgan

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Length: 27min 1sec (1621 seconds)

Published: Wed Feb 24 2021