| Author | Message | ||
     Sarodude |
X1glider- I'd really appreciate it if you could recommend to us some good books covering wave theory and fluid dynamics relevant to IC engines. I think a lot of us have SOME idea of what's going on without a full concrete picture. Some advice from a fluid dynamicist would be cool... -Saro | ||
| X1glider |
1st off, we might have our definitions mixed up. You probably mean to say momentum, kinetic energy or kinematic energy and not inertia. The definition of inertia is the property of matter which causes it to resist any change of motion or it's state of rest. This could be something as simple as a fuel molecule's mass, since in liquid form it is heavier than air and takes more force to get it moving. That said, in a fuel injected bike, since the fuel is being sprayed out by an injector under high pressure, intake close can be earlier than on a carb model and our topic of discussion won't play much of a role. This is the beauty of having 4 cams. Mix and match, baby!!!  On a carb model, fuel is constantly spraying (instead of injector pulses) into the intake tract and needs the velocity of intake air to bring it up to speed. So intake closure can occur later. The way a cylinder fills up has much to do with why the intake valve closes so far ABDC. Sometime BTDC. Intake opens (exhaust slightly open still), air is pulled in toward the exhaust side of the cylinder. 0 TDC. Sometime ATDC. Exhaust closed now. Air is sucked down the wall of the exhaust side of the cylinder. Piston at 0 BDC. Momemtum of air runs into a dead end, so it starts to travel across the piston face. Piston starts upward (ABDC). The air is still flowing into the cylinder, so it forces the air already in the cylinder to travel up the intake side of the cylinder wall. Intake valve closes. Cylinder fill complete. I concur on your final points too Aaron, which is why I won't put my HOG over 9.5:1 compression ratio. I laugh at the wanna be cool fools with the REALLY BIG inch high compression engines. Yeah, backfiring and stuttering is what a well tuned engine sounds like!!!  BTW, if you have the full specs on the stock cams for my X1 including wether the lobes are symmetical or asymetrical, I'd like to see them so I have a starting point for my future mod plans. | ||
| X1glider |
Any books I'm familiar with only apply to pump design which includes impellers, diffusers and volutes, nothing which have pistons. And the intent in my profession is to create velocity and not pressure. Sorry Sarodude.  | ||
| Aaron |
Well, inertia is the term used in all the books I've been able to find on the subject. Whatever. X1 cams are .497 & .497, 28/48 & 52/24, .211/.191 on the tdc lift | ||
| Blake |
Saro: The Internal-Combustion Engine in Theory and Practice (Volume 1: Thermodynamics, Fluid Flow, Performance) Second Edition, MIT Press Charles Fayette Taylor This is for the reader with a technical background in basic fluids and thermodynamics. I wouldn't recommend it for the average layman. | ||
| X1glider |
Mucho gracias on the cam specs. I didn't realize it was a std screaming eagle cam. I was guessing Buell had their own design. I know, wrong section of the board. | ||
| Blake |
I think the term "momentum" acurately describes the combination of inertia and velocity that we seek to optimize in our intake and exhaust tracts? X1G: If what you say were true, "On a carb model, fuel is constantly spraying (instead of injector pulses) into the intake tract and needs the velocity of intake air to bring it up to speed. So intake closure can occur later." the cam/valve timing of a DDFI engine would be different from that of a carbureted engine. As far as I know, they are identical. The airflow in a carb system is far from constant. The carburetor delivered fuel pulses in time with the fluctuating airflow. Not totally dissimilar to the delivery mimicked by an injector system. | ||
| X1glider |
As copied from previous post: The definition of inertia is the property of matter which causes it to RESIST any change of motion. Perhaps this matter is sticky by nature, like glue, therefore offering resistance. Momemtum=mass*velocity, therefore inertia doesn't apply since the object is already in motion. Anyway, I'm tired of physics now. If Buell wanted to do it totally right, they would put in different cams for FI and carb models. Even the harley big twins have different cams for carb and FI. Goto \newurl http://www.andrews-products.com/cams/products/twin88_fr.htm Both stock ones are printed for comparison. My hog uses a CV instead of flat slide, mainly because I like to tour from sea level to 7k+ altitude, and it does quite well at compensating for air pressure differences, wether it is altitude related or if the barometer should simply rise or fall. Here, Blake, is where the airflow being constant come's in. The goal of the CV is to keep the MAP and velocity constant for a GIVEN (unchanging) load (throttle position) regardless of variations in barometric pressure or altitude. Naturally if you twist the throttle the velocity will change. The key is an unchanging throttle position in the CV equation. Doing this, the CV allows the cylinder to fill up only as required for a given load, not necessarily 100% fill. Perhaps, if you are going 55 mph in 5th gear, only 40% fill is required to hold you there. The CV carb isn't perfect, but it tries. On a flatslide, if you held the throttle constant, and the barometer dropped suddenly, the velocity would change. I guess you're correct on the fuel PULSES in a carb, since the intake is shared between cylinders. The constant stream of fuel is broken up into pulses from being pulled from front to back to front to back, etc. So I am wrong about a steady stream of fuel bit. | ||
| Loki |
Did I start something bad here? Hope not, cause I am learning something. Besides I chase roaming and lost electrons for a living. | ||
| Aaron |
X1G said: "You can get over 100% cylinder fill, but that requires turbos and superchargers. " Do you really believe this? It flies in the face of every engine theory book I've ever read. There are several effects that, if exploited properly, allow a normally aspirated motor to exceed 100% VE. | ||
| Ara |
Oh boy, Aaron! You have opened Pandora's box! How exactly could that be accomplished on a non-FI Buell??? Russ | ||
| Aaron |
Wave travel in both the intake and exhaust. We've discussed that to death in other areas of this site. Exhaust augmented intake flow. Another thing we've discussed. The "momentum" of the intake charge (still think the word "inertia" makes sense). Effective ram-air setups. FYI ... Denish speaks of VE's as high as 130% in normally aspirated Harleys. Bet it's higher in some Japanese bikes. | ||
| Blake |
 Inertia certainly does apply. If air is moving inside an enclosed pathway, like an intake tract, its "inertia" tends to keep it moving even after the intake valve closes. The air within the intake tract continues to move forward and builds pressure. If the next opening of the intake valve occurs as the pressure builds to near a peak, the inertia of the air has been utilized to an optimumally to improve cylinder fill. As we know, the length and cross sectional area of the intake tract can be optimized to take advantage of the air's inertial effects for certain rpm ranges; this is simply exploiting, among other things, the momentum or inertial characteristics of the air within the intake tract. When speaking about linear motion of gaseous fluids, the concepts of inertia and mass are pretty much interchangeable since the ONLY variable affecting inertia in that respect is... mass.  This is no different for the case of linear motion of solids. We simply use "mass" in place of inertia. Only when rotational motion (rolling, pitching, yawing) enters the picture do we need to begin worrying about the mass moments of inertia for the particular axes of rotation in play. So, Aaron is perfectly correct in using the term "inertia" as was I in using the term "momentum" to describe pertinent attributes of transient gaseous fluid flow. | ||
| X1glider |
Wow! I'm amazed at all the attention this topic is getting. At least someone is paying attention in here!  Well, I won't argue terminology with everyone, we'd need a new section on this board. For anyone interested, get some real physics books. Boring reading tho. I am interested in the book Blake suggested. MIT press? Must be good. An engineer I work with came from there and knew someone in the early 80's who had a grant from HD to do his thesis on exhausts for their flat track bikes. I'm just a lowly fluid dynamics engineer who also worked on diesels at one time and therefore mixes my knowledge of both to fuel my fun. Obviously the fact that I design axial flow pumps and do CFD for a living doesn't make me an engine engineer, but it does give me a unique understanding of how and why an engine works. I'll have do a CFD study on an engine model one day. (mental note) It's cool tho that we seem to all be on the same page for the most part regardless of a few differences of opinions. Guess we're all set in our ways.  | ||
| X1glider |
Aaron, I haven't read these engine theory books you speak of, but I have a very hard time believing you can get 100%VE from a normally aspirated engine. You must enlighten me and tell me where you found this info so I can see it for myself. I used blowers as an example because most of my diesel experience involved engines with tri-lobular blowers (superchargers) on top. VE on these was claimed by Detroit Diesel to be 400% at idle (550 rpm). | ||
| Rempss |
X1, Author - William Denish. I have 3 books by him V-Twin Tuner 1 & 2 and the Big Twin book. He may have others, but these are very complete and easy to read/understand. Jeff | ||
| Axtell |
Blake, I set here with my well worn copy of "the internal-combustion engine in theory and practice" with a smile on my face. Ya know, there isn't a hell of a lot of new info around since old Harry Ricardo did his work. Big change might be the metal alloy technologies and this new- fangled computer power,Ron | ||
| Blake |
Ron: Heheh... Yeah, we don't need to worry about burning up exhaust valves so much any more do we? And as to the computer power. More often than not, canned computational analysis programs tend to make the ignorant appear wise. Easy to use analysis programs often instill a dangerous false confidence in inexperienced engineers. I'm sure X1Glider will agree that even CFD (computational fluid dynamics) can be VERY dangerous when used by the untrained/inexperienced. Got any other books you would suggest for us amatuers? Thanks for poking your head in here every once in a while. We sure do value your input. | ||
| X1glider |
Yep, there are quite a few out there who like the pretty pictures FEA and CFD produce. I like em too.  But, I can actually make use of their output to improve my designs. So, please, no bashing. I know my capabilities, no one else here does. I'd like to think I learned something while achieving my masters at Cal Tech and on a day to day basis. I'm simply here to help if I can and to be helped as well. And thanks to those who are helping! As for for books, 2 I keep for reference are: Fluid Mechanics with Engineering Applications by Robert L. Daugherty. McGraw-Hill Book Co. (He's a Cal Techer too) Applied Fluid Mechanics by Robert L. Mott. Charles Merrill Pub. Co. Fairly rudimentary books and have very little that could actually apply to engine design. But the principals behind the design process are all the same. Geared toward the pump industry mostly, but with a little creativity, can be made to apply. Only problem with all this knowledge is that one can come up with the ideal design on paper, but when the pattern maker, foundry and machinist come into play, the end result is not the same. At least that's how it is where I work. I work for Hydrotex not NASA! | ||
| Blake |
X1G: No bashing here amigo. I assumed you were one of the good guys. | ||
| B2m2 |
This is my first posting so please try not to scrutinize it too much. I had the opportunity to put my M2 on a dyno this past weekend and found a few extra HP I didn’t know I had. By removing the nylon rain cover (Dry Charger filter wrap) off the Force Winder air cleaner the bike gained 3.5 HP over the first dyno run with the cover on, of course this was spread out over the last 1,000 rpm. I like the looks of the cover over the bare air cleaner element but, I like the extra HP even better. I hope you can use this info. | ||
| X1glider |
The dry sock is most likely made of a "breathable" material (similar to Gore-tex) that lets vapor thru but keeps liquid size particles out. The small micron pass thru restricts the air flow to some degree as well as the rain to a larger degree. You saw the difference in the high RPM range because that is where Buell's are designed to breathe, high flow rates at high rpms. Just keep the sock under the seat until needed. Who's gonna see it anyway when you're blowing by them? | ||
| Blake |
Good info! Can you post the comparative dyno plots? | ||
| Roadrunr |
hey b2m2;throw away the dirty sock and keep the 3 hp on the ground where it belongs.  Keep tweakin and one day yer m2 might grow up and be an MX1   | ||
| B2m2 |
Blake, I wasn't given an e-copy of the dyno plot. I guess there's a lesson learned here, I'll ask for one next time. Roadrunner, Most people own bikes that they can't ride to their full potential, I'd rather own one that I can. See ya in the rear view mirror. | ||
| Reepicheep |
Aaron... you are awfull quiet here. Any opinion? On one hand, I could understand why removing the sock would bump up top end, but on the other hand, 3-5 hp sounds like it could easily be normal run to run variation and not statisitically significant. Sounds like something to test next time you are bored on the dyno. | ||
| Sarodude |
It's interesting that Ron mentions the Ricardo book. Another very respected engine authority (in the VW world) by the name of Bob Hoover constantly refers to Ricardo. Interesting... -Saro | ||
| Aaron |
No, can't really comment on the dry sock thing, since I haven't done that test. 3-5 is a little much for normal run to run variation, though, assuming the bike was fully warmed up. Day to day maybe, if conditions are radically different. Be interesting to see an a/f chart with & without the dry sock. When I get a chance. | ||
| B2m2 |
Gentleman, just to keep things straight here, I tried to post 3 (point) 5, not 3 (to) 5 HP. Just trying to keep things on the up and up. | ||
| Reepicheep |
Sorry for introducing the confusion... I appreciate you posting the information... I just got back from a ride on the cyclone, and did a simple test. At WOT, the rain sock does indeed get "sucked" against the filter, so there is some non trivial restriction. I just threw the "Aaron Bait" out there because I have yet to find a dyno tuner around here... all my tuning has to be second hand |
