HiFlite999

iTrader: (2)

I really think it would help if the word "vacuum" were completely eliminated from automotive vocabulary. Physically speaking, there is no such thing as a "vacuum leak". What's leaking is air, it's an air leak, period. Rather the same idea as the dummkopf tv people who say 40 deg F is double of 20 deg F, or if you prefer 20 deg C is twice as hot as 10 deg C. 20 deg C is 3.5% hotter than 10 deg C, referenced to a true zero.

Flow (aka horsepower) is related to pressure (aka boost) in the same way your commute time is related to the day of the week. By taking data over some period of time, you can reliably predict your route is faster on Sunday than Friday. That doesn't mean there is a fundamental physical connection between the two, even though you can relate them, chart them, and even use them to make predictions. From these charts you could also with reasonable certainty conclude that your engine produces on average more power on weekends vs. weekdays (mine does anyway.)

Again, suppose you have a super-new, electrically-powered super/turbo-charger, you close off any popoff valves, and you chart pressure vs. horsepower. The maximum boost will happen with the engine switched off, and will be only slightly less with the engine idling. Not only is boost not related directly to flow, it is not even directly related to power.

Yes, like the airplane drivers, for a given engine, you can chart out a Tuesday/Sunday relationship between manifold pressure, as measured by a simple gauge, and dyno power output. Once you have that chart and don't change anything about that engine configuration, you can get a close approximation of engine output, based on mp, rpm, and temperature (density altitude). But pressure is a sideshow, not a main event (such as mass flow).

I'll see if I can find some airplane power charts lying around and put them up as I think it may illustrate a few of these points. Danger Will Robinson: More blah blah ahead!

RIWWP

iTrader: (2)

Your blah blah is quite good though

bose

iTrader: (5)

I also like the blah blah, anything to have this make more sense is more than welcomed.

Brettus

iTrader: (2)

Thankyou
This is all I ever meant to say about the relationship between the two .

MazdaManiac

iTrader: (3)

Dude - you are SO my hero right now.



BUT YOUR PREDICTIONS ARE WRONG!!!!!!!
Its just a correlation based on bad data.
If you flip a coin and get the weather right for a week, are you a genius prognosticator?

You totally turned around what he was saying.
My GOD, you should be a politician.

HiFlite999

iTrader: (2)

Alright, I wrote up a rather long essay on how the engine manufacturer's power charts are used in the process of an example flight. As a 'learning tool', these sorts of airplane engines are useful because so many of the things done electronically in cars are done by hand in an airplane. I'll put up a couple of the charts separately. Please don't complain about the length of the essay; the same subject will consume multiple chapters of a pilot-training text. You are all free not to read it. Discussion regarding any of the technical points is welcome.

HiFlite999

iTrader: (2)

The desired rich (power) or lean (economy) condition is determined by a temperature change relative to the observed peak Exhaust Gas Temperature.

HiFlite999

iTrader: (2)

For a turbocharged version of this engine (TSIO-360), the maximum manifold pressure allowed at full throttle is higher when the engine is warm. Presumably, this takes into account not only the mechanical factors, but that at a fixed pressure and volume, there are more air molecules present at a low temperature vs. a higher temperature.

olddragger

iTrader: (3)

can you factor in water methanol influence?
OD

HiFlite999

iTrader: (2)

This is a massively technically messy subject. Can I? Nope. Has someone? You bet. When I want to understand a tech issue like this, I start by looking back at the history of the first developments in that field. By the time any field has matured for 20 years, the tech papers are so full of jargon, it's very difficult for a non-specialist to sort out what's going on. The peak of internal combustion engine development was around 1945, before the turbine came into its own. Here's one slide from a presentation given in 2005 by a modern expert on this vintage of aircraft engine - www.enginehistory.org.

Essentially, water/meth is an anti-detonation measure that allows one to run higher cylinder pressures (more air/fuel mass) before the onset of destruction as shown on the attached chart. Also it's showing that the fuel/air ratios should also be altered as the water/meth is added to the mix. Notice too that the peak detonation resistance in achieved with the air/fuel mix set around 10, very rich relative to the usually given ideal of ~12. I'm guessing that our Rx-8's tailpipes are sooty is because Mazda is doing the same thing with the air/fuel, running rich to avoid detonation. I hear over-and-over again that water/meth works because it 'cools the intake'. It's very misleading to think of it this way, especially with a FA system. As the "turbo" chart in my above post shows, one can compensate for the "hot" intake charge containing less mass at a given pressure by simply upping the pressure (aka boost). Detonation is not occuring because the intake charge is hot, nor is it occuring because the engine is "diesel-ing". The 'compression ratio' of the turbo itself is only ~1.5:1 at most, compared to the 10:1 of the cylinder itself. A diesel has a cr more like 20:1. Detonation occurs in precisely the same way as what firefighters call 'flash-over': a fire in one location causes infra-red light emission to be intense enough to ignite an ignitable air/gas mixture at another location. In the case of an engine, the 'one location' is the area around the spark plug right after the plug sets fire to the mixture. The radiation from that fire moves at the speed of light, which is much faster than the expanding flame front. The heating from this IR radiation causes the temperature at locations 'distant' from the fire to heat up. If it heats up enough, it catches fire and sends another flame front out, which collides with the first causing a huge spike in localized pressure which can damage the engine. The purpose of rich mixtures and water/meth both is to put something in between the two locations for the IR light waves to 'hit'. That hit causes the energy of the light to be reduced and thus delay the heating of the air/fuel in the 'distant' area. The fact that a diesel has no spark plug is not just a maintenance plus, it's essential to the process. By using compression rather than a spark plug (which always creates an ignition point), the entire charge of air/fuel in the cylinder starts burning simultaneously. Diesel engines cannot detonate (though they can pre-ignite, which is a different process).

In reading airplane engine data and looking at absolute numbers, keep in mind that aircraft fuel octanes are measured differently than in cars. Most 80/87 octane rated plane engines will run fine on car gas, while most 100/130 acft engines will not run safely on even the highest octane street gas. The WW2 and post-war piston airlines used 130/145 fuel that's way beyond what anyone can get their hands on these days. Multi-crew planes also carried a flight engineer who was a busy-beaver monitoring and adjusting engine parameters through different stages of a flight. Even in modern times, race car engines are run with remote telemety and with the help of "flight engineers" back in the pits. All that isn't to say that a tinkerer can do some of these things and see a gain from it, but it is saying that running close to the edge is a really bad idea without a lot of expensive engineering work that's pretty impossible for a handyman to accomplish.

olddragger

iTrader: (3)

Great info to have Hiflite. Appreciate this.
It was especially interesting to see the difference between water and water meth combo.
Presently i dont know of anyone using w/m injection as a factor in tuning the renasis, we are running it for insurance and to guarantee proper octane during high load times?
It does reduce egt's and it does help clean the combustion chamber.
I have a friend that is into planes---you guys are intense
OD

HiFlite999

iTrader: (2)

YW! As a safety feature for turbo'd cars, w/m makes sense. w/m injection by itself however, isn't going to substantially increase power output. That would come only by using up some of that safety margin by running at a higher manifold pressure than what would be allowable without it.

In the wider picture, getting rid of spark plugs would greatly increase the detonation limits. Ford among others is looking into lasers as a means for igniting the a/f mixture. By igniting along a line or multiple lines rather than a single point, the opportunities for 'flashover' (detonation) in the combustion chamber are reduced.

olddragger

iTrader: (3)

yes --i have seen the articles about them--now if they can only get the delivery/cost under control it will be as big of a change as direct ingection (which I really do not like for a rotary engine).
OD

olddragger

iTrader: (3)

just to let yall know---i informed my high school honor student in advanced physic classes about this discussion and asked her to present this discussion to her class. They are studying the properties of gas's.
You never know where you may learn something.
OD

Brettus

iTrader: (2)

/\ don't believe you - pics or she doesn't exist ! Heh

Rote8

Cough, Cough.
What about 40% Nitromethane/60% Methanol injection? (no water)

HiFlite999

iTrader: (2)

Very cool. I hope it's not too confusing. Physics at that level is very idealized. PV=nRT is neat and simple. In most real-world systems though, there's a string of "what about this? and what about that?" which rapidly complicates the situation, moving it from a physics problem to an engineering one, where it eventually becomes simpler to do an instrumented experiment than to solve the mathematics. Physicists are the poets of science, engineers, the conscientious journalists.

MazdaManiac

iTrader: (3)

PLEASE PLEASE PLEASE repeat this every where you can.
Over and over.

The math is useful to explain why something was, not how something will be.

Its like music theory - I was always amused by the folks that thought Bach studied and followed the "rules" of tonal harmony, rather than realizing that the "rules" were derived from looking at what he (and others before him) composed.

Make the music first then figure out why it sounds good.

HiFlite999

iTrader: (2)

So you're saying that if I know 1 liter of water weighs a kilogram, I cannot say that 10 liters will be 10 kg? Nonsense! Where one runs into trouble is in the misapplication of theory or mathematics. Take Newton's F=ma. This means the a=F/m; for any Force and any Mass, you know the acceleration explicitly. In the jargon, it has an analytic solution. In outer space, this suffices nicely. But on messy Earth you got drag, so a=F/m-"Drag". Drag depends on roughly on velocity squared which is then a function of acceleration*time and involved a 'constant' which isn't constant. That 'constant' depends on the density and flow characteristics of the medium through which our mass is moving and the shape of the mass, the Reynold's number, and so on. The equations quickly become non-analytic, in other words, impossible to find and exact solution for. But, if the mathematics are set up properly (which can be fiendishly difficult to do), a computational solution always exists. This is the kind of stuff that a Boeing can pull off, designing an entire airliner in computers without building a whole series of prototypes in advance. They know to a high degree of accuracy what it will fly like before it's ever flown. Increasingly, car makers do the same thing, for example 'crashing' thousands of computer cars, before making a single real one. Are there glitches and surprises? Sure. Each time there is one, ideally the computer model is improved until its predictive ability can be relied upon.

Again, not at all, otherwise music would be a branch of science. Plus, all science relies on the work of what others have done before (which doesn't make it any less a science). Still, within limits, science can be applied usefully to the service of music. Every major modern concert hall is designed with significant input from those specializing in acoustics for example. Bach himself was a scientist of sorts, coming up with an 'equal-tempered' tuning scheme that allowed changes of key signature during a piece for 'fixed-pitch' instruments like the organ or guitar. (An un-fretted instrument like the violin can adjust pitch on-the-fly.) Still, music is highly experiential. You will not understand Bach's genius until you hear it, and not fully understand it until you hear an organ work played in a similar to original venue (cathedrals) where the the hall's shape and its stone walls introduce a peculiar echo, an echo which becomes part of the music which you are hearing 'live'. You are not only hearing what is being played now, but what was being played a couple of seconds ago and the echo, quite intentionally on his part, fits in. Amazing.

MazdaManiac

iTrader: (3)

But, they know this now by having decades of hands-on experience with crashing real planes with real pilots and the ability to "fudge" the engineer's math so that it aligns with the reality.
The next time they used the "fudged" math, the outcome was more predictable and the "fudged" formula became the "real" formula.


To extend that metaphor to my original point - Bach didn't have access to that math. He had a practical experience with the acoustics of the Thomaskirche and lived with it. But his written notes work perfectly everywhere, all the time.
The math for the acoustics was approached over the intervening centuries, but the "theory" about his harmony decisions was totally derived from his music, not the other way around.
The math that explained (to some extent) his harmonic choices might have existed "in the wild" before he wrote BWV 542, but he was only aware of it through his own ears and consciousness.
By the time you get to BWV 1080, you realize that acoustics had little to nothing to do with Bach's choices. Those notes existed in a space that only exists in the mind.

(BTW - Bach didn't invent equal-temperament. He was just the first composer to fully exploit well-temperament [which is not quite the same thing] in a demonstrative fashion.)

olddragger

iTrader: (3)

I do belive you both have just put to words why I like turn the radio off and listen to this engine during driving!
Please continue these discussions as I am a devoted believer in both science and art (for lack of a better word) and enjoy the dialog.
OD

zoom44

the guy had charlie manson living in his house

MazdaManiac

iTrader: (3)

Well, technically, Wilson created single-part vertical harmonization, which is not really like true, muli-part polyphony.

A true 6-part harmony would consist of 6, independent melodic lines that integrate horizontally - this is precisely what Bach did.

Composing single-part harmonization is an art and a technique that every composer sets his mind to at some point. All the great arrangers of the jazz era did this as a daily exercise. Listen to the horn parts in a Sinatra record.
But, composing polyphony on the level of that which Bach was engaged is something that hasn't been really practiced by more than a handful of composers in history. (And Bach could do it on the fly, which is a bit akin to writing a sonnet on the head of an arrow as it is passing by your head.)

Wilson was the S-AFC to Bach's Motec.

Brettus

iTrader: (2)

So in the context of the Renesis engine - is pressue useless because physics tells us so or perhaps usefull because practical tests (IE dynos) have shown us that it is ?

zoom44

manson - in - his - house