Ram Air Effect

[Joy Pathak]

So I found out at wayne state event that Ram air is allowed now for 2007 cars.

I was wondering as to people's opinions on how the pressure change with Ram air Effect would affect the volumetric efficiency of the intake?

[Joy Pathak]

So I found out at wayne state event that Ram air is allowed now for 2007 cars.

I was wondering as to people's opinions on how the pressure change with Ram air Effect would affect the volumetric efficiency of the intake?

[Garlic]

About 1% at 100 MPH.

[Joy Pathak]

have you done any analysis/calculations for this?
I assumed it would be around that..
If you have...it wouldnt be possible to have a look at your calculations would it? Or what method would I use to get an exact number?

If you cant divulge in that information...it's quite alright...any form of help is highly appreciated sir.

[Jersey Tom]

Ram air has always been allowed, no? Personally, and I havent run the numbers, I dont feel the effect would be appreciable. Especially running restricted.

[BeaverGuy]

The calculation is quite trivial if you have had exposure to gas dynamics and understand the Isentropic Flow tables. Take the speed of the car and divide by the speed of sound. This gives you the Mach number of the air relative to the car and presumably the air intake. Go to the Isentropic Flow table and find the value of P/Pt for the given Mach number. Take the inverse of P/Pt this gives the ratio of the stagnation pressure to the atmospheric pressure. For choked flow the maximum flow rate is directly proportional to the stagnation pressure Pt. And it I calculate the change in pressure as 1.2% at 100 MPH which makes ram air meaningless for these cars.

[absolutepressure]

I haven't taken fluids yet, so I have a question. Wouldn't the cross sectional area of the opening of your scoop determine the amount of ram air? To give an extreme example, lets say that the opening to your scoop was 3ft in diameter and about 3-4ft long. Wouldn't that cram a lot of air into the engine even at 40mph?

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BeaverGuy:
The calculation is quite trivial </div></BLOCKQUOTE>

Yep! http://fsae.com/groupee_common/emoticons/icon_smile.gif

[drivetrainUW-Platt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by absolutepressure:
I haven't taken fluids yet, so I have a question. Wouldn't the cross sectional area of the opening of your scoop determine the amount of ram air? To give an extreme example, lets say that the opening to your scoop was 3ft in diameter and about 3-4ft long. Wouldn't that cram a lot of air into the engine even at 40mph? </div></BLOCKQUOTE>

You can go both ways with this....
Would the extra drag from having that big funnel slow the car down because of its huge frontal area. I dont think we go fast enough to even make a 3 foot deal do much, if you want ram air hook a tube to the drives mouth and have him blow in the intake

[absolutepressure]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by drivetrainUW-Platt:
if you want ram air hook a tube to the drives mouth and have him blow in the intake </div></BLOCKQUOTE>

And let the engine painfully collapse your lungs and continue to suck your internal organs through a 20mm restrictor.

[Jersey Tom]

Damn that would be INTENSE.

[Joy Pathak]

hahhaha Ouch

[Wesley]

You could get a local politician to come by and blow into the tube for you.

Might want an intercooler in that case though. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[VFR750R]

I'm shooting from the hip here but I think Cross section would allow you to stay closer to 'therorhetical max' one a flow rate is added to the equation. Once you have a flow rate then the pressure drops, so a bigger 'funnel' would keep up better but to get the max stagnation pressure the flow would either be zero or the funnel infinitely large. Of course diminishing returns determines the size of the actual ram air entrance.

Our cowl pressure goes up with speed but down with flow rate. For instance at bigger tracks we have more cowl pressure and when you let off at speed the pressure goes up further still.

[Joy Pathak]

The Cornell car has ram air intake?

And..

So you would recommend on Ram air intake even though their is only 1.2ish % pressure difference change on the VE....?

[Jersey Tom]

VFR if I remember right works at Ross Childress racing and is probably referring to one of their cars..

[AK UT]

I think you are right Tom, since turbo cars don't need a ram air intake. Look at Champ Cars vs. Indy cars, the champ cars have no intake above the roll hoop like Indy Cars do.

[Garlic]

If you wanna know where the guy works, (and spell it right), takes one click on the profile.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I think you are right Tom, since turbo cars don't need a ram air intake. </div></BLOCKQUOTE>

And what is your explanation for why turbo cars don't benefit from a higher inlet pressure?

[Kirk Feldkamp]

Keep in mind those are both spec chassis series.

If you supply a turbo with more absolute pressure on the compressor inlet, then you'll get more absolute pressure at the outlet. Plain and simple.

-Kirk

[AK UT]

They aren't really spec series, champ car is becoming one next year, but many manufacturers have built chassis for those series, and some teams have also built their own chassis, penske for example. I guess I'm just a little confused why the F1 cars from the turbo era also didn't have ram air inlets. I can't think of any turbo formula cars with ram air.

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by AK UT:
They aren't really spec series... </div></BLOCKQUOTE>

Spec chassis no.....but spec motor package yes. In Champ Car each team isn't trying to make as much power as possible like in years past. Now Cosworth builds the motors, and they all make 750hp....the teams really don't have anything to do with it.

[AK UT]

but still, even when it was honda, mercedes, ford, toyota, all battling for more power, the cars did not have ram air. which once again leads to my question of why dont turbo formula cars have ram air? I'm not saying turbotwig is wrong, what he says makes total sense, but why don't you actually see it in any racing application?

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by AK UT:
but still, even when it was honda, mercedes, ford, toyota, all battling for more power, the cars did not have ram air. </div></BLOCKQUOTE>

Wrong.

Just because it's not staring you in the face doesn't mean it's not there. Turbo cars generally have air inlets close to the turbo... and that spot varies. Look at the Audi R8/R10.

The inlet mey be in the sidepod, etc but I've seen plenty of CART cars with turbo ducts using the ram air effect.

Just because you can't see it on TV doesn't mean it doesn't exist.

[Kenny T Cornett]

http://www.mulsannescorner.com/Bentley-BC17.jpg

Perhaps to lower CG... put the intake as close to the compressor as possible to prevent losses. However, there are most of the time scoops to aide in the ramming of air into the filters

(similar engine)
http://www.mulsannescorner.com/Audi-MF7.jpg
http://www.mulsannescorner.com/Audi-PM1.jpg


An example from an actual turbo F1 car...
http://www.racingsportscars.com/f1/1979/Watkins_Glen-1979-10-07-016.jpg
http://ulysse.mines.inpl-nancy.fr/~duval85/renault/1977turbo.jpg (http://ulysse.mines.inpl-nancy.fr/%7Eduval85/renault/1977turbo.jpg)

[AK UT]

thanks kenny, as soon as garlic stated that just because you cant see it on tv doesnt mean its not there i tried to find some good pictures. those are great. i still swear there was an article in racer magazine or on speedtv.com that was describing the design process for the new dp01 champcar that said it didn't need the ram air because of the turbo engine. but of course we know that those are written by journalists and not engineers.

[VFR750R]

Turbo drag cars have inlets sticking out the front bumper 99% of the time.

You'd be amazed where ram air can be found when you know the rules of the series. For instance Cup cars have standard cowls, but they build significant ram air from the high pressure built in front of the winshield. In the truck series there's even more because the winshield is more vertical.

[Kirk Feldkamp]

After seeing how the "real world" operates from this side of the fence, I can pretty much say categorically say that what makes sense in theory rarely makes it's way into reality. I've been saying for a long time that Cornell (or whoever is being idolized at any particular time... Ferrari, Renault, Audi, etc.) could tell everyone how they build their cars... but they people they tell still has to go figure out how to do it for themselves. There is a hell of a lot more to it than understanding the theory behind an idea.

I've also seen a plethora of "great ideas" that just don't make any sense. Impracticality tends to rear its ugly head when a design is transformed into reality. This impracticality could come from a number of different sources. Granted a ram air intake isn't brain surgery, but there is a point I'm trying to make here. Just because it seems like a simple no-brainer to do something a certain way, that doesn't mean that it's actually better once you test try to build it and test it. The most common thing I've seen here in the OE world is that something that would make sense in a racing application makes absolutely no sense in the OE world (usually due to cost and production considerations). Time and money rule the OE world, and if some feature isn't necessary to meet a product specification, then it sure as hell isn't going to see production. This VERY MUCH applies to race teams as well (as you're all finding out) in that there is never enough time or money to test out the fancy pieces that get imagined up. The fact that a widget doesn't make it onto a race car doesn't mean that it doesn't work for that race car... or that it doesn't work in some other application. Shoot, look at it from the other side... just because someone else is doing "it", definitely doesn't mean that you should do "it" as well. There are plenty of FSAE cars that prove that every year. This is why I always try to tell people to look for hints on other race cars, but impartially analyze and test "it" in your application if you see fit. Only then are you going to see if it's going to work for you. This should help a program seek out the "best bang for the buck" items that benefit a particular application. If "it" didn't work, then maybe you shouldn't try "it" again without seriously evaluating the merit of the part or process.

Think about this in relation to Champ Car in its current and future incantations. Frankly, if there is a spec chassis, spec engine series, why spend the extra time, effort, and money developing and qualifying a system that doesn't technically need to be there?! The world of "Spec Series" enginneering is ALL about COST. If you didn't realize that, take a second to let that sink in. In a non-spec (competitive), high speed series like the LeMans series, if a builder isn't using ram air, they're just dumb. If F1 were still running turbo cars today, you'ld be damn certain they'd be running ram air intakes. Keep in mind there is always a discovery period associated with any "cutting edge" field. Just because someone used to do or not do something doesn't mean they actually knew what they were doing yet. This is what testing and validation is all about!

How does this apply to FSAE cars? The analysis that some people on this forum have shared says "probably not". If you've been a systems designer for long enough and have struggled with complicated layouts (like engine systems, and especially turbo systems), then you can appreciate that there are other many compromising components that take precident over ram air in most applications. In a FSAE application, I would take weight savings and polar moment considerations over "bitchin' looks" and ram air any day of the week. Space is at a premium on these little cars, and your layout shouldn't be compromised because of some widget that you haven't tested or validated. Plain and simple. These sorts of trade offs are what a design group has to develop and STICK TO if they're going to have a coordinated, intelligent design for a system. This is the primary failure of OE design engineering that I have seen to date. This is also why a well made car tends to look "simple". This is what I believe to be behind the "keep it simple stupid" phrase that we throw around on here so much.

That is all. http://fsae.com/groupee_common/emoticons/icon_smile.gif

-Kirk

[VFR750R]

Kirk, you could have just gone with 'no'.

And I'm in complete agreement. Ram air is not lap time effective at FSAE speeds, but conscienceness of your air inlet conditions are a good thing. It is still important to have your inlet breathing cool air, and by breathing air in a forward facing direction vs a position under a body panel with a radiator for instance is better. Just don't expect anything extra.

[Mike Flitcraft]

I remember a test actually done on a C5 vette a few years back. It took around 140mph if memory serves me right for there to be 0 inches of vaccume after the air filter.

I wouldn't look at it as a possible benefit for pressurized air, but rather an easier way to get some of the coldest air you can get by the rules.

O2 content increases lineraly by temperature decrease...and that has a nice benefit.

[Kirk Feldkamp]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFR750R:
Kirk, you could have just gone with 'no'. </div></BLOCKQUOTE>
Yeah, but what's the fun in that? Kids these days with their "why?"... I tell you what... back in my day...

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Michael Flitcraft:
I wouldn't look at it as a possible benefit for pressurized air, but rather an easier way to get some of the coldest air you can get by the rules.
</div></BLOCKQUOTE>
It's more the STATE you care about... and really it's density that you should really care about.

-Kirk

[Nihal]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Yeah, but what's the fun in that? Kids these days with their "why?"... I tell you what... back in my day... </div></BLOCKQUOTE>

So.. you've finally admitted your the creepy (and pompous) old guy that hangs out with the young kids.

[Joy Pathak]

There wouldnt be any horsepower benefits obviously from ram air at this speed.

I still gotta figure out how to get density into the equations. http://fsae.com/groupee_common/emoticons/icon_frown.gif

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">just because someone else is doing "it", definitely doesn't mean that you should do "it" as well. </div></BLOCKQUOTE>

So hard to convince people of this..

[Joy Pathak]

was that directed towards ?

If so...I never mentioned we are "doing it".. I just stated i am doing some calculations and analysis on its benefits...and how it might possibly help our car...
Nothing wrong with researching now is there?

If not... Carry on sir. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Mike Flitcraft]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by turbotwig:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFR750R:
Kirk, you could have just gone with 'no'. </div></BLOCKQUOTE>
Yeah, but what's the fun in that? Kids these days with their "why?"... I tell you what... back in my day...

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Michael Flitcraft:
I wouldn't look at it as a possible benefit for pressurized air, but rather an easier way to get some of the coldest air you can get by the rules.
</div></BLOCKQUOTE>
It's more the STATE you care about... and really it's density that you should really care about.

-Kirk </div></BLOCKQUOTE>

I know, I stated "O2 content increases lineraly by temperature decrease...and that has a nice benefit."

Same exact reason why anybody with a brain using forced induction has an aftercooler of some sort.

[Mike Flitcraft]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pathak:
There wouldnt be any horsepower benefits obviously from ram air at this speed but the air will be much more denser and if the atmospheric pressure can be got up around the intake the benefits would be unreal. Thats what i am concluding at the moment from all the math and isentropic analysis i have been doing.

I still gotta figure out how to get density into the equations. http://fsae.com/groupee_common/emoticons/icon_frown.gif </div></BLOCKQUOTE>

http://www.comune.siena.it/meteo/help%20inglese.htm

Air Density (in Kg/m3) = 1.2929 X 273.13 X ( AP - ( SVP x RH ))

( T + 273.13) 760

Where:

T = Temperature in Celsius

AP = Absolute Pressure (mm of Hg)

SVP = Saturation Vapor Pressure of air over water at temp T (see Table 1 below)

RH = Relative Humidity (decimal)



http://www.uigi.com/air.html
Air's O2 content by volume=20.95%, or 23.20% by weight (dry).

It's going to be very hard to find a chart since the O2 content is dependant upon humidity as well as temperature. I doubt many people have lab created the scenarios...

[Bill Kunst]

I have been watching this thread for awhile, and haven't seen someone ask the complex question of...
"Throughout the speed range, what is the average increased Hp/Tq that will be seen from a ram air unit??? Take that into effect on the style of courses we see, and the average speeds, and how will that increased avearge hp effect lap times?"

I think that if one were to look at this (dismissing thoughts on 200mph cars), and this is mostly a waste of research, although it may look "COOL".

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bill Kunst:
I have been watching this thread for awhile, and haven't seen someone ask the complex question of...
"Throughout the speed range, what is the average increased Hp/Tq that will be seen from a ram air unit??? Take that into effect on the style of courses we see, and the average speeds, and how will that increased avearge hp effect lap times?"
</div></BLOCKQUOTE>

I figured that wetn without saying. If it's only 1% at 100 MPH, then seems pretty obvious the benefity is not there.

[VFR750R]

So if your motor is making 80hp then that's .8hp at 100mph, .2Hp @ 50, .05hp @ 25mph and a significant .0125hp @ 12.5mph.

As far as lap times, my calculations say a properly placed radiator fan can produce more thrust and a faster lap time on tracks with up to 22.397mph avg speed.

[Mike Flitcraft]

I hope you don't mean placing the intake for your motor behind your radiator....

[Matador Motorsports]

Just to add to the complexity also consider engine RPM... Here's something to consider. Say at the 12.5 mph you are getting the very significant HP boost that the engine and turbo guy provide, I ask why hasn't anyone even considered the operating engine RPM? if you're choking the restrictor at any velocity, even at 100mph (which we'll never see), if your revving the engine past the choke point then the ram effect will be 0%. So I would say the ram air effect is productive only if you turbo/super charge it!

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Matador Motorsports:
if you're choking the restrictor at any velocity, even at 100mph (which we'll never see), if your revving the engine past the choke point then the ram effect will be 0%. So I would say the ram air effect is productive only if you turbo/super charge it! </div></BLOCKQUOTE>

This is incorrect, and I'll let you figure out why. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Matador Motorsports]

Well Garlic,

Point of clarification here...

If you're saying you can force more air through the restrictor past the choke point, your mistaking and I'll let you figure that one out. With a turbo/super even at this point won't help either. If you want a "ram" effect I was saying you should just use a turbo/super charger.

[buddy]

As someone who has worked at Flow-Dyne Engineering, I'm agreeing with Garlic here, and we'll both let you figure out why.

[VFR750R]

Garlic is right, the choke point is variable depending on inlet and outlet conditions.

[Julio_93]

Garlic, Buddy, I have to side with Matador Motorsports on this topic. Once the restrictor is choked (reaches a critical pressure of .528) the mass flow rate cannot be exceeded. Please refer to Internal Combustion Engine Fundamental by John B. Heywood, appendix C. If you do not have this text then you can refer to this following website which explains it very well.

http://www.engapplets.vt.edu/fluids/CDnozzle/cdinfo.html

[Matador Motorsports]

Alright, I'll really let you guys go settle this one...

You can take the easy way and just ask your fluids professor if you want a quick confirmation.

If you look at the mass flow equation for compressible fluids, you'll see a pressure ratio of (pressure at the throat) / (pressure at the outlet). Now as you non-believers should know the pressure at the outlet for an ideal case should be the same as the inlet pressure. If you increase the inlet pressure, the outlet pressure will be increased by the same amount. Now you can keep increasing the inlet/outlet pressure up or down and you'll find that there's a critical pressure where no matter what you do, you cannot exceed the mass flow rate once you have reached choked flow. The equations don't lie, and they can't distinguish between pulling/pushing air through the restrictor because it only depends on that pressure ratio.

Take a look at the internal combustion text by Heywood, which is a must for FSAE teams. Restricted flow is reviewed in Appendix C.

It was fun guys!

[BeaverGuy]

Garlic, Buddy, and VFR750 are correct. Where you are wrong Julio and Ricardo is that the choke point changes with stagnation pressure and temperature. The ratio you give of 0.528:1 is of the static pressure at the throat to the stagnation pressure, not the outlet pressure. With a "ram air" intake, converting the kinetic energy of moving air into pressure energy, stagnation pressure increases. This increases the amount of air that is possible to cram through the restrictor.

[VFR750R]

Equally as important, if you increase your inlet pressure you increase the density as .528 of a higher pressure is a higher pressure itself and thus a higher density to the air going through the restrictor.
Additionally, the with the coolest air possible you will have a density increase even though the speed of sound is slower in colder air.

Higher density air leading to higher mass flow rate is why you never see a restrictor after a turbocharger. The turbo can actually lead to much much higher flow rates through the restrictor.

This can also be applied to exhaust valve blowdown. The 'choke point' in mass flow/square area is constantly changing during the process.

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BeaverGuy:
Garlic, Buddy, and VFR750 are correct. Where you are wrong Julio and Ricardo is that the choke point changes with stagnation pressure and temperature. The ratio you give of 0.528:1 is of the static pressure at the throat to the stagnation pressure, not the outlet pressure. With a "ram air" intake, converting the kinetic energy of moving air into pressure energy, stagnation pressure increases. This increases the amount of air that is possible to cram through the restrictor. </div></BLOCKQUOTE>

Perfectly stated, and I hope you guys who say otherwise haven't taken a fluids class yet!

[Matador Motorsports]

Hey Guys,

Sorry wasn't around to respond earlier since I was at the SEMA show with Julio. Good times right Julio?

Yeah... by increasing the stagnation point it is possible to flow more mass through the restrictor because you might not be operating at the choked flow criteria. If you increase your inlet pressure and are still in choked flow conditions you can't flow more than what occurs at choked conditions, which now depend on your new stagnation pressure. Now, the section that I wasn't clear on was in comparing the two scenarios. I do agree that you can have a higher mass flow with an increase in stagnation pressure, but in a 100 mph scenario, the increase in stagnation pressure is only about 0.12 Pa, which in comparison to ambient pressure 101kpa is nothing. That's why I suggested that if you want a "ram"� effect use a turbo/super charger instead.

Now back to FSAE....
The rules strictly ban the use of a turbo/super charger upstream of the restrictor for this purpose. So you're stuck with using only other ways of increasing the minimal ram effect than what is available at out top speeds. Kinda like what VFR750R suggested with the radiator fan.

[Diablo_niterider]

its no use for them they have to run a spec valve on the plenum , every time it reaches a boost pressure higher then what rules allow it blows off , and they average at quite high speeds for its useless for them