Restrictor design

[zoomzoom]

hi all,

i know that this is probably a pretty sensitve topic for most teams, but i was wondering if anyone would care to comment on their restrictor design.

in the past we've run pretty much straight converging/diverging angles(chosen from info in Fluids texts) with around 5mm in the centre at 19.90. Another team member recently found a supposedly 'close to optimal' nozzle profile from some fluids journal which has a number of radii in its design. He also says there is a better version available but that we have to pay like $100 bucks for it.

Just wondering what everyone else does. Do you use straight angles or a special profile?

If you use a special profile do you think its worth the effort? Any rough numbers to share?

[MoTeC]

Do you guys have a flow bench to test the difference nozzel shape makes? Just trying to get a feel of where most development is done, I think different teams concentrate on different areas.

Donna

[Richard Lewis]

Not going to divulge too many secrets here. http://fsae.com/groupee_common/emoticons/icon_wink.gif But take a look at what F3 used to do, because they were running a very similar restrcitor setup.

Equal angles on convergence and divergence is not optimal. The ideal inlet shape is a radius... as for diffuser angle, there has been ~50 years of research done on diffuser angles, lengths, etc, so there is info available if you know where to look.

-------------------------
UVIC Formula SAE Team
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http://uvic.fsae.ca

[Frank]

K&N airfilter RC 2440
34mm throttle
30 degree (inc angle) inlet
60 mm radius
19.94 mm final diameter
0.3um RA surface finish
14 degree (inc angle) outlet
34 mm final diameter

flow bench test on professional, calibrated Superflow SF 600 Flowbench (the above items only..ie through filter to base of restrictor)

10" 77.5 CFM
20" 106.5 CFM
30" 124.5 CFM
43" 134 CFM (choked)

engine standard CBR600 F3 98RON Fuel
Motec Sequential ignition
1.1 Ltr plenum volume (measured from air horns to throttle plate)
68 BHP @ 10250 rpm @ shaft
testing performed on regularly calibrated, professional engine dynamometer, inertia correction, and SAE J607 correction (Stafford tune, Brisbane)

thoughts:

1 exit angle too large... (use 10 degree inc. angle exit next time)

2 exit diameter too small.. (use 46mm exit diameter next time)

3 plenum volume adequate.. (dont exceed 2 Ltr... we found 3 ltrs too much)

Frank

ps..

this was nozzle no 3, am happy with the profile upstream and in the vicinity of the orifice.. restrictor no 4 being SLS'd at the moment.. update soon

"These cars feel great.. SIDEWAYS"
http://www.uq.edu.au/fsae/2002fsae.jpg

[This message was edited by Frank on March 13, 2003 at 07:57 AM.]

[Dominic Venieri]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by MoTeC:
Do you guys have a flow bench to test the difference nozzel shape makes? Just trying to get a feel of where most development is done, I think different teams concentrate on different areas.

Donna<HR></BLOCKQUOTE>

We have our own SuperFlow 110 flowbench. A student just finished up a semester long project for credit on our restrictor design. He tested numerous restrictor prototypes, the designs for which were based largely on published data. The final design was (will be) tested on our chassis dyno.

www.formularpi.com (http://www.formularpi.com)

[Marc Jaxa-Rozen]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Equal angles on convergence and divergence is not optimal. The ideal inlet shape is a radius... as for diffuser angle, there has been ~50 years of research done on diffuser angles, lengths, etc, so there is info available if you know where to look.<HR></BLOCKQUOTE>

Ditto...many teams use simple convergent-divergent shapes, which are easy to manufacture but don't offer the same performance.

Heck, just look at wind tunnel shapes.

[V2 - Italy]

I wrote to the Formula Student committee, to clarify the 3.5.4.3 rule (intake system restrictor).

Dr Andrew Deakin replied:

You are allowed only one 20mm restrictor through which all the engine's
air must pass. This means that you must design a new intake system for
your engine which can use either fuel injection or carburettors (usually
one carburettor) to achieve this.

With regard to engine sizes, you have freedom to use any 600cc engine
and it is up to you to choose the one which when modified will give you
the best power and torque characteristics. Therefore, I expect my
American colleagues will not go for your suggested rules change, but I
will ask them.

Regards and best of luck,
Dr Andrew Deakin
Formula Student Technical Rules

-----Original Message-----
To: D_Atton@imeche.org.uk>
Subject: Formula Student Rules

Dear FSAE,

we need to clarify the 3.5.4.3 rule (intake system restrictor):
...a single circular restrictor must be placed in the intake system
between the throttle and the engine ...

We are using a twin cylinders engine with two carburetors.

Is it correct to place the restriction after each carburetor, before the intake valve?

---------

Please, if someone used carburetors in the past, could tell us how designed the restrictor, and where did you place it?

Firenze Race Team V2

http://www.firenzerace.too.it

DUCATI POWER at the UniversitÃ* di Firenze

[Dominic Venieri]

the simplest way would be to make a plate with the proper 20mm opening that bolts between your carb and your manifold. you could also use a nozzle type restrictor much in the same way that the fuel injected cars do. i've seen many first year, carb'd teams use the plate approach because it is easy and cheap to make, since you have so much else to worry about in getting a good car built and sorted.

www.formularpi.com (http://www.formularpi.com)

[Marc Jaxa-Rozen]

Wouldn't the pressure phenomena resulting from a venturi restrictor and a resonance-tuned manifold upset the carb? I remember reading someone had trouble with this.

If so, a simple plate restrictor (NASCAR-type?) might work best...

[Ben Beacock]

why not remove the throttle plates from the carbs, then make a restricted intake with a throttle plate ahead of the restrictor? That would satisfy the rules but I don't know how well the carbs would work(bad idle, no accelerator pump) and it probably wouldn't work with slide carbs (i've never worked with those)

Ben Beacock
Chassis Design and Technical Coordinator
Gryphon Racing - University of Guelph

[Richard Lewis]

We ran a carb last year and had a terrible time with it. (due to lack of setup time) Make sure you use a really small (ie: ~30mm... maybe smaller) carb, otherwise you'll have all sorts of problems. (we ran a 38mm last year... only way to get it to work well was restrict the carb opening, so that air velocities stayed high. Even then, it would stall under 5000rpm)

I'd even look at really small (22-24mm) carbs if you can find one to try out.

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UVIC Formula SAE Team
http://members.shaw.ca/drax77/Formula%20UVic%20Sig.jpg
http://uvic.fsae.ca