Engine Decision

[Engine Dude]

Hey Guys
We are a team trying to solve engine turbo problems. Can any team tell me at what engine speed a NA 600cc four cylinder will choke?

Also for a single of the same or close size??

Regards

ZAC

[Engine Dude]

Hey Guys
We are a team trying to solve engine turbo problems. Can any team tell me at what engine speed a NA 600cc four cylinder will choke?

Also for a single of the same or close size??

Regards

ZAC

[Jeff The Pyro]

by the math... with a well designed venturi style restrictor, somewhere around 12,000 rpm. it may spin faster but torque will rapidly fall...

we havent been able to (or really wanted to) make power past 10,500 on our old school fzr600 (which wasnt designed to see high revs in the first place)

mathematically, a single cylinder should be identical to a four cylinder, but its pretty safe to assume the single cylinder will have lower volumetric efficiency.

[Kirk Feldkamp]

It's going to choke long before 12,000. Depending on how much boost you plan on running (coupled with an RPM), you can choke the restrictor much lower in the rev range. Where are you from Engine Dude?

-Kirk

[Bowtie Man]

Engine Dude,
Our Gixxer's torque peaks at 11000rpm NA, i'm not sure if you were at competition this year but Cornell did a pretty good breakdown on 4 cylinder engines and getting a hold of their posterboard from the design presentation might be valuable as far as decision making goes.

Luc
University of Manitoba
Engine/Drivetrain

[Bowtie Man]

Engine Dude,
I just found a pic of their poserboard, email me and i'll send it to you.
umgroen0@cc.umanitoba.ca

Luc

[Kamil S]

Hey Bowtie Man,
Is it OK if I can have a copy of that file?
Let me know, thanks!

[kwancho]

ditto here. kwancho@stanford.edu. thanks!

[Psychosis]

me three please! lau01220@strath.ac.uk

[Bowtie Man]

send me an email if you want the pics i've got

[Engine Dude]

Hey I am from Australia.

We have planned everything for the F4i turbo, however someone in our team thought of going a single.

Thanks guys

Sam.

[threehondas]

Could I get a pic of that design poster?

Would it be rude/unprofessional to post it somewhere? I suppose we could ask Cornell?

According to my airflow sheet, I figured I choke at 9500RPM@180kPa MAP, intake air temp at 51deg c, with a 470cc single, and on the dyno torque falls considerably after 9500rpm.

With the same single running NA I was not able to choke the restrictor, since I got more torque than stock (or close to it) across the entire rev range.

The same sheet puts a 600cc motor with air temps at 25 deg c, choke should be around, 12250 RPM, which is close to our old F4 who's torque fell at 11,500 and was really falling by 12250 RPM.

[threehondas]

Kirk,

Do you think you choke around 6900RPM? Your torque fall much after that? Where's your peak?

[Engine Dude]

Bruce,

When you are predicting choke at a particular rpm, are u calculating the airflow past the restrictor and then relating that to volumetric effeciency?

I may be way off here, but I am having trouble finding a suitable way of predicting the rpm for choke. I just got some engine software and will have a look at it soon, but looks like time is running out (FSAE-A is this December). I just want to get the thing on the dyno asap.

What boost level are you running at the moment on your single. I have been following your progress.....congrats!

Regards,

Sam

[Engine Dude]

Sorry I meant what boost level did you run at the comp.

Sam.

[threehondas]

Sam,

We generate 182Kpa (~11psi) of boost from 5500 to 9500RPM.

I use a spread sheet -

Compressible flow equations for max Mdot in isentropic choked flow in the throat of a diffuser. You can get as fancy as you'd like with assumptions and more information. I use intake air temp, manifold air temp, restrictor area, manifold pressure, A*, VE and the spreadsheet figures the rest out.

You might have the same textbook as me??? F.M. White ('03 model), eq 9.46b, 9.50, 9.51, 9.52. pp. 462&615.

I guess a proper fluent analysis is better but I've never seen someone verify it so what's the point? My friend Sean put our old diffuser on a flow bench (by flow bench I mean ford v6 intake) and watched it go choked (pressure taps along its lenth) and checked the CFM. And it was close enough to the spreadsheet. Engine simulations... seems like everyone does them but are the trends the same as on the dyno? If they are they could be useful. I'll probably be doing both next year for a fourth year project; virtual four stroke (VFS) and fluent analysis for intake and exhaust. We'll see if they're worth my time. I'd love to hear from other teams about this??? Maybe the judges love that stuff (fluent and VFS)? I guess spreadsheets and dyno data to verify results hardly pass as "engineering tools" these days - because judges seemed less than impressed with the our powertrain.

Thanks for the props about the motor Sam, but too much oil in the intercooler killed us in endurance (as I predicted in another post). So it was all for nothing really. Shoulda, coulda, woulda, same old 'we need more testing time' bs. Some year Queens will finally learn their lesson.

[Kirk Feldkamp]

No, we hit choke a lot higher up. It's somewhere in the region of 9500rpm. We hit peak torque at 6250, and peak power at 9500. After peak power, torque drops off like a rock. We really have to start throwing more fuel at it in the 9000-10500 region to keep it happy. I'm going to back calculate airflow today with our BSFC and lambda numbers. Bruce, I think we're both surging the bejesus out of the turbo, not overspeeding it like we talked about. With our lowered compression and high boost we're really overworking the turbo. We're working on bumping the compression back up and an intercooler. BTW, does anyone on the west coast know who to talk to about getting E85? We're in need of getting our manifold temps down... or getting a whole bunch more charge cooling.

Oh yeah, with the wastegate and no boost controller, the boost sits right at 8psi... that will help your calculations a bit.

-Kirk

[BeaverGuy]

When we ran E85 we mixed it ourselves. We bought the ethanol and race gas from Wilcox and Flegel in Washington but I'm sure there are Sunnoco distributors in Cailifornia. I don't know if anyone sells E85.

[Kirk Feldkamp]

I'm going to sound like a complete goon here, but is E85 just 85% pure ethanol and 15% GT100?

-Kirk

[MikeWaggoner at UW]

It is 85% ethanol, the rest is usually just defined ambiguously as 'gasoline'.

[VFR750R]

I'm pretty sure most E85 mixes are with 93 octane pump fuel.

[Mechanicaldan]

E-85 is available at select gas stations all around the Midwest. That doesn't really help you on the west coast though.

[jonny]

Hi,

How do you calculate the mass flow rate of the restrictor when it chokes and the rpm of the engine that causes this.
I am using a simple calculation that gives me 0.12441kg/s. Here is my equations:
1) Find area of restrictor
2) Find volume flow rate using area x velocity ( use 330m/s here ie the speed of sound, since air cannot travel at this speed)
3) Multiply 2 with th density of air.

Is this method correct??

[Pete M]

No, it isn't because the density of the air changes with mach number. You need to grab a fluids textbook and read the chapter on compressible flow.

[Wesley]

Don't forget that the restrictor doesn't see steady-state pressure differentials.

You won't hardly ever reach the theoretical choked flow rate because of standing pressure waves that develop in the manifold and at the throat of the restrictor in an actual operating environment.

I don't know how many teams I've seen completely neglect the fact that engines don't operate at steady state pressures.